1 MULTICHANNEL DIGITAL AUDIO DECODING SYSTEM FOR CONSUMER PRODUCTS
Licensee Information Manual Version 2.0 April, 1997
Dolby Digital Licensee Information Manual version 2.0 April, 1997
Table of contents Change highlights in this revision................................................................................................5 1. Product design overview .........................................................................................................7 2. Introduction to Dolby Digital ..................................................................................................7 3. Licensing ................................................................................................................................8 4. Product functions, product logos .............................................................................................9 4.1. Source products vs. decoder products .......................................................................9 4.2. Source products with internal decoders ...................................................................10 4.3. Bitstream Source products ......................................................................................11 4.4. Trademark and logo usage ......................................................................................12 4.4.1 Usage guidelines for Dolby logo and trademarks on products...................13 4.4.2 Trademark acknowledgment; license and copyright notice .......................13 4.4.3 Laser disc players with Dolby Digital RF outputs.....................................14 5. Product specifications and requirements ................................................................................15 6. Product Groups and Standards...............................................................................................16 6.1. Definition of product Groups ..................................................................................16 6.1.1 Definition and examples of Group A products..........................................16 6.1.2 Definition and examples of Group B products ..........................................17 6.1.3 Definition and examples of Group C products ..........................................17 6.2. Definition of product Standards ..............................................................................17 6.2.1 Standards for all product Groups ..............................................................18 6.2.2 Standards for Group A products ...............................................................21 6.2.3 Standards for Group B products ...............................................................22 6.2.4 Standards for Group C products ...............................................................22 7. General product design considerations...................................................................................23 7.1. Product input and output connections, copy control ................................................23 7.1.1 Line input and output design ....................................................................23 7.1.2 Balanced audio connections......................................................................23 7.1.3 Multichannel connections .........................................................................23 7.1.4 Color coding output connections ..............................................................25 7.1.5 Headphone output connections .................................................................26 7.1.6 S/PDIF Dolby Digital and PCM digital interface......................................26 7.1.7 RF transmissions for wireless speakers.....................................................27 7.1.8 Dolby Digital RF carrier inputs and outputs .............................................27 7.1.9 USB, IEEE 1394 outputs..........................................................................27 7.2. Controlling output levels.........................................................................................28 7.2.1 Master volume control..............................................................................28 7.2.2 Gain trims, balance controls .....................................................................28
2 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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7.3. Audio features of Dolby Digital..............................................................................29 7.3.1 Dialog normalization................................................................................30 7.3.2 Dynamic range control .............................................................................31 7.3.3 Downmixing audio...................................................................................31 7.3.4 Operational modes....................................................................................32 7.3.5 Using operational modes in products ........................................................36 8. Design considerations—stereo products ................................................................................38 8.1. Mode switches and indicators—stereo products ......................................................39 8.2. Specific considerations for 2-channel televisions ....................................................39 9. Design considerations—multichannel products .....................................................................40 9.1. General product structures ......................................................................................40 9.2. Mode switches and indicators—multichannel products ...........................................42 9.3. Listening mode selector ..........................................................................................43 9.3.1 Listening modes .......................................................................................44 9.4. Products with additional signal processing ..............................................................46 9.5. Source selector switching........................................................................................48 9.6. Tape and headphone outputs ...................................................................................49 9.6.1 Headphone outputs ...................................................................................49 9.6.2 Tape outputs.............................................................................................49 9.7. Program format display ..........................................................................................50 9.7.1 LFE channel and display ..........................................................................51 9.8. Output Configurations ............................................................................................52 9.8.1 Bass signal levels .....................................................................................56 9.8.2 LFE and subwoofer level controls ............................................................57 9.8.3 Bass from multiple speakers .....................................................................58 9.8.4 Bass limiting ............................................................................................59 9.8.5 Crossover filters .......................................................................................59 9.9. Speaker options and power amplification................................................................60 9.9.1 Speaker selection options .........................................................................60 9.9.2 System power amplification .....................................................................61 9.10. Decoder gain correction ........................................................................................62 9.10.1 Maintaining balance across channels ......................................................62 9.10.2 Gain structure for decoders with multichannel inputs .............................63 9.10.3 Maintaining balance across decoder modes.............................................65 10. System calibration ...............................................................................................................67 10.1. Surround time delay..............................................................................................67 10.2. Center time delay..................................................................................................68 10.3. Channel balance—test noise..................................................................................69 10.4. System self-calibrator ...........................................................................................69 11. Dolby Digital adaptors ........................................................................................................70 11.1. Outboard adaptor ..................................................................................................70 11.2. Plug-in module .....................................................................................................71 11.3. 5.1-channel DVD player .......................................................................................72
3 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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12. Design considerations—Dolby Virtual products ..................................................................74 12.1. Virtual Surround ...................................................................................................74 12.2. General Product Structures ...................................................................................77 12.3. Implementation issues...........................................................................................78 12.3.1 Time delay .............................................................................................78 12.3.2 Surround channel processing ..................................................................79 12.3.3 Frontal image width ...............................................................................79 12.3.4 LFE channel ...........................................................................................79 12.4. Trademark and logo and usage..............................................................................79 13. Design considerations—personal computer products ...........................................................80 13.1. General Product Structures ...................................................................................80 13.2. Product design issues ............................................................................................82 13.2.1 Decoder implementation.........................................................................82 13.2.2 Plug-ins ..................................................................................................83 13.2.3 PCs.........................................................................................................83 13.2.4 PC speakers ............................................................................................83 13.3. Performance requirements ....................................................................................84 13.3.1 DVD players ...........................................................................................84 13.4. Trademark and logo usage ....................................................................................84 13.4.1 Plug-ins ..................................................................................................84 13.4.2 General PCs ...........................................................................................84 13.4.3 Licensed PCs..........................................................................................85
4 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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Change highlights in this revision Version 2.0 of the Dolby Digital Licensee Information Manual supersedes Version 1.0, October 1995. Areas of the manual where substantial changes have been made are identified by the presence of electronic notes in the margin next to the affected text. This feature is only available when viewing the “.pdf” file with Acrobat Reader. A complete summary of these notes follows.
Page 8
Part 3. Discussion of licensing agreements has moved to the separate document "Decoder Status".
Page 9
Part 4.1. Revised to reflect simpler product definitions due to change in logo policy from AC-3 to Dolby Digital.
Page 11
Table 4.2. Corrected data rates.
Page 13
Part 4.4.1. Simplified logo policy replaces 4.4.1-4.4.6, and 4.4.8. Part 4.4.2. All TA/LN notices revised to preferred wordings.
Page 16
Part 6.1. Added "set-top" descriptions.
Page 18
Part 6.2.1-a. Note added to explain risks in designing with unapproved ICs.
Page 21
Part 6.2.1-s. New requirement to accommodate broadcast applications. Part 6.2.1-t. New requirement to define error recovery. Part 6.2.1-u. New requirement for copy management control. Part 6.2.2-g. Added center delay specification.
Page 24
Table 7.1 Pin 12 now Reserved. Was "decoder config" control.
Page 24
Part 7.1.3. Added clarification about use of phono connectors for multichannel outputs.
Page 26
Part 7.1.6. IEC 1937 is formal name for IEC 958 when using coded audio data.
Page 26
Part 7.1.6. Copy management information added.
Page 27
Part 7.1.9. Added USB, IEEE1394 serial port section. Copy management note added.
Page 36
Part 7.3.5. Section rewritten to better reflect current practice and recommendations.
Page 39
Table 8.1. Limit the range of input signal status. Reduces similarity with multichannel products. Table 8.1. Lt/Rt downmix is a required feature in 2-dec, 2-TV, and DVD. Previously recommended default mode. Table 8.1. Dialog normalization may not be deactivated under any condition. Part 8.1. Clarified policy on use of Lt/Rt flag.
5 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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Page 42
Table 9.1. Removed 2-TV (see Table 8.1) and 2-Sur (obsolete) product definitions. Table 9.1. Added surround "downmixing" requirement. Table 9.1. Added center "downmixing" requirement.
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Part 9.4. Cautionary note added about maintaining headroom.
Page 50
Part 9.7. Use of "S" channel indicator explanation expanded.
Page 51
Fig. 9.6. Added to show examples of format display with particular programs. Part 9.7. New policy statement limiting use of program display on certain products. Table 9.6. Added to show usage of indicators.
Page 52
Part 9.8. Various revisions and clarification were made throughout.
Page 53
Part 9.8. Explanation added to describe how digital implementation might apply gain scaling. Added scale factors to Figs. 9.7, 9.8, 9.9.
Page 54
Fig. 9.8. Added note showing optional SUB output.
Page 55
Fig. 9.9. Added to show alternative Output Configuration 2.
Page 56
Part 9.8.1 Rewritten to clarify bass management concepts.
Page 58
Part 9.8.3. Added background on derivation for bass redirection signal levels. Table 9.6. Added to show relationship between bass and number of channels.
Page 59
Table 9.7. Added to show relationship between bass and number of speakers. Part 9.8.5. Relaxed filter slope for high-pass filter sections. Added recommendation for Linkwitz-Riley.
Page 63
Part 9.10.1. Clarified Dolby Digital mono surround cases. Part 9.10.2. Has all new content to clarify design concepts and requirements for multichannel inputs. Fig. 9.13 added.
Page 72
Part 11.3. Added to describe 5.1-channel DVD "adaptors".
Page 74
Part 12 added on Virtual products.
Page 80
Part 13 added on PC products.
6 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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1.
Product design overview
The design of consumer products with Dolby Digital may be divided into separate and distinct areas. As with other technologies licensed by Dolby, there is a core technology which will be implemented in either a general purpose DSP, a fully custom processor IC, or a general purpose computer microprocessor. This is known as the implementation. The host product acts as a shell around the core decoder implementation to provide the specific software interface between the end user and the input/output signals. Because audio coding is a digital process, all interfaces will be digital by nature, and the interface concepts will be standardized wherever possible. There will be various opportunities for product designers to tailor specific aspects of their products to meet the specific needs of the market, or to enhance product differentiation. Dolby supplies various materials and technical information to support the design of licensed products. This document, the Dolby Digital Licensee Information Manual, describes the product specifications and functional requirements for the use of Dolby Digital within a range of typical consumer decoder products. It includes audio specifications external to the Dolby Digital coder itself, and definitions for digital audio interface requirements. Applications information will generally be supplied by the maker of the Dolby Digital processor itself. Additional information is available for the development of Dolby Digital encoder and decoder implementations, which are covered under separate agreements. Contact Dolby Laboratories for details.
2.
Introduction to Dolby Digital
When all television and radio audio was monophonic, everyone heard mono sound. After stereo was introduced and became widespread, expectations grew for higher fidelity and greater dynamic range to complement the improved spatiality of the soundfield. Compromises were reached for acceptable mono/stereo compatibility, and while dynamic range increased with improving technology over the years, the use of dynamic range compression is still a regular ingredient of audio production. The full quality of original audio recordings is seldom transmitted to consumers fully intact. With digital delivery methods, there is a growing desire to provide the full dynamic range of the source (usually with reference to compact discs), but there is still the need to serve the majority of the audience that is listening under less favorable conditions where reduced dynamic range is essential. With surround sound in general, and now with digital 5-channel discrete delivery becoming a reality, the desire to utilize the full spatial and dynamic range capabilities of the format presents new opportunities for artistic expression, but even greater conflict and contrast with the restricted needs of the typical mono/stereo listener. Dolby Digital was designed as a versatile low bit rate audio coder intended to satisfy many diverse requirements from a single version of the program. It allows audio signals to be adapted in ways that make it compatible with a wide range of user needs, even those in direct conflict
7 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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with each other. While critical members of the audience may have impressive “home theater” multichannel reproduction systems and demand high dynamic range programs, most of the audience will be listening in mono or stereo, often under noisy or low-level conditions, and will require restricted dynamic range audio. Some listeners may have matrix-based Dolby Pro Logic multichannel reproduction equipment, thus requiring a compatible 2-channel downmix from the delivery system. All of these (and other) diverse needs were considered in the design of Dolby Digital coding technology. As an emissions coder intended expressly as the final link from the program producer to the consumer, Dolby Digital enables many new features and capabilities that were previously unattainable in consumer products. A short list of these will illustrate the point: •
Delivery of mono through 5.1-channel sound at data rates from 32 kb/s to 640 kb/s, thus offering flexibility and economical performance as well as uncompromised sound quality.
