IEC 61937-3:2017

Digital audio - Interface for non-linear PCM encoded audio bitstreams applying IEC 60958 - Part 3: Non-linear PCM bitstreams according to the AC-3 and enhanced AC-3 formats

IEC 61937-3:2017 is available as IEC 61937-3:2017 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.
IEC 61937-3:2017 describes the method used to convey non-linear PCM bitstreams encoded according to the AC-3 and enhanced AC-3 formats. This third edition of IEC 61937-3 cancels and replaces the second edition published in 2007. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) removal of support for enhanced AC-3 bitstreams with a sampling frequency of 32 kHz;
b) updates to normative and informative references;
c) clarification of pause data-burst usage for enhanced AC-3 bitstreams.

General Information

• Status: Published
• Publication Date: 27-Jul-2017
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 33.160.30 - Audio systems
• Technical Committee: TA 20 - Analogue and digital audio
• Current Stage: PPUB - Publication issued
• Start Date: 28-Jul-2017
• Completion Date: 28-Jul-2017

Standards Content (sample)

IEC 61937-3
Edition 3.0 2017-07
INTERNATIONAL
STANDARD
Digital audio – Interface for non-linear PCM encoded audio bitstreams applying
IEC 60958 –
Part 3: Non-linear PCM bitstreams according to the AC-3 and enhanced
AC-3 formats
IEC 61937-3:2017-07(en)
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IEC 61937-3
Edition 3.0 2017-07
INTERNATIONAL
STANDARD
Digital audio – Interface for non-linear PCM encoded audio bitstreams applying
IEC 60958 –
Part 3: Non-linear PCM bitstreams according to the AC-3 and enhanced
AC-3 formats
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.160.30 ISBN 978-2-8322-4557-6

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
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– 2 – IEC 61937-3:2017 © IEC 2017
CONTENTS

FOREWORD ........................................................................................................................... 3

1 Scope .............................................................................................................................. 5

2 Normative references ...................................................................................................... 5

3 Terms, definitions and abbreviated terms ........................................................................ 5

3.7 Abbreviated terms ................................................................................................... 6

4 Mapping of the audio bitstream on to IEC 61937-1 .......................................................... 6

4.1 General ................................................................................................................... 6

4.2 AC-3 and enhanced AC-3 burst-info ........................................................................ 6

5 Format of AC-3 and enhanced AC-3 data-bursts .............................................................. 7

5.1 General ................................................................................................................... 7

5.2 Pause data-burst .................................................................................................... 7

5.3 Audio data-bursts .................................................................................................... 7

5.3.1 AC-3 data ........................................................................................................ 7

5.3.2 Latency of AC-3 decoding ................................................................................ 8

5.3.3 Enhanced AC-3 data ........................................................................................ 9

5.3.4 Latency of the enhanced AC-3 decoder ......................................................... 11

Bibliography .......................................................................................................................... 13

Figure 1 – AC-3 data-burst, with reference point R.................................................................. 7

Figure 2 – Latency of AC-3 decoding ...................................................................................... 8

Figure 3 – Enhanced AC-3 data-burst ................................................................................... 10

Figure 4 – Latency of enhanced AC-3 decoding .................................................................... 11

Table 1 – Fields of burst-info .................................................................................................. 6

Table 2 – Repetition period of the pause data-bursts .............................................................. 7

Table 3 – Data-type-dependent information when data-type bits 0-4 = 1 ................................ 8

Table 4 – Data-type-dependent information when data-type bits 0-4 = 21 and data-

type bits 5-6 = 0 .................................................................................................................... 10

Table 5 – Maximum enhanced AC-3 burst-payload size and bitstream data rate per

sampling frequency and IEC 60958 frame rate ...................................................................... 11

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IEC 61937-3:2017 © IEC 2017 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DIGITAL AUDIO –
INTERFACE FOR NON-LINEAR PCM ENCODED AUDIO BITSTREAMS
APPLYING IEC 60958 –
Part 3: Non-linear PCM bitstreams according to the AC-3 and
enhanced AC-3 formats
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

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International Standard IEC 61937-3 has been prepared by subcommittee technical area 4:

Digital system interfaces and protocols, of IEC technical committee 100: Audio, video and

multimedia systems and equipment.

This third edition of IEC 61937-3 cancels and replaces the second edition published in 2007.

This edition constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:

a) removal of support for enhanced AC-3 bitstreams with a sampling frequency of 32 kHz;

b) updates to normative and informative references;
c) clarification of pause data-burst usage for enhanced AC-3 bitstreams.
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– 4 – IEC 61937-3:2017 © IEC 2017
The text of this International Standard is based on the following documents:
CDV Report on voting
100/2720/CDV 100/2934/RVC

Full information on the voting for the approval of this International Standard can be found in

the report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts in the IEC 61973 series, published under the general title Digital audio –

Interface for non-linear PCM encoded audio bitstreams applying IEC 60958, can be found on

the IEC website.

