Digital audio interface - Part 1: General

IEC 60958-1:2021 is available as IEC 60958-1:2021 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.
IEC 60958-1:2021 describes a serial, uni-directional, self-clocking interface for the interconnection of digital audio equipment for consumer and professional applications. It provides the basic structure of the interface. Separate documents define items specific to particular applications. The interface is primarily intended to carry monophonic or stereophonic programmes, encoded using linear PCM and with a resolution of up to 24 bits per sample. When used for other purposes, the interface is able to carry audio data coded other than as linear PCM coded audio samples. Provision is also made to allow the interface to carry data related to computer software, multimedia technologies, or signals coded using non linear PCM. The format specification for these applications is not part of this document. The interface is intended for operation at audio sampling frequencies of 32 kHz and above. Auxiliary information is transmitted along with the programme. IEC 60958-1:2021c ancels and replaces the third edition published in 2008, and Amendment 1:2014. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
a) The relevant part of IEC 60958-5 is supported.

Interface audionumérique - Partie 1: Généralités

IEC 60958-1:2021 est disponible sous forme de IEC 60958-1:2021 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.
L'IEC 60958-1:2021 décrit une interface série unidirectionnelle et autosynchronisante pour l'interconnexion des appareils audionumériques destinés aux applications grand public et professionnelles.
Elle fournit la structure de base de l'interface. Les points spécifiques à des applications particulières sont définis dans des documents distincts.
Cette interface est essentiellement destinée à acheminer des programmes monophoniques ou stéréophoniques, qui utilisent un codage MIC linéaire et une résolution jusqu'à 24 bits par échantillon.
Lorsqu'elle est utilisée à d'autres fins, cette interface est capable d'acheminer des données audio codées autres que des échantillons audio à codage MIC linéaire. Des dispositions ont également été prises pour permettre à l'interface d'acheminer des données relatives à des logiciels, des technologies multimédias ou des signaux à codage MIC non linéaire. La spécification du format de ces applications ne relève pas du présent document.
L'interface est destinée à fonctionner à des fréquences d'échantillonnage audio supérieures ou égales à 32 kHz. Des informations auxiliaires sont transmises avec le programme.
L'IEC 60958-1:2021 annule et remplace la troisième édition parue en 2008, et l'Amendement 1:2014. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) la partie pertinente de l'IEC 60958-5 est prise en compte.

General Information

Status
Published
Publication Date
31-Aug-2021
Current Stage
PPUB - Publication issued
Completion Date
01-Sep-2021
Ref Project

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IEC 60958-1
Edition 4.0 2021-09
INTERNATIONAL
STANDARD
Digital audio interface –
Part 1: General
IEC 60958-1:2021-09(en)
---------------------- Page: 1 ----------------------
THIS PUBLICATION IS COPYRIGHT PROTECTED
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---------------------- Page: 2 ----------------------
IEC 60958-1
Edition 4.0 2021-09
INTERNATIONAL
STANDARD
Digital audio interface –
Part 1: General
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.160.01 ISBN 978-2-8322-1017-0

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

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC 60958-1:2021 © IEC 2021
CONTENTS

FOREWORD ......................................................................................................................... 4

1 Scope ............................................................................................................................ 6

2 Normative references..................................................................................................... 6

3 Terms and definitions .................................................................................................... 6

4 Interface format ............................................................................................................. 8

4.1 Structure of format ................................................................................................ 8

4.1.1 Sub-frame format ........................................................................................... 8

4.1.2 Frame format ................................................................................................. 9

4.2 Channel coding ................................................................................................... 10

4.3 Preambles .......................................................................................................... 10

4.4 Validity bit ........................................................................................................... 11

5 Channel status ............................................................................................................ 11

5.1 General ............................................................................................................... 11

5.2 Applications ........................................................................................................ 11

5.3 General assignment of the first and second channel status bits ............................ 11

5.4 Category code ..................................................................................................... 12

6 User data .................................................................................................................... 14

6.1 General ............................................................................................................... 14

6.2 Applications ........................................................................................................ 14

6.2.1 Professional use .......................................................................................... 14

6.2.2 Consumer use .............................................................................................. 14

7 Electrical requirement .................................................................................................. 14