•
Separate bitstream information (BSI) containing data for positive identification of the original production format; confusion about programs being mono, stereo, matrixed or discrete surround when received is eliminated.
•
Programs will be “listening level matched” so that no matter what program source or channel is selected, there is no need to adjust the volume control to maintain a comfortable listening level. No alteration of program dynamics is involved, only playback volume.
•
When 5.1-channel programs are received, the Dolby Digital decoder can provide a matrixencoded 2-channel downmix for recording onto stereo video tape or for decoding with a Dolby Surround system. The decoder can also optimize the downmixing of mono and stereo versions, depending on the needs of the reproduction system.
•
When very dynamic movie soundtracks are played at low volume, such as late at night, the system may apply appropriate compression to ensure that the low-level program content is not lost and that high level effects are constrained. The degree may be designed to vary according to need and does not have to be an “all-or-nothing” effect.
3. Licensing Dolby Laboratories does not manufacture consumer products, and thus does not compete with its consumer product licensees. Dolby will openly license any manufacturer which is both technically capable and financially sound. Technical assistance is provided to its licensees during the development of licensed products. Typical multichannel products are licensed under a Dolby Digital agreement and a separate agreement covering Pro Logic directional enhancement. Royalties on Dolby Digital decoders are paid by consumer product manufacturers on a per product, per channel basis, and may be affected by the total number of channels manufactured in a calendar quarter.
8 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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4. Product functions, product logos The market will naturally move towards a few traditional product configurations as summarized below. If there is a need to design products that do not fit these initial definitions, please contact Dolby Laboratories.
4.1. Source products vs. decoder products It is useful to note that while all licensed products in some way decode Dolby Digital into audio, some can only decode signals from one delivery format, usually the particular disc, tape, cable, or broadcast format they support. These products are referred to as “Source” products, since they receive only specific Dolby Digital bitstream sources. Products that allow Dolby Digital decoding facilities for external bitstreams are classified as “Decoder” products. Decoder products may also incorporate Dolby Digital sources. For example, a Dolby Digital A/V receiver may also include a DVD player. If the product has an external input for Dolby Digital signals, it is by definition a Decoder product. If a product with only 2-channel Dolby Digital includes matrix-based Dolby 3 Stereo or Pro Logic processing, the applicable logo for that product shall reflect only the matrix decoding technology in use. No use of the Dolby Digital logo shall be made on the product. This is because there should be only one main system Dolby logo per product, and the logo used must best describe what effect the user will hear. As a general rule, any multichannel Dolby Digital product must include a Pro Logic decoder to ensure compatibility with existing software. While 5.1-channel adaptors are considered to be Decoder rather than Source type products, they are not required to include Pro Logic processing. Their main purpose is to add Dolby Digital to an existing Dolby Pro Logic Surround system, so it would be redundant to require Pro Logic to also be included in the adaptor. It should be noted, however, that since there will be Dolby Digital bitstream sources with Lt/Rt programs, there could be two main benefits of including Pro Logic decoding in the adaptor: •
The audio remains digital through the entire Dolby Digital delivery and Pro Logic decoding process.
•
The user can experience the maximum surround sound effect allowed by the program soundtrack without making any adjustments to the system when programs change, since the adaptor can switch between the Dolby Digital mode and the Pro Logic mode automatically.
If the main surround processor includes specific sound effects processing, however, the adaptor’s 2-channel audio output will need to be Pro Logic decoded by the main surround processor, or else these additional effects will be unavailable to the listener.
9 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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4.2. Source products with internal decoders In order to design systems capable of decoding Dolby Digital bitstreams, it is important to understand the types of signals they will receive. Sources of Dolby Digital bitstreams may include NTSC laser disc (LD); digital cable and satellite; digital television (DTV), which encompasses standard definition television (SDTV) and high definition television (HDTV); digital video cassette (DVC); and digital video disc (DVD), among others. Unlike the LD format which was retrofitted with Dolby Digital carriers as an optional signal, new delivery formats may use Dolby Digital as their sole or primary audio system. New formats will usually be fully digital for both audio and video signals, and in order to obtain the maximum efficiency in the use of the available data capacity, redundant soundtracks will be avoided wherever possible. Source products may choose to support one or more of the possible data rates and channel configurations possible with Dolby Digital, but decoders must generally be able to accept any of them. Whether the format is disc, tape, or transmission-based, in order to fit with current consumer A/V reproduction systems, Source products need to provide conventional 2-channel audio outputs. An internal 2-channel Dolby Digital decoder will therefore be the norm, even though a multichannel version of the same program may be delivered via the digital output in parallel, as shown in Fig. 4.1. The internal decoder will typically downmix any 4- and 5.1-channel programs into a compatible Lt/Rt stereo output suitable for subsequent Pro Logic decoding. L DOLBY DIGITAL BITSTREAM
2-CHANNEL DOLBY DIGITAL DECODER
AUDIO OUTPUTS R
IEC 1937 (S/PDIF) FORMATTER
DIGITAL OUTPUT
Fig. 4.1. Basic Dolby Digital Source product structure. The DVD format is unique in that it may carry PCM, Dolby Digital, and MPEG2 audio bitstreams. The player’s digital output jack may therefore offer direct PCM, Dolby Digital or MPEG2 coded audio, or PCM decoded from the Dolby Digital or MPEG2 bitstreams, as shown in Fig. 4.2. It is not expected that all players will offer all these capabilities, however.
10 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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L
2-CHANNEL DOLBY DIGITAL OR MPEG2 DECODER AUDIO DATA INPUT PCM DOLBY DIGITAL MPEG2
AUDIO OUTPUTS R DIGITAL OUTPUT
PCM
IEC 1937 (S/PDIF) FORMATTER
DATA SELECTOR
PCM DIGITAL MPEG2
Fig. 4.2. DVD audio data capabilities. In the end, the minimum signals that are provided to the A/V decoder are the same from all Dolby Digital Source products: 2-channel analog line outputs and a Dolby Digital bitstream via S/PDIF. It is important that both outputs be provided simultaneously for greatest operational flexibility in the attached A/V surround decoder.
4.3. Bitstream Source products More than one set of video or audio decoding processors may exist in a single A/V reproduction system due to the wide adoption of digital audio and video formats using standardized coding. To economize the design and to reduce redundancy in a multi-source system, it is expected that certain products may eventually omit their internal decoders in favor of providing their program content directly in digital form to a central decoding processor. Products may deliver Dolby Digital encoded bitstreams without the means to decode them internally into analog outputs. These products are referred to as Bitstream Source products. While this concept was introduced in the first format to deliver consumer Dolby Digital bitstreams—laser disc—this trend is expected to grow into other digital program sources such as DVD-ROM and various digital set-top products. Table 4.2 shows the data rates and sample rates for standardized Dolby Digital bitstreams, and for any optional Dolby Digital bitstreams. Table 4.2. Dolby Digital bitstreams available from existing Source products. Source Format
Sample Rate
Laser Disc DTV Digital Cable DVD
48 kHz 48 kHz 48 kHz 48 kHz
Standard Data Rate (max) 384 kb/s 384 kb/s 448 kb/s 448 kb/s
Optional Data Rate (max) — 448 kb/s — —
Laser disc is unique among Source products in that it is an established format already capable of delivering 2-channel audio from the original analog FM tracks (AFM), and also from the 2-channel 16-bit PCM digital audio tracks. Dolby Digital compatible laser disc players are able to provide both conventional stereo audio and Dolby Digital bitstreams without any internal
11 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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Dolby Digital decoder because both PCM tracks remain available, and because the Dolby Digital bitstream will usually represent the discrete multitrack version of the same soundtrack found in the PCM channels. Current LD players allow the user to select between AFM and PCM tracks and also between the left and right channels, which allows all available audio signals to come from a single pair of output jacks. Some LD players also provide a direct digital output for the PCM soundtrack in the S/PDIF format. To add Dolby Digital bitstreams in a way that preserves as much of the existing format as possible, the right channel AFM area carries the Dolby Digital RF signal. This RF signal has a separate output from the player for external decoding, and is demodulated into a standard Dolby Digital bitstream in the S/PDIF format for connection to Dolby Digital A/V decoders, as shown in the following diagram. L
PCM AUDIO DATA
2-CH D/A
L
FM1 RF
AFM DEMOD
FM2 RF
AC-3 RF OUT
AC-3 RF IN
AUDIO OUTPUTS
R
L
ANALOG/ DIGITAL AUDIO SELECTOR
R
R
AC-3 RF DEMOD
IEC 1937 (S/PDIF) FORMATTER
DIGITAL OUTPUT
OUTBOARD DEMODULATOR
Fig. 4.3. Basic laser disc player structure. Some A/V decoders may provide direct RF inputs and internal demodulators for laser disc sources to avoid the need for separate outboard demodulators. Some LD players may include the demodulator within the player itself as the cost of the demodulators falls over time.
4.4. Trademark and logo usage Products that are determined by Dolby Laboratories to meet the applicable design and performance requirements may display the Dolby logotype. The particular Dolby logo used depends on the basic audio functionality or the kinds of processing the product incorporates, and on consumer expectations. Each product is limited to the use of one main Dolby logo, except where products combine more than one category of licensed Dolby technology into a single unit, such as noise reduction and surround decoding. Dolby Digital and Dolby Pro Logic technologies will often be used together in the same product, and only one of these logos shall be displayed.
12 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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4.4.1 Usage guidelines for Dolby logo and trademarks on products As a general guide, Table 4.3 lists possible levels of Dolby technology that may be implemented in typical products, and the appropriate logo. See Part 12 for Virtual products, and Part 13 for personal computer product logo information. Table 4.3. Typical system logo usage. Number of Dolby Digital output channels
Additional Matrix processing
Applicable logo
Dolby Pro Logic
1 1 5 5 1
1 channel 2 channels
2 channels
Dolby Pro Logic
5.1 channels
Dolby Pro Logic
The main Dolby logo is not to be used as a mode indicator, but to show the source of specific technology incorporated in the product. The logo may be printed on the front panel, or illuminated by some means anytime the product is on. Dolby Surround Pro Logic products that allow field upgrading to Dolby Digital may also include this logo so it is ready to be illuminated, so long as it is not visible until the decoder upgrade has been installed. Once the Dolby Digital logo is activated, the Dolby Surround Pro Logic logo shall be permanently extinguished. It is not required, however, to replace the logos on field-upgraded decoders.
2
The trademarks “Dolby” and the “ ” may be used as necessary for switch and indicator markings. Dolby trademarks are not permitted for use in model numbers. See Part 9.3 for switch marking examples. 4.4.2 Trademark acknowledgment; license and copyright notice Licensed products must be marked on an exposed surface with the applicable notices. Owner’s manuals, service manuals, or product upgrade packages that include media (ROMs, EPROMs, ICs, disks, etc.) embodying licensed technology must carry the same notices. Only those trademarks actually used on the product need to be included in the notice. •
Products with Dolby Digital and Pro Logic: Manufactured under license from Dolby Laboratories. “Dolby”, “Pro Logic” and the double-D symbol are trademarks of Dolby Laboratories. Confidential Unpublished Works. 1992-1997 Dolby Laboratories, Inc. All rights reserved.
