ISO/IEC 13818-3:1998

INTERNATIONAL ISO/IEC
STANDARD 13818-3
Second edition
1998-04-15
Information technology — Generic coding
of moving pictures and associated audio
information —
Part 3:
Audio
Technologies de l'information — Codage générique des images animées
et des informations sonores associées —
Partie 3: Son
Reference number
B C
Contents
Page
Section 1: General. 1
1.1 Scope. 1
1.2 Normative references. 1
Section 2: 2
Technical elements .
2.1 2
Definitions.
2.2 Symbols and abbreviations. 13
2.3 Method of describing bit stream syntax. 16
2.4 Requirements for Extension of ISO/IEC 11172-3 to Lower Sampling Frequencies. 18
2.5 Requirements for Extension of ISO/IEC 11172-3 to Multichannel Audio . 24
2.6 Registration of Copyright Identifiers. 65
Annexes
A. 66
Diagrams.
B. 69
Tables .
C. The encoding process . 73
D. Psychoacoustic models . 84
E. Ancillary Data Use. 108
F. List of patent holders. 110
G. Registration Procedure . 112
H. Registration Application Form . 114
I. Registration Authority. 115
© ISO/IEC 1998
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by
any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the
publisher.
ISO/IEC Copyright Office • Case Postale 56 • CH1211 Genève 20 • Switzerland
Printed in Switzerland.
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© ISO/IEC ISO/IEC 13818-3:1998(E)
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are members of
ISO or IEC participate in the development of International Standards through technical committees established
by the respective organization to deal with particular fields of technical activity. ISO and IEC technical
committees collaborate in fields of mutual interest. Other international organizations, governmental and non-
governmental, in liaison with ISO and IEC, also take part in the work.
In the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC
JTC 1. Draft International Standards adopted by the joint technical committee are circulated to national bodies
for voting. Publication as an International Standard requires approval by at least 75 % of the national bodies
casting a vote.
International Standard ISO/IEC 13818-3 was prepared by Joint Technical Committee ISO/IEC JTC 1,
Information technology, Subcommittee SC 29, Coding of audio, picture, multimedia and hypermedia
information.
This second edition cancels and replaces the first edition (ISO/IEC 13818-3:1995), which has been technically
revised.
ISO/IEC 13818 consists of the following parts, under the general title Information technology — Generic coding
of moving pictures and associated audio information:
– Part 1: Systems
– Part 2: Video
– Part 3: Audio
– Part 4: Compliance testing
– Part 5: Software simulation
– Part 6: Extensions for DSM-CC
– Part 7: Advanced Audio Coding (AAC)
– Part 9: Extension for real time interface for systems decoders
– Part 10: Conformance extensions for DSM-CC
Annexes A and B form an integral part of this part of ISO/IEC 13818. Annexes C to I are for information only.
iii
Introduction
ISO/IEC 13818 was prepared by SC29/WG11, also known as MPEG (Moving Pictures Expert Group). MPEG
was formed in 1988 to establish a standard for the coded representation of moving pictures and associated audio
stored on digital storage media.
ISO/IEC 13818 is published in three parts. Part 1 - systems - specifies the system coding layer of the standard. It
defines a multiplexed structure for combining audio and video data and means of representing the timing
information needed to replay synchronised sequences in real-time. Part 2 - video - specifies the coded
representation of video data and the decoding process required to reconstruct pictures. Part 3 - audio - specifies
the coded representation of audio data and the decoding process required to decode audio signals.
The technical changes in this 2nd edition compared to the first publication of ISO/IEC 13818-3 (1995) are:
1. In the first publication, certain combinations of dynamic crosstalk and prediction were not prohibited but not
practically implementable. In this 2nd revision, these combinations are explicitly prohibited.
2. In the first publication, a low-pass filter was to be applied to the monophonic surround signal in matrix
mode 2 (analogue surround mode). This filter is omitted in this edition, greatly simplifying the decoder.
3. The description of the syntax of the LFE channel was ambiguous. This description has been clarified.
Next to these technical changes, many editorial changes have been made, improving readability and clarity.
0.1 Extension of ISO/IEC 11172-3 Audio Coding to Lower Sampling Frequencies
In order to achieve better audio quality at very low bit rates (<64 kbit/s per audio channel), in particular if
compared with ITU-T (formerly CCITT) Recommendation G.722 performance, three additional sampling
frequencies are provided for ISO/IEC 11172-3 layers I, II and III. The additional sampling frequencies (Fs) are
16 kHz, 22,05 kHz and 24 kHz. This allows corresponding audio bandwidths of approximately 7,5 kHz,
10,3 kHz and 11,25 kHz. The syntax, semantics, and coding techniques of ISO/IEC 11172-3 are maintained
except for a new definition of the sampling frequency field, the bitrate index field, and the bit allocation tables.
These new definitions are valid if the ID bit in the ISO/IEC 11172-3 header equals zero. To obtain the best audio
performance, the parameters of the psychoacoustic model used in the encoder have to be changed accordingly.
With these sampling frequencies, the duration of the audio frame corresponds to:
Layer Sampling Frequency in kHz
16 22,05 24
I 24 ms 17,41. ms 16 ms
II 72 ms 52,24. ms 48 ms
III 36 ms 26,12. ms 24 ms
0.2 Low bitrate coding of multichannel audio
0.2.1 Universal multichannel audio system
A standard on low bit rate coding for mono or stereo audio signals was established by MPEG-1 Audio in
ISO/IEC 11172-3. This standard is applicable for carrying of high quality digital audio signals associated with or
without picture information on storage media or transmission channels with limited capacity.