7.1 Consumer application .......................................................................................... 14

7.1.1 General ....................................................................................................... 14

7.1.2 Timing accuracy ........................................................................................... 14

7.1.3 Unbalanced line ........................................................................................... 15

7.2 Professional application ...................................................................................... 18

8 Optical requirements .................................................................................................... 18

8.1 Consumer application .......................................................................................... 18

8.1.1 Configuration of optical connection ............................................................... 18

8.1.2 Optical connector ......................................................................................... 18

8.2 Professional applications ..................................................................................... 19

Annex A (informative) The use of the validity bit ................................................................. 20

Annex B (informative) Application documents and specifications ......................................... 21

Annex C (informative) A relationship of the IEC 60958 series families ................................. 22

Annex D (informative) Transmission of CD data other than linear PCM audio ...................... 24

Annex E (informative) The IEC 60958 series conformant data format .................................. 25

Annex F (informative) Stream change ................................................................................. 26

Annex G (informative) Characteristics of optical connection ................................................ 28

Bibliography ....................................................................................................................... 30

Figure 1 – Sub-frame format (linear PCM application) ............................................................ 9

Figure 2 – Frame format ....................................................................................................... 9

Figure 3 – Channel coding .................................................................................................. 10

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IEC 60958-1:2021 © IEC 2021 – 3 –

Figure 4 – Preamble M (shown as 11100010) ...................................................................... 11

Figure 5 – Simplified example of the configuration of the circuit (unbalanced) ...................... 15

Figure 6 – Rise and fall times .............................................................................................. 16

Figure 7 – Intrinsic jitter measurement filter ......................................................................... 16

Figure 8 – Eye diagram ....................................................................................................... 17

Figure 9 – Receiver jitter tolerance template ........................................................................ 17

Figure 10 – Basic optical connection ................................................................................... 18

Figure C.1 – Relationships of the IEC 60958 families ........................................................... 22

Figure F.1 – Audio sources and AV receiver model .............................................................. 26

Figure F.2 – Switching from linear PCM to non linear PCM .................................................. 26

Figure F.3 – Switching from non linear PCM to linear PCM .................................................. 27

Figure F.4 – Switching from non-linear PCM to non-linear PCM ........................................... 27

Table 1 – Preamble coding ................................................................................................. 10

Table 2 – Channel status data format .................................................................................. 13

Table B.1 – Application documents and specifications ......................................................... 21

Table C.1 – data_type values and application ...................................................................... 23

Table G.1 – Characteristics of standard optical connection (optical interface) ....................... 28

Table G.2 – Characteristics of optical transmitter (optical interface) ..................................... 28

Table G.3 – Characteristics of optical receiver (optical interface) ......................................... 29

Table G.4 – Characteristics of fibre optic cable .................................................................... 29

Table G.5 – Optical power budget for the link with plastic fibre ............................................. 29

---------------------- Page: 5 ----------------------
– 4 – IEC 60958-1:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DIGITAL AUDIO INTERFACE –
Part 1: General
FOREWORD

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

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international

co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and

in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,

Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their

preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with

may participate in this preparatory work. International, governmental and non-governmental organizations liaising

with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for

Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence between

any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent

rights. IEC shall not be held responsible for identifying any or all such patent rights.

IEC 60958-1 has been prepared by technical area 20: Analogue and digital audio, of IEC

technical committee 100: Audio, video and multimedia systems and equipment. It is an

International Standard.

This fourth edition cancels and replaces the third edition published in 2008, and

Amendment 1:2014. This edition constitutes a technical revision.

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

edition:
a) The relevant part of IEC 60958-5 is supported.
---------------------- Page: 6 ----------------------
IEC 60958-1:2021 © IEC 2021 – 5 –
The text of this International Standard is based on the following documents:
Draft Report on voting
100/3544/CDV 100/3593/RVC

Full information on the voting for its approval can be found in the report on voting indicated in

the above table.
The language used for the development of this International Standard is English.

A list of all parts of the IEC 60958 series, under the general title Digital audio interface, can be

found on the IEC website.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in

accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available

at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are

described in greater detail at www.iec.ch/standardsdev/publications.