13 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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•
Products with Dolby Digital only: Manufactured under license from Dolby Laboratories. “Dolby” and the double-D symbol are trademarks of Dolby Laboratories. Confidential Unpublished Works. 1992-1997 Dolby Laboratories, Inc. All rights reserved.
Sales information for the above products displaying Dolby trademarks needs a trademark acknowledgment: •
Products with Dolby Digital and Pro Logic: “Dolby”, “Pro Logic” and the double-D symbol are trademarks of Dolby Laboratories.
•
Products with Dolby Digital only: “Dolby” and the double-D symbol are trademarks of Dolby Laboratories.
4.4.3 Laser disc players with Dolby Digital RF outputs Laser disc is an established format that might provide either digital or RF signals, so some additional wording is required on the front panel to identify when RF output connectors are present. It is recommended to use the same phrase as for the rear panel connector marking shown in Table 7.5 below to minimize confusion. Thus, LD players with only an RF output should state “Dolby Digital RF Out”. If the demodulator is built in, no additional wording is required. The following logo has been prepared for RF output laser disc players.
=
The laser disc player Dolby Digital RF logo:
Laser disc players, sales information, and owner’s manuals displaying Dolby trademarks requires a trademark acknowledgment. Only if the product or information displays the term “AC-3” shall the acknowledgment also include it: “Dolby”, “AC-3” and the double-D symbol are trademarks of Dolby Laboratories.
The product sales information and owner’s manuals for players with Dolby Digital RF Outputs need to state: This laser disc player provides a Dolby Digital RF Output for laser discs recorded with Dolby Digital soundtracks. Dolby Digital decoders with a Dolby Digital RF Input can accept this signal directly.
14 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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5.
Product specifications and requirements
Much in the tradition of other Dolby technologies, Dolby Digital will be applicable to a broad range of consumer products for decoding audio from standardized audio/video delivery formats. As such, it is necessary to define the use of Dolby Digital to ensure proper operation, and to promote good understanding among users. Since Dolby Digital is a system that goes well beyond the basic functions of coding audio into data and back again, its many user-oriented features will play a role in the convenience and utility of products that incorporate Dolby Digital. Product design issues fall into three main categories: requirements, recommendations, and options: •
Requirements relate to features, functions, and specifications that must be met in licensed products. These are generally rigid, and as such, must be set so as to allow the greatest range of products as possible to comply while still providing a meaningful benefit to the user. It is therefore the case that many licensed products exhibit performance that exceeds the published requirements by a significant margin, leading to a healthy diversity in the market among competing products.
•
Recommendations are made based on the intended uses and consumer expectations of the product. By way of the Licensee Information Manuals and related technical materials, similar design recommendations will be presented to all licensees making similar products. Due to the independent design considerations made by each manufacturer, diversity among competing products will again result.
•
Options are discussed for certain features or modes of operation based on what seems reasonable to do or because it is useful to let designers know a certain degree of freedom exists. No obligations are attached to these discussions.
The reader is cautioned that product requirements are described throughout this document. They appear in lists and tables, but also within the relevant text describing the design of licensed products. As used in this document, “must” or “shall” refer to mandatory requirements. “Should” refers to something that is recommended but not actually required. “May” refers to design options worthy of consideration, but no position is taken on their use or omission—that decision is left to the designer. Other words in this document may have the same meaning and carry the same weight, but these examples were cited as they have led to some confusion in the past. Every attempt will be made to be clear when requirements, recommendations, and options exist. If there is any question, please contact Dolby Laboratories.
15 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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6.
Product Groups and Standards
Licensed Dolby Digital products are designed for widely varying markets, and it would be inappropriate to expect them all to comply with a single standard. In order to apply standards consistent for a given product, three groups have been established: Group A, Group B, and Group C, as is traditional for other Dolby licensed products. These Groups help to identify performance or operational criteria that anticipates or agrees with general consumer expectations for the various products. There are also certain standards that apply to all product Groups in common. The purpose for establishing Product Groups is to improve communication between Dolby and its licensees regarding product design and performance. Dolby does not discuss Product Groups with consumers, and asks all licensees to do the same so that the issue of which Group a product falls into does not become a competitive factor in the marketing of the product. While this document covers a broad range of products with varying performance requirements, all are primarily designed to accept high-quality multichannel programs, such as from DTV, digital cable or satellite, DVD, or LD sources. The standard Dolby Digital audio coding mode for these sources is a 5.1-channel program at 384 kb/s, and a 48 kHz sample rate. When 2-channel programs are coded, the data rate will typically be 192 kb/s. All performance specifications are based on these data rates unless noted, and shall apply equally to 44.1 kHz and 48 kHz sample rates. Dolby Digital also supports 32 kHz sample rates, and this rate is generally required in licensed decoder products in the event that delivery formats should choose to adopt it.
6.1.
Definition of product Groups
Factors determining the appropriate Group are product type, design concept and execution, market price, and the projected image of the product through its cosmetic design, cost, or its promotional materials. Where it is not clear to which Group a product belongs, discussion between Dolby Laboratories and the licensee should resolve any classification difficulties. Dolby’s decision shall prevail in order to apply uniformity to all licensed products. 6.1.1 Definition and examples of Group A products Group A products represent not only the highest levels of performance available of their type, but also a high level of performance on an absolute basis. Certain product types may not apply to Group A classification at all, and, as with other products licensed by Dolby Laboratories, very few products may ever be required to meet Group A standards. Overall product audio performance is defined primarily by the capability of the licensed technology’s inherent characteristics, and is not limited by other aspects of the product. Examples are: • •
top-class consumer audio or audio/video outboard decoders top-class integrated amplifiers and control centers
16 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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6.1.2 Definition and examples of Group B products Group B products represent a wide range of popular consumer products, wherein a high standard of quality is expected, but not necessarily of the same uncompromised level as Group A. Examples are: • • • • •
•
most audio or A/V integrated amplifiers, receivers, control centers, and outboard decoders high-end televisions, either stereo or surround equipped high-end satellite receivers and cable receivers, DVD players, or other “set-top” boxes personal headphone products premium or high-end car systems entertainment PCs (for home A/V system application)
6.1.3 Definition and examples of Group C products Group C products are expected to function properly, produce sound free of distracting defects, and are aimed at fulfilling basic functional requirements rather than particular excellence in sound quality. Within their markets, they nonetheless represent good performance relative to similar technologies or products with similar utility. Examples are: • • • • •
•
6.2.
basic satellite receivers and cable receivers, DVD players, or other “set-top” boxes consumer VCRs and audio recorders basic to mid-level televisions, either stereo or surround equipped basic to mid-level car audio systems most battery operable portables multimedia PC products (for business or personal use)
Definition of product Standards
It is important that products with Dolby technologies and trademarks be perceived as high quality products. Because consumers may be most concerned with the overall performance and operation of a product, Dolby Laboratories evaluates products in the following basic areas in order to more closely determine that each is meeting the expected requirements. • • •
accuracy of implementation and performance of the licensed technology presence and functionality of the required inputs, outputs, features, and markings overall subjective operation and sound quality
Evaluation samples will be tested with respect to the applicable performance standards of their Group. However, it should be noted that the performance of the submitted sample should exceed the applicable specifications by a comfortable margin in order to ensure that production unit variations will not cause units to fall below the limits.
17 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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6.2.1 Standards for all product Groups a.
Approved implementations. The Dolby Digital and Pro Logic decoding algorithms shall have been approved separately by Dolby Laboratories before the product using them can be approved. Note: It is sometimes necessary to design products with ICs that have not been completely developed or that have not yet been approved by Dolby. To do so is entirely at the product designer’s risk. Dolby cannot assure when or if any given implementation shall be approved, or that it shall be manufactured by a certain time.
b.
Bitstream compliance. Decoder products shall generally be required to accept the full range of Dolby Digital bitstream parameters (e.g., sample rates, data rates, audio coding modes) as defined in the ATSC A/52 document, with the exception of the 32 kHz sampling rate where the maximum data rate to be supported shall be limited to 448 kb/s. Typical DTV and DVD decoder products need only support 48 kHz sampling and a maximum of 448 kb/s data rates. Decoder products are not required to handle 1+1 mode audio programs (dual mono). Source products shall be designed to accept all bitstream data rates and sampling frequencies allowed by the applicable delivery formats. Certain Source products (set-top cable and satellite receivers and DTV receivers) may need to support the 1+1 mode if adopted by the broadcast industry.
c.
Line outputs in Source products. Source products are not required to provide audio line outputs when other outputs suitable to the market are provided, such as mono RF remodulators in cable receivers, or headphone jacks on personal portable products. If line outputs are provided, it is recommended they have fixed audio levels. Volume controlled line outputs may be provided in addition to fixed outputs. Variable line outputs may also be used in place of fixed outputs if the following provisions are met:
d.
•
The audio output level defaults to a reference output level at power-up, as detailed in (d) below.
•
The user can set the output to this calibrated level directly, e.g., via a command on the remote control or via a menu selection.
Reference output level. As a reference, 2-channel signals to a Dolby Digital encoder 20 dB below full scale (-20 dBFS) with dialog normalization set at –31, shall give between 100 and 200 mVrms at a Source product decoder’s fixed or calibrated variable line outputs. Fixed output levels must not exceed 2 Vrms under any output, downmix, or bass redirection condition. Balanced outputs may provide up to 6 dB more output measured differentially. Outboard processors (Part 11) shall meet these same requirements. A master output trim with limited range (≤12 dB) may be provided to compensate for signal build-up due to downmixing or bass redirection, or to better match levels among the various signal sources.
18 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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e.
Input level requirements. Line inputs must be able to accept 2 Vrms audio signals without overloading any stage before the volume control at any frequency. This shall be possible no matter what audio processing is being performed on these signals, such as surround decoding, soundfield recreation, dynamic compression, or tone/equalization. Fixed line input levels will be referenced to 200 mVrms for test purposes. Variable line inputs shall provide an overload indicator. PCM inputs will be referenced 20 dB below digital full scale for testing purposes. The decoder must not overload at any stage before the volume control at any frequency with signals in all channels at -3 dBFS simultaneously. This shall be possible no matter what audio processing is being performed on these signals, such as surround decoding, soundfield recreation, dynamic compression, bass redirection or tone/equalization.
f.
Audio processing. Decoded audio outputs shall reflect dynamic range compression as provided by dynamic range and/or compression words in the bitstream information, as appropriate. Dynamic range control may be user defeatable or variable, with the preferences able to be set and stored. Decoded audio outputs shall also reflect dialog normalization in response to received bitstream information. Dialog normalization must not be user defeatable.
g.
Output requirements on Source products. A standardized S/PDIF (IEC 1937) Dolby Digital output shall be provided on all 2-channel Dolby Digital Source products, such as receivers of digital transmissions (TV, cable, satellite), or players or recorders of discs, tapes, or other magnetic or memory-based media. The internally decoded audio output of a Source product is assumed to be synchronized with the picture. With the internal audio as the reference, the audio generated by an external reference Dolby Digital decoder fed from the Dolby Digital IEC1937 bitstream output shall be synchronous with the internal audio within +5 to –15 ms. Portable products are generally not required to provide a digital output. Laser disc players may substitute an RF Dolby Digital output to meet this requirement, as described in Part 7.4. The S/PDIF Dolby Digital output should remain active full time. It may be user switchable to PCM.
h.
Output requirements on Decoder products. A standardized S/PDIF (IEC 1937) Dolby digital input shall be provided for all Dolby Digital decoder products, such as control centers, amplifiers, receivers, or outboard decoders. Portable products are generally exempt from this requirement.
i.