The ISO/IEC 11172-3 audio coding standard can be used together with both MPEG-1 and MPEG-2 Video as
long as only two-channel stereo is required. MPEG-2 Audio (ISO/IEC 13818-3) provides the extension up to 3/2
multichannel audio and an optional low frequency enhancement channel (LFE).
This part of ISO/IEC 13818 describes an audio subband coding system called ISO/MPEG-Audio Multichannel,
which can be used to transfer high quality digital multichannel and/or multilingual audio information on storage
media or transmission channels with limited capacity. One of the basic features is the backwards compatibility to
ISO/IEC 11172-3 coded mono, stereo or dual channel audio programmes. It is designed for use in different
applications as considered by the ISO/MPEG audio group and the specialist groups TG 10/1, 10/2 and 10/3 of
the ITU-R (previously CCIR).
Multichannel audio systems provide enhanced stereo performance compared to conventional two channel audio
systems. It is recognised that improved presentation performance is desirable not only for applications with
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© ISO/IEC ISO/IEC 13818-3:1998(E)
accompanying picture but also for audio-only applications. A universal and compatible multichannel audio
system applicable to satellite or terrestrial television broadcasting, digital audio broadcasting (terrestrial and
satellite), as well as other non-broadcasting media, e.g.,
CATV Cable TV Distribution
CDAD Cable Digital Audio Distribution
DAB Digital Audio Broadcast
DVD Digital Versatile Disc
ENG Electronic News Gathering (including Satellite News Gathering)
HDTV High Definition Television
IPC Interpersonal Communications (video conference, videophone, etc.)
ISM Interactive Storage Media (optical disks, etc.)
NDB Network Database Services (via ATM, etc.)
DSM Digital Storage Media (digital VTR, etc.)
EC Electronic Cinema
HTT Home Television Theatre
ISDN Integrated Services Digital Network
seems to be very attractive to the manufacturer, producer and consumer.
0.2.2 Representation of multichannel audio
0.2.2.1 The 3/2-stereo plus LFE format
Regarding stereophonic presentation, specialist groups of ITU-R, SMPTE, and EBU recommend the use of an
additional centre loudspeaker channel C and two surround loudspeaker channels LS and RS, augmenting the
front left and right loudspeaker channels L and R. This reference audio format is referred to as "3/2-stereo"
(3 front / 2 surround loudspeaker channels) and requires the transmission of five appropriately formatted audio
signals.
For audio accompanying picture applications (e.g. HDTV), the three front loudspeaker channels ensure sufficient
directional stability and clarity of the picture related frontal images, according to the common practice in the
cinema. The dominant benefit is the "stable centre", which is guaranteed at any location of the listener and
important for most of the dialogue.
Additionally, for audio-only applications, the 3/2-stereo format has been found to be an improvement over two-
channel stereophony. The addition of one pair of surround loudspeaker channels allows improved realism of
auditory ambience.
A low frequency enhancement channel (in this part of ISO/IEC 13818 called LFE channel) can, optionally, be
added to any of these configurations. The purpose of this channel is to enable listeners to extend the low
frequency content of the reproduced programme in terms of both frequency and level. In this way it is the same as
the LFE channel proposed by the film industry for their digital sound systems.
The LFE channel should not be used for the entire low frequency content of the multichannel sound presentation.
The LFE channel is optional at the receiver, and thus should only carry low frequency sound effects, which may
have a high level. The LFE channel is not included in any dematrixing operation in the decoder. The sampling
frequency of the LFE channel corresponds to the sampling frequency of the main channels, divided by a factor of
96. This provides 12 LFE samples within one audio frame. The LFE channel is capable of handling signals in the
range from 15 Hz to 120 Hz.
0.2.2.2 Compatibility
Extension from 2/0-stereo towards multichannel sound.
As a result of the widespread use of conventional two-channel stereo (2/0-stereo) reproduction, compatibility
with existing 2/0-stereo sound reproduction systems or with existing matrixed surround sound receivers has to be
maintained. This means that for many applications a basic stereo signal which contains an appropriate downmix
of the audio information of the multichannel programme has to be transmitted together with the multichannel
audio information. Appropriate downmix equations are given by equation pairs (1,2), (3,4), (5,6) and (7,8).
v
Lo = L + ½√2 C + ½√2 LS (1)
* *
Ro = R + ½√2 C + ½√2 RS (2)
* *
or
Lo = L + ½√2 C + ½ LS (3)
* *
Ro = R + ½√2 C + ½ RS (4)
* *
or
Lo = L (5)
Ro = R (6)
or
Lo = L + ½√2 C − ½√2 jS (7)
* *
Ro = R + ½√2 C + ½√2 jS (8)
* *
where jS is derived from LS and RS by calculation of the mono component. Then, a dynamic range compression
and 90 degrees phase shift are applied to this component. The downmix (7,8) is suitable for existing matrixed
surround decoders.
The format of an ISO/IEC 13818-3 bit stream is such that an ISO/IEC 11172-3 audio decoder properly decodes
the basic stereo information according to one of the sets of downmix equations above (see 0.2.3.1). Compatibility
with existing surround sound decoders by use of equations (7) and (8) has not been verified at the time of printing
of this part of ISO/IEC 13818.
In the case of this part of ISO/IEC 13818, three different possibilities can be identified to provide to the user a
basic stereo downmix together with the multichannel audio information:
1. Transmitting the 2/0-stereo sound inherently with the multichannel information in one bit stream in a
backwards compatible way with ISO/
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