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

stability date indicated on the IEC website under 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.
---------------------- Page: 7 ----------------------
– 6 – IEC 60958-1:2021 © IEC 2021
DIGITAL AUDIO INTERFACE –
Part 1: General
1 Scope

This part of IEC 60958 describes a serial, uni-directional, self-clocking interface for the

interconnection of digital audio equipment for consumer and professional applications.

It provides the basic structure of the interface. Separate documents define items specific to

particular applications.

The interface is primarily intended to carry monophonic or stereophonic programmes, encoded

using linear PCM and with a resolution of up to 24 bits per sample.

When used for other purposes, the interface is able to carry audio data coded other than as

linear PCM coded audio samples. Provision is also made to allow the interface to carry data

related to computer software, multimedia technologies, or signals coded using non-linear PCM.

The format specification for these applications is not part of this document.

The interface is intended for operation at audio sampling frequencies of 32 kHz and above.

Auxiliary information is transmitted along with the programme.
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 60268-11:1987, Sound system equipment – Part 11: Application of connectors for the

interconnection of sound system components
IEC 60958-3, Digital audio interface – Part 3: Consumer applications

IEC 60958-4 (all parts), Digital audio interface – Part 4: Professional applications

IEC 60958-5, Digital audio interface – Part 5: Consumer application enhancement
3 Terms and definitions
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
sampling frequency
frequency of the samples representing an audio signal
---------------------- Page: 8 ----------------------
IEC 60958-1:2021 © IEC 2021 – 7 –

Note 1 to entry: When more than one signal is transmitted through the same interface, the sampling frequencies

are identical.
3.2
audio sample word

value of a digital audio sample; representation is linear in 2's complement binary form

Note 1 to entry: Positive numbers correspond to positive analogue voltages at the input of the analogue-to-digital

converter (ADC).
3.3
auxiliary sample bit

four least significant bits (LSBs) which can be assigned as auxiliary sample bits and used for

auxiliary information when the number of audio sample bits in the main data field is less than

or equal to 20
3.4
validity bit

bit indicating whether the main data field bits in the sub-frame (time slots 4 to 27 or 8 to 27,

depending on the audio word length as described in 4.1.1) are reliable or not
3.5
channel status

data carrying, in a fixed format, information associated with each main data field channel which

is decodable by any interface user

Note 1 to entry: Examples of information to be carried in the channel status are: length of audio sample words, pre-

emphasis, sampling frequency, time codes, alphanumeric source and destination codes.

3.6
user data
data provided to carry any other information
3.7
parity bit

bit provided to permit the detection of an odd number of errors resulting from malfunctions in

the interface
3.8
preamble
specific patterns used for synchronization
Note 1 to entry: There are three different preambles (see 4.3).
3.9
sub-frame
fixed structure used to carry information (see 4.1.1 and 4.1.2)
3.10
frame
sequence of two successive and associated sub-frames
3.11
block
group of 192 consecutive frames

Note 1 to entry: The start of a block is designated by a special sub-frame preamble (see 4.3).

3.12
channel coding

coding method by which the binary digits are represented for transmission through the interface

---------------------- Page: 9 ----------------------
– 8 – IEC 60958-1:2021 © IEC 2021
3.13
unit interval (UI)
shortest nominal time interval in the coding scheme
Note 1 to entry: There are 128 UI in a sample frame.
3.14
interface jitter

deviation in the timing of interface data transitions (zero crossings) when compared with an

ideal clock
3.15
intrinsic jitter

output interface jitter of a device that is either free-running or is synchronized to a jitter-free

reference
3.16
jitter gain

ratio of the amplitude of jitter components at the output to their amplitude at the synchronization

input to the device under test
4 Interface format
4.1 Structure of format
4.1.1 Sub-frame format

Each sub-frame is divided into 32 time slots, numbered from 0 to 31 (see Figure 1).

Time slots 0 to 3 (preambles) carry one of the three permitted preambles (see 4.1.2 and 4.3;

also see Figure 2).