Nominal channel matching. All speaker and line level outputs shall have identical output voltage levels when the output balance and trim controls are in the center positions of their range, given equal input signals in each channel, ±1 dB. Fixed or level-ganged multichannel outputs shall match to within ±0.5 dB between the worst case pair of outputs. Individual level trim controls shall provide a symmetrical boost and cut of ±10 dB in steps of 1 dB or less. Products that provide all amplifiers and speakers and have no variable line outputs may reduce the boost/cut trim range to ±6 dB, and shall be designed to match their acoustic output levels rather than the power amplifier output voltages. Conventional leftright output balance controls which operate in both channels at once must not exceed
19 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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0.5 dB per step in each channel. If only one channel changes gain while the other remains fixed, 1 dB per step is acceptable. Balance controls shall have a minimum range of ±6 dB. Refer to Part 7.2.2 for further details. j.
Output gain. Variable line outputs in products that provide amplified speaker outputs shall attain matching speaker output levels within ±5 dB when driving external power amplifiers having a fixed gain of 29 dB without any use of the decoder’s internal gain trim controls. Example: If the left channel power amplifier produces 1 W into 8Ω (2.83 Vrms), the center channel line output shall provide 100 mV ±5 dB from the same input signal level, with the center level trim set to the center reference position.
k.
Headphone outputs. Headphone output jacks must maintain subjectively equivalent standards of quality as the main product outputs.
l.
Multichannel reproduction capability. Products shall reproduce and/or downmix any received signals to accommodate the audio outputs available on the product. Multichannel products shall also include support for basic listening modes: main L/R outputs only; operation without a center speaker; operation without surround speakers.
m. Signal polarity. Absolute polarity of audio signals shall be maintained on all audio outputs. n.
Decoder processing margin. Decoders will be required to provide sufficient processing margin to ensure that applicable “worst case” Dolby Digital bitstreams may be properly decoded. While this requirement will usually be covered by the qualification of the decoder IC, some ICs allow additional programming to be added that could encroach on the processing capacity or memory, and thus could result in reduced decoding ability.
o.
Wireless outputs. RF and infra-red (IR) outputs for wireless surround speakers shall be tested to the same requirements as speaker outputs. RF and IR headphone outputs will have relaxed requirements as long as a conventional headphone jack is offered.
p.
Test signal interface. Test points shall be incorporated as separately prescribed to ease the injection or detection of digital audio bitstreams for testing purposes.
q.
Surround channel time delay: •
Dolby Digital: 0–15 in 5 ms steps (max). Default 5 ms.
•
Pro Logic: 15–30 ms in 5 ms steps (max). Default 20 ms.
•
One setting controls both Dolby Digital and Pro Logic with fixed 15 ms offset.
20 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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r. Listening tests. Dolby will perform listening tests on the audio outputs to determine that they meet basic standards of quality. A primary concern is the intrusion of hum, buzz from the video, or other noise or impairments to the audio that would disturb listeners over a long period of time. s. Decoder adaptability. Decoders will be required to accept contiguous bitstreams which change the number of audio channels or program data rates without causing audible errors in decoding such as loud bursts of noise or other clearly undesirable effects. A short mute/unmute cycle is acceptable, as long as the audio returns in less than 500 ms. t. Decoder error handling. Decoders shall be able to accept any illegal data streams, then begin to play normally one valid bitstreams are again present, automatically. u. Copy control information. Systems which incorporate digital interfaces which can carry Dolby Digital (AC-3) bit streams, or linear PCM audio derived from Dolby Digital bit streams, shall respect any copy control information which is present on any source media which provide the bit streams. In particular, in the case of an IEC 958 / IEC 1937 output from a DVD player, the CGMS data shall be translated to SCMS data to provide the same level of copy protection (free-copy, one-copy, no-copy) to the audio transmitted over the digital interface. Refer to Parts 7.1.6 and 7.1.9 for additional details. 6.2.2 Standards for Group A products All functional and performance attributes of the Dolby technology and of the user interface (mode switches and indicators) are to be implemented for the best advantage. a. b. c. d. e. f. g. h. i. j. k.
Group A Dolby Digital decoder IC required (20-bit data from Dolby Digital decoder). D/A converters with ≥20 bit capability. S/N: 75 dB CCIR/ARM relative to –20 dBFS. Headroom: 20 dB relative to –20 dBFS. Frequency response: ±0.5 dB 3 Hz to 20 kHz when source program allows. Distortion: to be determined. Center delay required: 0 to 5 ms in 1.0 ms steps. Default setting: 0 ms. Output Configurations 1, 2, and 3 supported when ≥3 outputs are provided. See Part 9.8. Master volume control tracking: ±1.0 dB between any channels over top 50 dB range. All variable line outputs shall be capable of delivering at least 3 Vrms without clipping. Products with internal amplifiers also provide standard line outputs for all channels.
21 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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6.2.3 Standards for Group B products The product incorporates a reduced, yet appropriate, set of functional and performance attributes of the Dolby technology and of the user interface (mode switches and indicators), implemented for the best advantage. a. Group A or B Dolby Digital decoder IC must be used (≥18-bit data from Dolby Digital decoder). b. D/A converters with ≥18 bit capability. c. S/N: 65 dB CCIR/ARM relative to –20 dBFS. d. Headroom: 20 dB relative to –20 dBFS. e. Frequency response: +0/–1 dB 20 Hz to 20 kHz when source program allows. f. Distortion: to be determined. g. Center delay required: 0 to 5 ms in 1.0 ms steps. Default setting: 0 ms. h. Output Configurations 1 and 2 supported when ≥3 outputs are provided. See Part 9.8. i. Master volume control tracking: ±2.0 dB between any channels over top 50 dB range. j. All variable line outputs shall be capable of delivering at least 2 Vrms without clipping.
6.2.4 Standards for Group C products The product incorporates a minimum set of functional attributes of the Dolby technology and the user interface (mode switches and indicators), exploited for best advantage. a. b. c. d. e. f. g. h. i. j.
Any approved Dolby Digital IC may be used (≥16-bit data from Dolby Digital decoder). D/A converters with ≥16 bit capability. S/N: 55 dB CCIR/ARM relative to –20 dBFS. Headroom: 20 dB relative to –20 dBFS. THD + N ≤0.2% relative to 0 dBFS. Frequency response: +0/–3 dB 20 Hz to 20 kHz when source program allows. Interchannel phase ≤5°. Output Configurations 1 and 2 supported when ≥3 outputs are provided. See Part 9.8. Master volume control tracking: ±3.0 dB between any channels over top 40 dB range. All variable line outputs shall be capable of delivering at least 1 Vrms without clipping.
22 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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7.
General product design considerations
This section discusses basic design features relevant to all products, such as audio connections, level controls, and audio processing features of Dolby Digital. Information on the design of compatible laser disc players and video software is included.
7.1.
Product input and output connections, copy control
An assortment of connector types are used for input and output signals. Many follow industryestablished standards, while others have certain policies or recommendations from Dolby pertaining to their use. The following summarizes the main connector types and their basic characteristics. Systems which incorporate digital interfaces which can carry Dolby Digital (AC-3) bitstreams, or linear PCM audio derived from Dolby Digital bitstreams, shall respect any copy control information which is present on any source media which provide the bitstreams. In particular, in the case of DVD, the CGMS data shall be made available over the digital interface. 7.1.1 Line input and output design Surround decoders and control centers provide stereo phono input connectors for various audio or audio/video sources. Other classes of products for specialized applications such as computers may use different connectors, such as mono or stereo mini phone jacks. If input level controls are provided, a level indicator is required to inform the user if a signal overload condition exists. Line outputs may be variable or have fixed levels depending on the application. Just as video recorders and video disc players avoid volume controlled line outputs, the same will be the case for other Source products such as satellite and cable receivers. Line outputs are primarily intended for recording or connection to an external stereo or surround audio reproduction system, not for direct connection to a power amplifier, and thus should have fixed audio outputs at standardized audio levels. RCA phono type connectors are assumed unless special circumstances dictate otherwise. 7.1.2 Balanced audio connections Certain high-end audio equipment provides balanced audio connections. In the professional world, 3-pin “XLR” connectors are the standard, and these and other types have found their way into some consumer products. Dolby accepts the use of XLR connectors in licensed consumer products. In accordance with IEC standards, pin 2 is the positive or “hot” pin. 7.1.3 Multichannel connections Multichannel audio inputs and outputs, whether carrying single-ended or balanced audio, may be provided using a DB-25 interface standard established by Lucasfilm Ltd. for Home THX ® products. As this provides high space efficiency on products often running short of panel space,
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it is becoming popular for multichannel A/V processors and power amplifiers. It is finding new use as the interconnect between outboard Dolby Digital decoders and A/V receivers.
Table 7.1. Unbalanced DB-25 pin assignments. 1
13
14
25
Pin 1 2 3 4 5 6 7, 8 9, 10 11 12 13
Assignment Left positive Center positive Right positive Subwoofer positive (or L sub) Left surround positive Right surround positive Reserved (optional R sub) Shield drains Remote trigger C Reserved Remote trigger A (power)
Pin 14 15 16 17 18 19 20, 21 22 23 24 25
Assignment Left ground Center ground Right ground Subwoofer ground Left surround ground Right surround ground Reserved Shield drain Remote trigger C ground Logic ground Remote trigger A ground
Table 7.2. Balanced DB-25 pin assignments. 1
13
14
25
Pin 1 2 3 4 5 6 7, 8 9, 10 11 12 13
Assignment Left positive Center positive Right positive Subwoofer positive Left surround positive Right surround positive Reserved Shield drains Remote trigger C Reserved Remote trigger A (power)
Pin 14 15 16 17 18 19 20, 21 22 23 24 25
Assignment Left negative Center negative Right negative Subwoofer negative Left surround negative Right surround negative Reserved Shield drain Remote trigger C ground Logic ground Remote trigger A ground
Input connectors shall be female and output connectors male per standard industry practice. Remote trigger A signals when power has been turned on in the decoder product. It is suggested that a delayed +5V signal be presented from the main decoder/controller that can tell the outboard Dolby Digital decoder to power itself on. Remote trigger C is undefined and unused. Phono connectors may alternatively be used for multichannel audio connections. The multichannel audio signal levels and balance relationships must meet certain requirements to prevent overload and to ensure proper sound balance, as described in Part 6.2.1 d and i. Also see Part 9.10.2 for further information.
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7.1.4 Color coding output connections The connectors themselves are left to the discretion of the product designer. Color coding, however, is becoming more prominent to help identify channels. If colors are to be adopted, it is suggested to use ones already established by the industry. There are currently two in wide usage. Table 7.3 describes colors established by Lucasfilm Ltd. for Home THX® products. A handy memory method for the channel color assignments would be to recall that RGB is a popular acronym in video, and that red always refers to Right. RGB are thus the three important colors (red, green, and blue) that stand for Right, Center, and Left, respectively. Table 7.3. Proposed color codes for multichannel audio connections. Channel
Color
Left Center Right Left Surround Right Surround Subwoofer
blue green red blue/white (see notes) red/white (see notes) brown
Pantone Code 300 354 185 300 185 4635
•
Note 1. For speaker terminals on power amplifiers, the positive (output) terminals would follow the color code in Table 7.3, with the negative (ground return) terminals would be black in every channel. The surround output connections would have a white background area painted on the chassis to distinguish them from the other connectors mounted on a typically black chassis.
•
Note 2. For RCA phono line inputs or outputs, the colors in Table 7.3 would be found on the connector itself, such as a stripe around the base, or may be applied to the chassis insulators behind each connector. The two surround connectors use the same colors as their respective front outputs, but the panel behind the connector would be painted white to distinguish them from the other connectors mounted on a typically black chassis.