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
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IEC 61937-3:2017 © IEC 2017 – 5 –
DIGITAL AUDIO –
INTERFACE FOR NON-LINEAR PCM ENCODED AUDIO BITSTREAMS
APPLYING IEC 60958 –
Part 3: Non-linear PCM bitstreams according to the AC-3 and
enhanced AC-3 formats
1 Scope

This part of IEC 61937 describes the method used to convey non-linear PCM bitstreams

encoded according to the AC-3 and enhanced AC-3 formats.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their

content constitutes requirements of this document. For dated references, only the edition

cited applies. For undated references, the latest edition of the referenced document (including

any amendments) applies.

IEC 61937-1:2007, Digital audio interface for non-linear PCM encoded audio bit streams

applying IEC 60958 – Part 1: General

IEC 61937-1:2007/AMD1:2011, Digital audio interface for non-linear PCM encoded audio bit

streams applying IEC 60958 – Part 1: General

IEC 61937-2, Digital audio interface for non-linear PCM encoded audio bit streams applying

IEC 60958 – Part 2: Burst-info
ETSI TS 102 366, Digital Audio Compression (AC-3, Enhanced AC-3) Standard
3 Terms, definitions and abbreviated terms
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
block identification flag

flag used to indicate that the first audio block of an enhanced AC-3 syncframe with a stream

type value of two formed the first audio block in the AC-3 syncframe from which it was

converted
3.2
converter synchronization flag

flag used for synchronization by a device that converts an enhanced AC-3 bitstream to a

bitstream compliant with an AC-3 decoder and indicates that the first block in this enhanced

AC-3 syncframe will form the first block of the AC-3 syncframe output by the conversion

process
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3.3
latency

delay time of an external audio decoder to decode an AC-3 or enhanced AC-3 data-burst,

defined as the sum of two values: the receiving delay time and the decoding delay time

3.4
stream type

parameter of an enhanced AC-3 syncframe identifying the type of substream of which the

syncframe is a part

Note 1 to entry: An enhanced AC-3 bitstream is constructed from one or more substreams, with each substream

being constructed from a sequence of syncframes.
3.5
substream identification

parameter of an enhanced AC-3 syncframe which, in conjunction with the stream type

parameter, identifies the substream in the bitstream of which the syncframe is a part

3.6
syncframe

minimum portion of the AC-3 or enhanced AC-3 audio serial bitstream capable of being fully

decoded, also known as a synchronization frame
3.7 Abbreviated terms
ATSC Advanced Television Systems Committee
ETSI European Telecommunications Standards Institute
4 Mapping of the audio bitstream on to IEC 61937-1
4.1 General
The coding of the bitstream and data-burst is in accordance with IEC 61937-1,

IEC 61937-1:2007/AMD1:2011 and IEC 61937-2, including field names such as "Pc", "Pa" and

"R".
4.2 AC-3 and enhanced AC-3 burst-info

The 16-bit burst-info contains information about the data that will be found in the data-burst

(see Table 1).
Table 1 – Fields of burst-info

Bits of Data-type Data-type Contents Reference Repetition period of data-burst measured in

Pc bits 0-4 bits 5-6 point R
IEC 60958 frames
0 to 6 1 0 AC-3 R-AC-3 1 536
1 to 3 Reserved
2 to 20 According to IEC 61937
21 0 Enhanced AC-3 Bit 0 of Pa 6 144
1 to 3 According to IEC 61937
22 to 31 According to IEC 61937
7 to 15 According to IEC 61937
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IEC 61937-3:2017 © IEC 2017 – 7 –
5 Format of AC-3 and enhanced AC-3 data-bursts
5.1 General

This clause specifies the audio data-bursts AC-3 and enhanced AC-3. Specific properties

such as reference points, repetition periods, the method of filling stream gaps and decoding

latency are specified.

The decoding latency (or delay), indicated for the data-type bits 0-4, should be used by the

transmitter to schedule data-bursts as necessary to establish synchronization between picture

and decoded audio.
5.2 Pause data-burst
Pause data-bursts for AC-3 and enhanced AC-3 are given in Table 2.
Table 2 – Repetition period of the pause data-bursts
Data-type bits 0-4 of audio data-burst Repetition period of pause data-burst
Mandatory Recommended
AC-3 - 3 IEC 60958 frames
Enhanced AC-3 - 4 IEC 60958 frames
5.3 Audio data-bursts
5.3.1 AC-3 data

The AC-3 bitstream consists of a sequence of AC-3 syncframes. The data-type bits 0-4 of an

AC 3 data-burst is 1. An AC-3 syncframe represents 1 536 samples of each encoded audio

channel (left, centre, etc.). The data-burst is headed with a burst-preamble followed by the

burst-payload. The burst-payload of each data-burst of AC-3 data shall c
...