Time slots 4 to 27 (main data field) carry the audio sample word in linear 2's complement

representation. The most significant bit (MSB) is carried by time slot 27.
When a 24-bit coding range is used, the LSB is in time slot 4 (see Figure 1).

When a 20-bit coding range is used, time slots 8 to 27 carry the audio sample word with the LSB

in time slot 8. Time slots 4 to 7 may be used for other applications. Under these circumstances,

the bits in the time slots 4 to 7 are designated auxiliary sample bits (see Figure 1).

If the source provides fewer bits than the interface allows (either 20 or 24), the unused LSBs

are set to a logical "0".

For a non-linear PCM audio application or a data application the main data field may carry any

other information.

Time slot 28 (validity bit) carries the validity bit associated with the main data field (see 4.4).

Time slot 29 (user data bit) carries 1 bit of the user data channel associated with the main data

field channel transmitted in the same sub-frame. For the applications, refer to the other parts

of IEC 60958.

Time slot 30 (channel status bit) carries 1 bit of the channel status information associated with

the main data field channel transmitted in the same sub-frame. For details refer to the other

parts of IEC 60958.
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IEC 60958-1:2021 © IEC 2021 – 9 –

Time slot 31 (parity bit) carries a parity bit such that time slots 4 to 31 inclusive carry an even

number of ones and an even number of zeroes (even parity).
NOTE The preambles have even parity as an explicit property.
Figure 1 – Sub-frame format (linear PCM application)

Annex E describes the IEC 60958 series conformant data format that utilises the sub-frame

format.
4.1.2 Frame format

A frame is uniquely composed of two sub-frames (see Figure 2). For linear coded audio

applications, the rate of transmission of frames normally corresponds exactly to the source

sampling frequency.

In 2-channel operation mode, the samples taken from both channels are transmitted by time

multiplexing in consecutive sub-frames. The first sub-frame (left or "A" channel in stereophonic

operation and primary channel in monophonic operation) normally starts with preamble "M".

However, the preamble changes to preamble "B" once every 192 frames to identify the start of

the block structure used to organize the channel status information. The second sub-frame

(right or "B" channel in stereophonic operation and secondary channel in monophonic operation)

always starts with preamble "W".

In single channel operation mode in a professional application, the frame format is the same as

in the 2-channel mode. Data is carried in the first sub-frame and may be duplicated in the

second sub-frame. If the second sub-frame is not carrying duplicate data, then time slot 28,

(validity flag) shall be set to logical "1".

NOTE For historical reasons preambles "B", "M" and "W" are, for use in professional applications, referred to as

"Z", "X" and "Y", respectively.

Annex C describes the relation of the IEC 60958 series families based on the frame format.

Figure 2 – Frame format
---------------------- Page: 11 ----------------------
– 10 – IEC 60958-1:2021 © IEC 2021
4.2 Channel coding

To minimize the direct current (d.c.) component on the transmission line, to facilitate clock

recovery from the data stream and to make the interface insensitive to the polarity of

connections, time slots 4 to 31 are encoded in biphase-mark.

Each bit to be transmitted is represented by a symbol comprising two consecutive binary states.

The first state of a symbol is always different from the second state of the previous symbol. The

second state of the symbol is identical to the first if the bit to be transmitted is logical "0".

However, it is different if the bit is logical "1" (see Figure 3).
Figure 3 – Channel coding
4.3 Preambles

Preambles are specific patterns providing synchronization and identification of the sub-frames

and blocks.

To achieve synchronization within one sampling period and to make this process completely

reliable, these patterns violate the biphase-mark code rules, thereby avoiding the possibility of

data imitating the preambles.

A set of three preambles is used. These preambles are transmitted in the time allocated to four

time slots at the start of each sub-frame (time slots 0 to 3), and are represented by eight

successive states. The first state of the preamble is always different from the second state of

the previous symbol (representing the parity bit). Depending on this state, the preambles are

as shown in Table 1.
Table 1 – Preamble coding
Preceding state 0 1
Preamble code Channel coding
"B" or "Z" 11101000 00010111 Sub-frame 1 and
(see note to 4.1.2) the start of the block
"M" or "X" 11100010 00011101 Sub-frame 1
"W" or "Y" 11100100 00011011 Sub-frame 2

Like biphase code, these preambles are d.c. free and provide clock recovery. They differ in at

least two states from any valid biphase sequence.
Figure 4 represents preamble "M".