The EIAJ has a color coding standard (CPX-1220) for HDTV 4-channel audio, which we have informally extended to cover stereo surrounds and a subwoofer as in Table 7.4. Table 7.4. Alternative proposed color codes for multichannel audio connections. Channel Left Center Right Left Surround Right Surround Subwoofer
Color white gray red black/white black/red brown
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The colors chosen should be based on what will be the least confusing to the consumer, and this may be affected by which color system (if any) may already be in use on other products in the system or the country where the equipment is sold. 7.1.5 Headphone output connections Industry standard 1/4”, mini, or micro phone jack connectors will typically be used. Headphone outputs require a volume control, even in “fixed” output products. 7.1.6 S/PDIF Dolby Digital and PCM digital interface The consumer version of IEC 958 is commonly known as S/PDIF (Sony/Philips digital interface). To extend the use of IEC 958 to carry coded digital audio signals, IEC 1937 was adopted. For reasons of consumer convenience and lower cost interconnects, the digital inputs and outputs are recommended to be direct electrical connections using conventional phono connectors. Optical connectors may be used if preferred or advantageous for reducing radiated energy. The IEC 1937 output may also be used for conventional PCM digital audio signals with up to 20-bit data. Whenever S/PDIF outputs on Source products or outboard processors carry PCM audio derived from Dolby Digital signals, dialog normalization shall be performed. The sampling rate of the incoming data in the S/PDIF bitstream defines the sampling rate of the D/A converters, and hence the PCM output in the S/PDIF format. Decoders with IEC 1937 inputs generally need to accept any of the three standard sampling rates, 32, 44.1, and 48 kHz. Specific products based on DVD or DTV standards may only need to support the relevant data rates. Source products will not provide IEC 1937 Dolby Digital inputs, and therefore need only operate at the data rates supported by the format itself. Copy control information The following bits (within the range of bit 0 to bit 15) of Channel Status information shall be properly set as shown in Table 7.5: Table 7.5. Setting Channel Status bits. CS bit 2 8-14 15
Meaning Copyright Category code (for DVD '1001100') L bit
Table 7.6 shows the mapping between the CGMS bits on DVD and the proper setting of bits 2 and 15 of channel status.
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Table 7.6. Mapping DVD CGMS bits to IEC 958. CGMS bits 0 0 1 1
0 1 0 1
IEC 958 bits 2 15 1 x - 0 0 0 1
Meaning Unrestricted copy OK Not used One generation copy allowed No copying permitted
x = don’t care
7.1.7 RF transmissions for wireless speakers It is increasingly popular to use RF transmissions to eliminate surround speaker wires or to ease remote listening. It is recommended that the system volume control for that channel be placed in the receiver unit to maintain good dynamic range at all playback levels. This is not always practical, however, so it is important to design the system with great care to ensure sufficient sound quality is maintained. The same applies to infra-red transmission of audio for headphones. Dolby noise reduction may be useful in these applications. 7.1.8 Dolby Digital RF carrier inputs and outputs A phono connector is used on laser disc players to deliver the proprietary Dolby Digital RF signal found on compatible Dolby Digital laser discs. A special RF demodulator is required to recover the digital information and ensure it meets Dolby Digital specifications. This demodulator may be provided in the laser disc player itself; in a stand-alone demodulator box; or in an outboard Dolby Digital decoder, integrated surround receiver, or control center. Providing an Dolby Digital RF input and demodulator inside an Dolby Digital decoder or receiver does not take the place of the required IEC 1937 Dolby Digital input. Table 7.7 shows the preferred markings for output connectors on Dolby Digital bitstream Source products. Table 7.7. Preferred names for bitstream source connector types. Connector type S/PDIF type connector RF type connector S/PDIF including PCM
Marking Dolby Digital Out Dolby Digital RF Out PCM/Dolby Digital Out
7.1.9 USB, IEEE 1394 outputs PC products are often equipped with USB (universal serial bus) digital outputs. These ports are capable of delivering the Dolby Digital bitstream. In certain cases, it may be necessary to provide a “dongle” or in-line converter to create an S/PDIF output.
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Copy control information Interfaces such as Universal Serial Bus and IEEE 1394 have their own methods for signaling copy protection information. Systems shall communicate the CGMS data over these interfaces by using the appropriate facilities.
7.2.
Controlling output levels
The usual way to control audio output levels is with a volume control. With Dolby Digital, program volume may also be controlled automatically to achieve uniform listening levels or calibrated reference reproduction levels. There are further audio alterations possible with Dolby Digital relating to dynamic range. Audio compression may be applied in a fixed degree, or it may be varied manually or in response to changes in the setting of the volume control to improve intelligibility at all listening levels. These features are discussed below. 7.2.1 Master volume control This control varies all output signals simultaneously. It is essential to maintain close level tracking between all sections over the useful range of the control. Additional audio functions, such as loudness compensation, must not alter the relative channel balance over the range of the control. If a volume control is provided in the line output path, the control should be placed after the D/A converter to avoid increasing quantization noise at low volume settings. If it can be demonstrated that a volume control placed before the D/A can operate without introducing audibly degrading side-effects, it may be implemented in this manner upon confirmation at Dolby Laboratories. This is only likely to be possible in products that incorporate power amplified outputs, such as televisions or portable products. Besides the need to maintain good level tracking, the volume control may be used for dialog normalization or other system program level management duties. For these reasons, electronic controls with uniform 1 dB maximum step attenuation over the range is recommended. Mechanical controls, especially multichannel units, may not have very good gain matching over their range, and cannot be operated “invisibly” by the system controller. There must be sufficient system gain to allow programs to reach full playback loudness with typical amplifiers and speakers without having to advance the volume control close to its maximum position. With a reference signal from a main audio channel at –20 dBFS and dialog normalization at –31 (no attenuation), the nominal line output required to reach full listening level will be near 150 mVrms. Reserve gain is necessary so that low level programs may also be used. This will typically imply a line amplifier of about 10 dB gain, such that the reference signal may reach at least 500 mV at full volume. 7.2.2 Gain trims, balance controls It is required that products enable the user to match all speaker levels for proper sound balance. In audio systems, it is necessary to compensate for different amplifier gains, speaker efficiencies, and room acoustics. Most products allow the main left and right channels to be matched with a conventional balance control. It is then only necessary to provide level trims for any additional
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outputs to bring them to the same level. Subwoofer outputs are optional, but if present they are recommended to include level trim controls in case the subwoofer amplifiers have no gain controls. A typical “level/balance” menu might offer these kind of adjustment options: Table 7.8. Suggested names for level controls. Option 1 L Level C Level R Level RS Level LS Level SW Level
7.3.
Option 2 L/R Balance C Level RS Level LS Level SW Level
Option 3 Main Balance Center Level Rear Level Rear Balance Sub Level
Audio features of Dolby Digital
Dolby Digital decoders will be able to tailor audio reproduction to the specific needs of the user through built-in features of the delivery and reproduction system. Audio programs will originate with the full degree of spatiality and dynamic range desired by the producers. When programs are reproduced with fewer channels or at reduced listening levels, or through products with limited dynamic range, it is important to preserve as much of the program content and original artistic intent as possible. The downmixing and dynamic range compression features of Dolby Digital aid in this task. A “dialog normalization” feature helps unify the subjective listening level of all programs. Consumers receive audio/video signals from a variety of sources. Traditionally based on analog methods, audio signals are often normalized to their peak values to maximize the signal-to-noise ratio through transmission and recording media. In order to ensure that programs maintain similar subjective loudness, those with greater dynamics have to be compressed to sound more like those with lower dynamic range (high average loudness). This forces all programs to have relatively little dynamic contrast, which does not always best serve the art. Digital formats are changing the way programs are recorded because it is no longer difficult to maintain signal quality through transmission and storage media. CDs, laser discs, and even VHS Hi-Fi tapes are able to maintain high dynamic range with ease. All are used to deliver programs with peak signal levels some 10 to 20 dB above their normal reference levels. When these programs are compared with the higher density of conventional television broadcasts, they may sound as though they are recorded at a lower volume. In fact, the unlimited program may have signal peaks which far exceed those of the subjectively louder program.
29 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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LD MOVIE
VHS Hi-Fi MOVIE
DSS PREMIUM MOVIE
CD CLASSICAL MUSIC
CD POPULAR MUSIC
TV BROADCAST
+20 dB
+10 dB
0 dB
-10 dB
-20 dB
Fig. 7.1 Typical audio levels from various consumer signal sources. 0 dB = 200 mVrms. Fig. 7.1 compares typical program levels from various sources. The heavy marker represents the average program loudness level, and the lightly shaded area represents the maximum signal headroom available above that point. The maximum outputs do not exceed about 2 Vrms from consumer sources, with TV broadcasts having the lowest headroom. 7.3.1 Dialog normalization If one were to listen to each of the program sources in Fig. 7.1, not only would the dynamics differ among them, but so would the apparent loudness. The only remedy available to consumers is to readjust the listening volume each time the source is changed. Additionally, this may be necessary even with a single source, such as when switching from CD to CD, for example, or when a television broadcast transitions from the main program to a commercial or news program. The dialnorm variable in the Dolby Digital bitstream describes the average dialog level of that program. When dialog normalization is applied, the overall program gain may be changed from just a few decibels to as much as 12 dB or more for the course of the entire program, allowing all programs to be reproduced at the same subjective loudness, i.e., with the same average dialog level. Large changes in loudness between different sources and programs can easily be avoided. This makes it possible to create a listenable program channel comprising a wide variety of soundtrack production styles. Fig. 7.2 shows these same program sources normalized for equal listening volume. The reproduction levels have been adjusted by some 10 to 12 dB, essentially to attenuate the “densest” programs to match the subjective loudness of the least compressed ones.
30 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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LD MOVIE
VHS Hi-Fi MOVIE
DSS PREMIUM MOVIE
CD CLASSICAL MUSIC
CD POPULAR MUSIC
TV BROADCAST
+20 dB
+10 dB
0 dB
-10 dB
-20 dB
Fig. 7.2. Audio levels normalized for equal loudness. 0 dB = 200 mVrms. 7.3.2 Dynamic range control There are two variables within the Dolby Digital bitstream, dynrng and compr, that provide automatic gain control in the decoder based upon information developed during the Dolby Digital encoding process. Dynrng provides dynamic range compression useful for situations such as late night viewing of programs with a wide dynamic range (that might otherwise disturb the neighbors) or for program material that needs significant compression to improve coverage and intelligibility. Dynrng also provides the necessary peak limiting required to avoid signal overload when downmixing to as few as one output channel. Compr provides additional peak limiting to allow the average program level to be increased. This boosts the apparent loudness without increasing the possibility of overmodulation, which is useful when passing the audio through an RF remodulation path having limited headroom. The dynamic range function of Dolby Digital is able to provide sufficient gain reduction to allow even high dynamic range soundtracks to maintain good audibility at low volume levels. A certain minimum amount of dynamic range reduction will be automatically included in the bitstream to ensure safe downmixing, the amount of which depends on the setting of the dialnorm variable and on the contents of the audio channels themselves. Additional compression may be applied by the engineer preparing the soundtrack if so desired. The amount of compression heard upon reproduction may vary from none at all to the full amount, depending on how the decoder is being used. To obtain the full effect of the dynrng variable, the scaling coefficient is 1.0. To reduce the effect, the scaling coefficient may be reduced from 1.0 to 0.0. Scaling by 0.0 defeats compression. To obtain equal decibel changes in the effect, equal step sizes in the scale factor should be used. For example, steps of 0.0, 0.5, and 1.0 , or a continuously variable factor with a linear control law. 7.3.3 Downmixing audio Whenever the number of decoder outputs is less than the number of channels in the Dolby Digital program, downmixing is required. The decoder may change the downmixing process 31 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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based on the number of speakers in the system, or on the number of audio outputs needed, say, for headphone listening. Stereo and mono downmix ratios can be altered somewhat by the producers to ensure optimum results without compromising the multichannel balance. This is accomplished by using optional variables in the Dolby Digital bitstream (clev, slev) which represent different mixing coefficients for the center and surround channel signals, respectively. A surround compatible Lt/Rt downmix may also be provided, but in this case the downmix coefficients are fixed. Table 7.9 summarizes the downmix options. Product designers need to choose the output configuration(s) appropriate for the specific application. Table 7.9. Output configuration options. Output Configuration 1/0 2/0 Lo/Ro 2/0 Lt/Rt 2/1 2/2 3/0 3/1 3/2
Downmix method uses clev and slev when present uses clev and slev when present fixed downmix coefficients not applicable uses clev when present uses slev when present not applicable no downmix needed
Note that the 2/1 and 3/1 output configurations are not considered valid or necessary, and should not be used under any circumstances. All Dolby Surround systems use at least two surround speakers even though the surround signal has previously been only mono. Now that stereo surround signals are available in Dolby Digital source programs, it is only necessary to support 2-speaker surround outputs from the decoder. 7.3.4 Operational modes To ease the design of decoder products, Dolby Digital ICs offer standard operating modes called “Line Mode” and “RF Mode”. These modes are included within the Dolby Digital decoder IC itself, thus greatly simplifying the implementation of dialog normalization, dynamic range control and downmixing functions, all of which are necessary in Dolby Digital products. Two “Custom Modes” offer additional design flexibility aimed at more esoteric audio products where additional implementation cost and complexity are not of primary concern. Line Mode Summary of Line Mode features: • dialog normalization always on • dialog reproduced at a constant level (–31 dBFS) • dynrng compression variable used • low-level boost compression scaling allowed • high-level cut compression scaling allowed if not downmixing
32 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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The Line Mode is applicable in the widest range of products due to its flexibility and ease of use. All line level or power amplified outputs from 2-channel set-top decoders, 2-channel televisions, 5.1-channel televisions, A/V surround decoders, and outboard Dolby Digital adaptors should be derived from this mode. Figure 7.3 shows the signal relationships of the Line Mode under different conditions. Note that whether or not downmixing or compression are active, the average program loudness remains constant. 5.1-CH MOVIE W/ DIALNORM
5.1-CH W/ VARIABLE COMPRESSION
5.1 TO 2-CH DOWNMIX
+20 dB
+10 dB
MIN HIGH LEVEL COMPRESSION MAX
0 dB
-10 dB
DIALOG
DIALOG
-20 dB
-30 dB MAX -40 dB
LOW LEVEL COMPRESSION
-50 dB
MIN
Figure 7.3. Signal relationships in the Line Mode. RF Mode Summary of RF Mode features: • dialog normalization always on • dialog reproduced at a constant level (–20 dBFS) • dynrng and compr compression variables used • compression scaling not allowed • +11 dB gain shift imposed This mode is optimized for products generating a downmixed signal for subsequent “channel 3” RF remodulation. The overall program level is raised 11 dB, while the peaks are limited to prevent signal overload in the D/A converter. By limiting headroom to a maximum of 20 dB above average dialog level, overmodulation of television receivers is prevented while providing an average RF modulation level that compares well with quality television broadcasts and premium movie channels. Fig. 7.4 shows the signal relationships of the RF Mode under different conditions. Note that whether or not downmixing is active, the average program loudness remains constant. Compression remains fully on at all times.
33 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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5.1-CH MOVIE W/ DIALNORM +20 dB
+10 dB
0 dB
-10 dB
5.1 TO MONO DOWNMIX
VALID PEAK OUTPUT RANGE DIALOG
+11dB GAIN SHIFT
-20 dB
-30 dB
MAX LOW LEVEL COMPRESSION
-40 dB
-50 dB
Fig. 7.4. Signal relationships in the RF Mode. See Fig. 7.5 for an example of how signals generated with the RF and Line Modes can relate to the modulation index of a typical RF remodulator circuit. While Line Mode may be used for this purpose, the improvement in program dynamics will come with a lower average loudness compared with other television signal sources. RF OUTPUT MODE 5.1 TO MONO DOWNMIX +20 dB
200%
+14 dB
100%
+8 dB
50%
0 dB
20%
-6 dB
10%
-11 dB
6%
-16 dB
3%
LINE OUTPUT MODE 5.1 TO MONO DOWNMIX
DIALOG
DIALOG
RF MOD MAX LOW LEVEL COMPRESSION MAX LOW LEVEL COMPRESSION MIN
Fig. 7.5. RF remodulator signal levels.
34 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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Custom Modes There are two Custom Modes, 0 and 1. Essentially, the Custom Modes defeat some or all of the features of the Line and RF Modes, thus shifting the burden to the product designer for implementation elsewhere in the audio path. No products are required to use the Custom Modes. If they are used, the dialog normalization, dynamic compression and downmixing functions must still be provided in the final product. Summary of Custom Mode 0 features: • dialog normalization always off • –11 dB gain shift imposed when downmixing to prevent peak level overload • dynrng compression variable used • low-level boost compression scaling allowed • high-level cut compression scaling allowed Dialog normalization must be implemented in the analog circuitry—usually in the master volume control—under control of the dialnorm variable in the bitstream. No changes in the position of the volume control should be visible to the user when dialog normalization operates. Custom Mode 1 is the same as Custom Mode 0 except it provides the dialog normalization function internally. Note that one of the conditions of the Line Mode is that full high-level compression is applied whenever downmixing is active, so its effect cannot be reduced. Both Custom Modes allow the degree of compression applied to be scaled down or defeated under any condition. The only restriction is that when downmixing is active, a –11 dB gain shift is imposed to ensure no signal overload will occur. Products using the Custom Modes require +11 dB of selectable gain correction after the D/A converter to compensate for this. One consequence is that the final audio outputs may exhibit a higher noise floor under this condition.
35 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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5.1-CH MOVIE W/O DIALNORM
5.1-CH W/ VARIABLE COMPRESSION
5.1 TO 2-CH DOWNMIX W/ COMPRESSION
MIN HIGH LEVEL COMPRESSION MAX
+20 dB
+10 dB
0 dB DIALOG
-11dB GAIN SHIFT
-10 dB
-20 dB
DIALOG
-30 dB MAX -40 dB
LOW LEVEL COMPRESSION
-50 dB
MIN
Fig. 7.6. Signal relationships in Custom Mode 0. 7.3.5 Using operational modes in products More than one operational mode may be used in a given product. Furthermore, these modes may be applied in different ways depending on the type of product involved. For example, Table 7.10 shows how two operational modes might be used in basic set-top boxes or televisions. Table 7.11 shows three typical listening modes that might be found in more elaborate home theater systems. A set-top box (cable or satellite receiver, or DVD player) or basic digital television needs the ability to conform its audio to traditional signal references, such as VHS Hi-Fi tapes or broadcast television signals. The Standard mode in Table 7.10 (and 7.11) results in audio signals with good dynamic range, much like a prerecorded VHS Hi-Fi movie. This may be the mode of choice for people who connect the audio to a Dolby Surround Pro Logic system, for example. There may be others who feel the average loudness of the signal is too low when switching between digital programs and regular television programs, or that the loud portions of the digital program are too high compared with the average dialog level. In this case, the Compressed mode will raise the average loudness of the dialog and restrict the program peaks much in the style of conventional television audio. It is expected that the option to switch between these two listening modes will be a “one time” event when the system is installed, chosen based on the user’s preferences or on the capabilities of the rest of the system used with the set-top box. The actual nomenclature is a matter of choice based on the product’s user interface design, or to best address the expected users of the product.
36 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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Table 7.10. Examples of listening modes in a set-top box. Listening mode Standard Compressed
Description
Mode
normal dynamic range full compression
Line RF
Gain correction required none none
Compression scaling (high/low) 1.0/1.0 1.0/1.0 fixed
A home theater product may offer the user the option to alter the reproduced dynamic range more freely, so the sound may be optimized for changing listening situations or user preferences. For this reason, it is suggested that three basic modes be offered. The average loudness of the program should not change when switching among Late Night, Standard, or Maximum modes. In Late Night, the RF mode is activated but the automatic 11 dB boost must be canceled by applying -11 dB gain correction. The Standard mode is exactly as explained previously, but in this case the product might also offer the user the ability to vary the compression effect. Usually, the simplicity of using preset compression scaling of 1.0/1.0 for Standard, and a Maximum mode with preset compression scaling of 0.0/0.0 will be sufficient for most listeners who want to adjust dynamic range compression. It is noted that compression may be made scalable. Table 7.11. Examples of listening modes in a home theater system.
Late Night
minimum dynamic range
RF
Gain correction required –11dB
Standard
normal dynamic range
Line
none
Maximum
maximum dynamic range highest resolution through D/A for critical music material
Line
none +11dB dnmix dialnorm
Listening mode
DVD Audio direct
Description
Mode
Cstm 0
Compression scaling (high/low) 1.0/1.0 fixed 1.0/1.0 (or scalable) 0.0/0.0 0.0/0.0 (or scalable)
The “DVD audio direct” mode is shown in the table as an illustration of how Custom 0 mode might be used in special applications. However, this mode must be used with due caution. For example, one of the main reasons to use Custom 0 mode is so that dialog normalization is not applied in the digital domain, but possibly in the volume control instead. This means a few more decibels of low-level signal resolution can be extracted from the D/A converter. Yet whenever downmixing occurs, 11 dB of attenuation is automatically applied digitally, thus reducing resolution significantly in order to guarantee the downmixed signals will not overflow. Using Line mode prevents the loss of resolution because any peak signals that would potentially cause overload are dynamically limited when downmixing, thereby avoiding the forced attenuation. Assuming that any of the various gain corrections described above are handled in the electronic volume control section, they must not be visible to the user as a change to the volume control setting. The action must be completely transparent.
37 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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8.
Design considerations—stereo products
Stereo products—decoders with a maximum of two channels of audio output—include receivers of television, radio, cable, and satellite transmissions, or units that play back tapes, discs, or other types of prerecorded programs. These may be self-contained units with amplifiers and speakers, or they may be intended to serve as signal sources for other audio reproduction systems. Thus, the range of outputs from these products includes audible sound itself (from the speakers), power amplified outputs, line level signals, headphone jacks, and RF modulated carriers. They may also provide digital audio outputs in the form of conventional PCM, or they may deliver coded Dolby Digital signals either in digital form via S/PDIF, or in the proprietary RF channel as from laser disc players1. Each output type will need to meet appropriate levels of performance based on its purpose and user expectations. The features listed in Table 8.1 will serve to highlight the requirements (rqd), recommendations (rec), or designer options (opt) that relate to a given product. If the feature must not appear in a given product, it is marked “not applicable” (n/a). A blank means that the feature has to be chosen on the basis of format definition. Each of the features is described in more detail elsewhere in this section. The product types listed are: • • • • •
1-dec: 2-dec: 2-TV: LD: DVD:
1-channel Dolby Digital decoder or television 2-channel Dolby Digital control center or amplifier 2-channel Dolby Digital television laser disc player or other bitstream Source product 2-channel DVD, DTV, cable/satellite receiver, or tape player
1
The OVDA, Optical Video Disc Association, publishes “Guidelines for Laser Discs with Digital Data” defining the RF signal.
38 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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Table 8.1. Stereo product features.
2 2
Feature S/PDIF input S/PDIF output PCM S/PDIF output 48 kHz fs 44.1 kHz fs 32 kHz fs sub out w/LFE input signal status display Lt/Rt downmix capability Lo/Ro downmix dialog normalization full or scalable compression
8.1.
1-dec
2-dec rqd
2-TV opt
LD n/a
DVD opt*
opt
rqd
rqd
rqd*
rqd
n/a
opt
opt
opt
rec
rqd
opt
rqd n/a n/a n/a
rec
n/a
rqd rqd rqd rec
n/a
opt*
opt*
n/a
opt*
n/a
rqd
rqd
n/a
rqd
rqd
rec
rec
n/a
rec
rqd
rqd
rqd
n/a
rqd
rqd
rqd
rqd
n/a
rqd
Comments *if DVD is recordable. *RF Dolby Digital output may substitute for this
DTV, cable, LD std
*display range may not exceed decoding range other downmixes may be offered for use whenever a TV RF remodulator is provided may be deactivated only if resets to on with power-up may be switchable
Mode switches and indicators—stereo products
Information in the Dolby Digital bitstream makes it possible for the decoder to detect when surround signals are present using the “Lt/Rt” flag, so it is now possible to provide a surround indicator. This will help alert users to turn on their surround decoders. The Lt/Rt flag shall not force the decoder into the Pro Logic mode, nor shall the lack of the Lt/Rt flag prevent its use. The user decides when Pro Logic is used. The product may offer an automatic mode that uses the Lt/Rt flag to activate Pro Logic decoding when present.
8.2.
Specific considerations for 2-channel televisions
If the speakers or amplifier power have very limited capability, maximum compression should be left on full time. Refer to RF Mode description in Part 7. If the TV provides sufficient loudness capability to allow enjoyment of high dynamic range programs, the Line Out Mode should be used. Optionally, scalable compression may be offered to allow increased dynamics. Please review additional design information relevant to 2-channel TVs in Parts 4.1, 4.2, 4.3, 4.4, 6.1, 6.2, and 7.
39 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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9.
Design considerations—multichannel products
This section discusses the basic signal flow and mode switching features of A/V products.
9.1.
General product structures
Pro Logic decoders may be built to incorporate Dolby Digital decoding in the same unit, or may be designed to add Dolby Digital decoding by means of a module insert or separate outboard decoder. The general block diagram for a complete Pro Logic and Dolby Digital decoder follows. TAPE OUTPUT ANALOG AUDIO SELECTOR
DIGITAL AUDIO SELECTOR
2-CH A/D
IEC 1937 (S/PDIF) RECEIVER
DIGITAL, PRO LOGIC DECODE
BITSTREAM SELECTOR
CROSSOVER FILTERS
OUTPUT TIME DELAY
6-CH D/A
VOLUME, BALANCE CONTROLS
POWER AMPS
HEADPHONE OUTPUT
USER CONTROLS
SYSTEM CONTROLLER
Fig. 9.1. Dolby Digital decoder. Due to the presence of a digital Pro Logic processor and the S/PDIF input needed for Dolby Digital bitstreams, it becomes attractive to use these with PCM input signals via the same S/PDIF input circuit. If this is done, it is necessary to properly detect when these PCM signals have been pre-emphasized and to apply the appropriate de-emphasis so that they may be returned to the required flat audio response before further decoding takes place. Laser disc players with Dolby Digital capability may provide an RF output which requires a demodulator to recover the Dolby Digital bitstream. This demodulator can be an external device as shown in Fig. 9.2, or built into the A/V decoder as shown in Fig. 9.3.
AC-3 RF IN
IEC 1937 (S/PDIF) FORMATTER
AC-3 RF DEMOD
DIGITAL OUTPUT
OUTBOARD DEMODULATOR
Fig. 9.2. RF demodulator outboard decoder.
40 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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TAPE OUTPUT
AUDIO INPUTS
ANALOG AUDIO SELECTOR
PCM OR DIGITAL INPUT
DIGITAL AUDIO SELECTOR
AC-3 RF INPUT
2-CH A/D
IEC 1937 (S/PDIF) RECEIVER
BITSTREAM SELECTOR
DIGITAL, PRO LOGIC DECODE
AC-3 RF DEMOD
Fig. 9.3. A/V decoder with optional built-in RF demodulator. The features listed in Table 9.1 will serve to highlight the requirements (rqd), recommendations (rec), and optional (opt) features that relate to given Source (src) or Decoder (dec) products. If the feature must not appear in a given product, it is marked “not applicable” (n/a). Boxes left blank suggest the feature may not be relevant to that product. Each of the features is described in more detail in this section. The product types listed are: • • • • •
2-P/L: 3-3ST: 5-proc: 5-TV: 5-P/L:
2-channel Dolby Digital Source product with Dolby Surround Pro Logic decoder 2- or 3-channel Dolby Digital Source product with Dolby 3 Stereo decoder 5.1-channel Dolby Digital outboard decoder 5.1-channel Dolby Digital Source product (DTV, DVD, cable/satellite receiver) 5.1-channel Dolby Digital product with Pro Logic Surround decoder
41 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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Table 9.1. Multichannel product features. Feature
2-P/L src
2 2
S/PDIF input S/PDIF output 48 kHz fs content decodable 44.1 kHz fs content decodable 32 kHz fs content decodable 2-channel line inputs basic Dolby Surround Pro Logic Surround operation without surround speakers operation without center speaker noise seqncr Config 1 Config 2 Config 3 bass splitter master volume dialog normalization full or scalable compression
9.2.
3-3ST src
5-proc dec
5-TV src
5-P/L dec
Comments
rqd
rec
rqd
receive from all other Dolby Digital Sources
opt
opt
pass signals to all other Source products
rqd
rqd
rqd
rqd
rqd
rqd
rqd
DTV/DVD/LD std
opt
opt
rqd*
opt
rqd*
*rqd if IEC 1937 input provided
opt
opt
rqd*
opt
rqd*
*rqd if IEC 1937 input provided
rqd
rqd
opt
rqd
n/a
n/a
n/a
n/a
n/a
rqd
n/a
opt
rqd
rqd
n/a
rqd
rqd*
rec
rqd
*unless specifically waived
n/a
n/a
rqd*
rec
rqd
*unless specifically waived
rqd
rqd
rqd rqd rqd rqd*
rqd rqd rqd opt
rqd rqd rqd rqd*
rqd rqd (4-ch)
rqd rqd (3-ch)
n/a* (6-ch)
rqd (6-ch)
rqd (6-ch)
rqd
rqd
rqd
rqd
rqd
rqd
rqd
rqd
rqd
rqd
Fig. 9.6 Fig. 9.7 Fig. 9.8, *Grp A only *unless overrides main system master volume
may be switchable
Mode switches and indicators—multichannel products
A/V decoders with Dolby Digital will usually incorporate many more features than current Pro Logic units, making it important to design products with some basic commonality in the way they operate and the way they appear functionally. This does not mean every feature or mode must be included on every product. It only means that when such features do appear, they may
42 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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benefit from the use of standardized configurations and nomenclature to promote better consumer understanding and ease of operation, which is a primary goal.
9.3.
Listening mode selector
The sound that is reproduced by an audio/video system depends on what kinds of audio processing the decoder provides, and to an equal extent the capability of the program sources themselves. When listeners decide to reproduce programs with more than conventional stereo sound, there are two main choices to be made; creation or recreation. Creation regards adding new effects or synthesizing specific acoustic environments that are not part of the original program content, such as done in Theater, Stadium, or Hall modes. Recreation regards reproducing the full multichannel soundfield originally recorded in the program. The latter is the main objective behind Dolby multichannel audio technologies. For the first time, two different kinds of Dolby multichannel audio processing are available in the same licensed product, formally known as Dolby Surround Pro Logic and Dolby Digital. While only one will be used at a time, both use the same speakers and amplifiers, and deliver soundfields with the same basic intent. The key difference is that Dolby Digital is discrete and uses separate left and right surround channels, in contrast to the use of the adaptive matrix and mono surround channel found in Pro Logic. Typical A/V products will therefore provide various listening mode selector buttons (Stereo, Hall, Theater, etc.) alongside the now familiar Surround mode button.
Stereo Surround Theater
Stadium Hall
Stereo 2
Stadium Hall
2
O Digital O Pro Logic
O Digital O Pro Logic
Theater
2
The single Surround [ ] button allows the decoder to process sources automatically depending on their content: all analog and PCM sources are Pro Logic matrix processed, as are any 2-channel programs delivered by Dolby Digital. Multichannel and monophonic Dolby Digital programs are decoded and reproduced with no further matrix processing. In many cases, the user will know which decoding mode should be used, because it is directly tied with the specific input signal chosen. However, since Dolby Digital formats such as cable and DTV may mix the programs between 2-channel and 5.1-channel content depending on availability, the decoding mode may change between Dolby Digital and Pro Logic “on the fly” without any commands from the user. See Part 9.5 on source selector switching for more information.
43 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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To display which Dolby Surround decoding mode is in effect, Dolby Digital and Pro Logic indicators are necessary, but these may be located for optimum styling and utility, and need not be placed directly with the mode selector switch. An alternative switch marking arrangement that uses less space for the labels is shown below.
Stereo 2
O Digital O Pro Logic
Theater
Stadium Hall
Table 9.2 shows which Dolby Surround decoding mode is used and indicated for each type of program source. Notice that the 2/0 modes are delivered by Dolby Digital, but are indicated as Pro Logic since that is what determines the audible performance. Table. 9.2. Decoding mode vs. program content. Decode Mode Displayed “ Digital” “Pro Logic”
2
3/2
3/1
3/0
O
O
O
Program Content 2/1 2/0 Lt/Rt O O O
2/2
2/0 stereo
1/0
PCM/ analog
O O
O
9.3.1 Listening modes Two derivative modes of Dolby Surround are possible; 3 Stereo and Phantom center. Dolby 3 Stereo reproduces sound using only the 3 front channels. It is intended to be used either before surround speakers are installed, or for programs that might benefit from deriving a center channel output, but where the quality of the decoded surround output is unsatisfactory. Pro Logic decoders would normally apply logic steering to remove surround content from the left and right channels and steer it to the surround channel. In 3 Stereo that is prevented, so the surround content remains audible from the left and right channels. The surround speakers are muted. When Dolby Digital programs are received in the 3 Stereo mode, the surround information will be blended into the left and right front channels to achieve the same effect. An exception to this occurs with multichannel programs deliberately produced without a center channel, such as 2/2 and 2/1 formats. When programs with no center content are reproduced in the 3 Stereo mode, no center channel will be derived. The surround signals will still be downmixed into the front left and right channels. The Phantom mode redirects the center channel signal equally to the left and right channels, thus creating a conventional stereo effect, enhanced with a surround output. This mode is intended to be used either before a center speaker is installed, or for programs such as music performances where no picture is involved. While it is necessary for multichannel products to provide for operation in the 3 Stereo and Phantom modes, it is not necessary to offer direct user controls labeled 3 Stereo or Phantom on the front panel itself, as these modes can also be provided through the use of the speaker
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selection menu described in Part 9.9.1. A separate setup menu takes care of all speaker options, and this simplifies the daily use of the system by removing these extra listening mode choices from the main control areas. Products of higher complexity and sophistication may provide these listening modes for users who wish to deliberately reproduce multichannel programs either without a center speaker or without surround speakers for the reasons described above, even when all five main speakers are available in the system. In this case, the listening mode switches should be configured as follows:
Stereo 2
O Surround O 3 Stereo O Phantom
2
Theater Stadium Hall
O Digital O Pro Logic
2
The “ ” Dolby Surround button selects among Dolby Surround, Dolby 3 Stereo, and Phantom center modes in rotation. The “ ” button is referred to as the Dolby Surround button since that is how access to the various Dolby Surround modes is provided, even though it also gives access to the Dolby decoding mode that does not use the surround outputs; 3 Stereo. This will help keep the Dolby Surround mode nomenclature uniform for all Dolby Surround products. For on-screen displays, the “Dolby” should be used as follows.
Stereo Dolby O Digital O Pro Logic 3 Stereo Phantom Theater Stadium Hall The Stereo mode disables the logic matrix for 2-channel sources. With 4- and 5.1-channel Dolby Digital sources, the Dolby Digital processor will downmix to the Lo/Ro stereo compatible mode.
45 Copyright ©1995, 1997 Dolby Laboratories Licensing Corporation. All rights reserved. Dolby, AC-3, Pro Logic, and the double-D symbol are trademarks of Dolby Laboratories.
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Because the user is being given the ability to select 3 Stereo or Phantom reproduction in addition to conventional Stereo, sources will be reproduced or downmixed to those modes wherever possible, as shown in the Table 9.3: Table 9.3. Output signals resulting from various program content and listening modes. Delivered Program Content 3/2 3/1 3/0 2/2 2/1 2/0 Lt/Rt 2/0 stereo 1/0 PCM analog
Listening Mode Dolby Surround 3/2 3/1 3/0 2/2 2/1 3/1 M 3/1 M 1/0 3/1 M 3/1 M
3 Stereo
Phantom
3/0 3/0 3/0 2/0 2/0 3/0 M 3/0 M 1/0 3/0 M 3/0 M
2/2 2/1 2/0 2/2 2/1 2/1 M 2/1 M 2/0 * 2/1 M 2/1 M
Stereo 2/0 2/0 2/0 2/0 2/0 2/0 2/0 2/0 * 2/0 2/0
Notes: 1.
The numerical expression, 3/2, means 3 front channels and 2 surround channels are present in the main audio outputs, respectively.
2.
‘M’ designates that the adaptive matrix is used to derive the main outputs. If not designated, the outputs are derived directly or with fixed downmixing.
3.
‘*’ indicates dual mono.
4.
The 3 Stereo mode shall not produce a center output from 2/1 and 2/2 format programs.
The Stereo listening mode is the only one that creates signals compatible with conventional 2-channel audio and video recorders. This presents the possibility that the 2-channel downmixed Dolby Digital signals could be used for the tape outputs instead of the parallel 2-channel audio provided by the Source product, as done in all the other listening modes. However, this may not be advisable. See Part 9.6 for further information on the tape and headphone outputs.
9.4.
Products with additional signal processing
Additional signal processing may be provided in surround decoder products for various purposes. Some recreate the ambiance cues of real performance venues, such as concert halls or movie theaters. There may also be signal processing to enhance headphone listening to create a more spacious effect or to simulate the sense of a full surround system. Similar techniques may be used to enhance stereo reproduction modes or to recreate a surround sound effect from only the main left/right speakers.
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The surround modes listed above, Hall, Stadium, or Dolby, are used one at a time. There are other audio processing modes, however, that are designed to be used in conjunction with Dolby Surround decoding, usually where the effect of being in an actual movie theater is desired. Part of the attraction of experiencing movies in a well designed, full size theater comes from the acoustics and sense of scale of the theater itself. If this is the goal of the product, Dolby Surround decoding can serve as the starting point. These additional modes will typically be called “Theater” or “THX® Cinema,” and use digital signal processing (DSP) to simulate various acoustic qualities or sound reflections. Some processors have been programmed with the actual acoustic reflections measured in real theaters and may sound very convincing, while others are designed with more basic reverberation techniques. The THX Cinema mode is somewhat different from these in that it strives to emulate the soundfield characteristics of a large theater, but without the usual acoustic reverberations used by other DSP simulators. THX Home processors employ special equalization in the output channels and apply decorrelation processing for mono surround signals. Dolby Laboratories is allowing the use of its licensed Pro Logic and Dolby Digital technologies together with additional signal processing modes of the product, such as soundfield simulation. The following requirements apply: •
The Dolby Surround decoder section operates fully and without modification in name or function, including the surround time delay range, and is selected by user controls in the normal manner.
•
Any additional signal processing modes are selected by separate user controls having separate names, such as Theater, so that the user is fully aware that the additional mode operates independently of Pro Logic or Dolby Digital. Optionally, the same button used to select the Theater mode may automatically turn on the Dolby Surround mode, as long as it is clear that both modes are now operating together. The same policy applies to the THX processing mode.
The additional processing will usually be performed digitally. In first generation products, a second DSP IC will be cascaded to provide the needed processing capacity. This DSP can therefore also provide the equalization and crossover functions. See Fig. 9.4 below.
DIGITAL, PRO LOGIC DECODE
DSP EFFECTS OR EQUALIZERS
CROSSOVER FILTERS
OUTPUT TIME DELAY
6-CH D/A
VOLUME, BALANCE CONTROLS
Fig. 9.4. Surround decoder with added DSP processing.
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It is important to assure that any such additional signal processing not degrade the signal handling capabilities of the audio system such as by reducing the headroom before the volume control.
9.5.
Source selector switching
Audio/video program sources provide at least one, but often two or more types of signal output: Table 9.5. Output signals available from various sources. Consumer source
2-channel analog
cassette CD VCR Digital LD Digital set-top box DVD DVC
O O O O
2 2 2
2-channel PCM
RF television
2
5-channel analog
opt
opt
Digital RF n/a n/a n/a opt
opt O opt
2
Digital bitstream
opt
opt
O
O
opt
n/a
O O
opt opt
O O
O O
opt
n/a n/a
O
n/a
Digital 5.1-ch outboard
Source selector switches therefore need to handle a range of program sources, and also a choice of the specific signal output from that source. Only one output will be used at a time, so once the user has made a selection, the decoder should remember which output is preferred from a given source. For example, if a user prefers the direct PCM digital output from the CD be used instead of the analog outputs, even though both may be connected to the decoder, the PCM output will be heard each time the user selects the CD source. Once the CD is chosen, of course, the user may select the other output by means of a “digital/analog” selector switch. Products with Dolby Digital may follow the same method. A Dolby Digital capable laser disc player will have outputs for Dolby Digital (RF or S/PDIF), PCM, and analog. (The analog outputs on the player can select between the AFM left/right/stereo and the PCM soundtracks of the disc, but all outputs are analog at this point.) The Dolby Digital decoder’s LD input will select among analog, PCM, or Dolby Digital signals, as shown in Fig. 9.3. The decoder will remember which type of signal the user requested. If the decoder provides both the required S/PDIF input and the optional RF input with demodulator, the decoder should automatically select between them to select the Dolby Digital signal. If the decoder cannot automatically select between the RF and S/PDIF Dolby Digital inputs, this may be handled instead by means of a source setup menu. In either case, this will avoid the need to present the user with two kinds of Dolby Digital inputs during normal operation of the product, which must be avoided.
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9.6.
Tape and headphone outputs
The primary function of an A/V decoder is to process and control the available sources for reproduction over multiple loudspeakers. Related with this is the need to provide for headphone listening, and also for recording the selected sources for later playback. With the introduction of Dolby Digital, sources for the first time can deliver more channels of audio than can be used directly for headphones or conventional 2-channel recorders. This presents new challenges for the design of products that must handle source switching, recording, and decoding at the same time. It must be understood that tape and headphone outputs shall not be derived by summing the outputs of a Pro Logic decoder. 9.6.1 Headphone outputs Headphones are most often used as substitutes for speakers in order to provide private listening. Since it is also necessary to allow the volume to be adjusted, A/V decoder products typically provide a switch to mute the speakers when headphones are used. While Dolby Digital is capable of creating downmixes for various purposes, it can only derive one downmix at a time. When headphones are used, the decoder must be switched to a stereo mode so the entire audio program is made available via 2 channels. The easiest way to provide a headphone output, then, is to switch the speakers off and connect the headphones to the main left and right channels after the volume control. The user must turn off the surround modes (or simply select the Stereo mode) so conventional stereo sound is provided. This may also be done automatically when headphones are connected. 9.6.2 Tape outputs When monitoring multichannel sources over speakers, it is customary to provide a stereo version of the program for the tape outputs simultaneously. The preferred solution recognizes that Dolby Digital program Source products also have conventional stereo line outputs available in parallel to their IEC 1937 Dolby Digital bitstream outputs. For example, laser disc players will continue to provide stereo line outputs from the PCM tracks, and these will carry exactly the same audio program. Digital cable, DTV and DVD products will include internal 2-channel Dolby Digital decoders to provide stereo line outputs, even when Dolby Digital bitstream outputs are also provided. Please refer to Part 4.2 for descriptions of their operation. Therefore, while the A/V decoder is processing the Dolby Digital bitstream into a multichannel signal, it can be routing the source’s 2-channel analog signals to the tape outputs automatically as shown in Figs. 9.1 and 9.3. These analog signals will usually be Lt/Rt compatible mixes, and thus can be Pro Logic decoded at a later time. Part 9.3.1 describes how the stereo downmixed Dolby Digital signal may be used for the tape outputs instead of the existing stereo source tracks. There are 2 reasons not to do this, however. One is that this may complicate the audio switching somewhat, and will not lead to any specific benefit in the quality of the recording. Second, since the Source product will usually be downmixing to a compatible Lt/Rt signal (or using the existing one as from laser discs), the recordings being made will automatically be ready for Dolby Surround decoding. This leaves
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the option of downmixing to a different stereo version (not the Lt/Rt mix) which may be more effective for headphone or 2-channel speaker reproduction. Products that provide S/PDIF outputs for digital recording are not recommended to provide Dolby Digital output bitstreams. Dolby Digital bitstreams set the IEC 1397 ‘digital data’ flag, which tells the recorder that non-audio data is present. Consumer recorders cannot usually accept these signals. It may be preferable to deliver the decoded PCM to the S/PDIF output, but only if the complete audio program is present in the 2-channel output. It must not deliver, for example, only the left and right channels of a 5.1-channel soundtrack.
9.7.
Program format display
When programs adopted stereo for the first time, it became important to let consumers know which were stereo and which were mono. Pilot tones helped make this possible for broadcast formats, but printed labeling was needed for tapes and discs. Since Dolby Surround signals appear electrically the same as conventional stereo signals, there has not been any positive way to identify matrix encoded programs other than with written information or with identifying logos which may accompany them. The Dolby Digital bitstream’s BSI (bitstream information) provides explicit information on the audio format used. Because consumers will want to know what audio format is used for a given program—so that they can know what to expect regarding the spatial qualities of the soundtrack—a method of displaying this information has been developed. While it is highly recommended to include a program format display in any multichannel product, the decision rests with the product designers. If it is provided, however, the following basic layout concept should be used to promote uniformity and consumer familiarity. The recommended method for displaying this information is to provide (on the front panel or the on-screen display) an array of indicators roughly in a square to mimic the basic speaker layout. The “LFE” channel may also be included: L
C
R
LFE LS
S
RS
Fig. 9.5. Program format display. These will show which channels are used by the program, and examples of typical program formats are shown below. The “S” between the “LS” and “RS” lights indicates a mono surround channel is present, as in 3/1 mode. The “S” is also used when the Dolby Digital bitstream delivers a 2/0 program with the Lt/Rt flag set showing it has been Dolby Surround encoded, as shown in Fig. 9.6. This makes it possible to distinguish between conventional stereo and Dolby Surround encoded programs.
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mono
L
stereo
C
L
R
LFE LS
S
RS
LS
C
S
S
RS
5.1 surround
L
R
LFE LS
R
LFE
Dolby Surround
L
C
C
R
LFE RS
LS
S
RS
Fig. 9.6. Front panel indications of typical program formats. The range of the program format display must not exceed the range of audio outputs provided in the product. For example, a 2-channel product can at most provide a “stereo” indicator to show when programs are stereo, or a “surround” indicator to show when the outputs are surround encoded. It may not provide a full multichannel indicator as in Fig. 9.5, as this could imply the product includes multichannel audio outputs. Table 9.6 shows the indicators that might be found on stereo products with various source programs. Table. 9.6. Stereo product decoding mode vs. program format display. Decoder Downmix Mode Lo/Ro Lt/Rt
3/2
3/1
3/0
ST SUR
ST SUR
ST ST
Program Content 2/1 2/0 Lt/Rt ST ST SUR SUR SUR SUR 2/2
2/0 stereo ST ST
1/0
PCM/ analog ST ST
ST = Stereo SUR = Surround
9.7.1 LFE channel and display In contrast to the other main channels, the LFE channel delivers bass-only information (