NOTE Owing to the even-parity bit in time slot 31, all preambles start with a transition in the same direction

(see 4.1.1). Thus, only one of these sets of preambles is, in practice, transmitted through the interface. However, it

is necessary for both sets to be decodable because either polarity is possible in a connection.

---------------------- Page: 12 ----------------------
IEC 60958-1:2021 © IEC 2021 – 11 –
Figure 4 – Preamble M (shown as 11100010)
4.4 Validity bit

The validity bit is logical "0" if the information in the main data field is reliable, and it is logical

"1" if it is not. There is no default state for the validity bit.

NOTE For transmissions not using a linear PCM coding, this bit can be set. This is intended to prevent accidental

decoding of non-audio data to analogue before a complete channel status block is received. See Annex A.

5 Channel status
5.1 General

For every sub-frame, the channel status provides information related to the data carried in the

main data field of that same sub-frame.

Channel status information is organised in a 192-bit block, subdivided into 24 bytes. The first

bit of each block is carried in the frame with preamble "B". The channel status data format is

defined in Table 2.

The specific organisation depends on the application. In the descriptions, the suffix "0"

designates the first byte or bit. Where channel status bits are combined to form non-binary

values, the least significant bit should be transmitted first, unless otherwise indicated.

5.2 Applications

The primary application is indicated by the first channel status bit (bit 0) of a block as defined

in 5.3.
For professional applications, refer to IEC 60958-4.
For consumer applications, refer to IEC 60958-3 and IEC 60958-5.

Secondary applications may be defined within the framework of these primary applications.

Application documents or specifications are listed in Annex B.
5.3 General assignment of the first and second channel status bits

The first and second channel status bits (bit 0 and bit 1) are specified as follows.

Byte 0
Bit 0 "0" Consumer use of channel status block.
---------------------- Page: 13 ----------------------
– 12 – IEC 60958-1:2021 © IEC 2021
"1" Professional use of channel status block.
Bit 1 "0" Main data field represents linear PCM samples.
"1" Main data field used for other purposes.

Annex D describes an exception case of bit 1 status. Annex F describes a receiver's behaviour

when bit 1 is being altered.
5.4 Category code

Channel status including category code is defined in IEC 60958-3 for consumer applications;

these category codes are used for other variations of IEC 60958 for consumer use, such as

IEC 61937.

Also, channel status is defined in IEC 60958-4 for professional applications; these channel

statuses are used for other variations for professional use such as SMPTE ST 337 and others.

---------------------- Page: 14 ----------------------
IEC 60958-1:2021 © IEC 2021 – 13 –
Table 2 – Channel status data format
Byte
0 a b
bit 0 1 2 3 4 5 6 7
bit 8 9 10 11 12 13 14 15
bit 16 17 18 19 20 21 22 23
bit 24 25 26 27 28 29 30 31
bit 32 33 34 35 36 37 38 39
bit 40 41 42 43 44 45 46 47
bit 48 49 50 51 52 53 54 55
bit 56 57 58 59 60 61 62 63
bit 64 65 66 67 68 69 70 71
bit 72 73 74 75 76 77 78 79
bit 80 81 82 83 84 85 86 87
bit 88 89 90 91 92 93 94 95
bit 96 97 98 99 100 101 102 103
...

IEC 60958-1
Edition 4.0 2021-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Digital audio interface –
Part 1: General
Interface audionumérique –
Partie 1: Généralités
IEC 60958-1:2021-09(en-fr)
---------------------- Page: 1 ----------------------
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All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form

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About the IEC

The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes

International Standards for all electrical, electronic and related technologies.
About IEC publications

The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the

latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform IEC online collection - oc.iec.ch

The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the

variety of criteria (reference number, text, technical publications previews. With a subscription you will always have

committee, …). It also gives information on projects, replaced access to up to date content tailored to your needs.

and withdrawn publications.
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---------------------- Page: 2 ----------------------
IEC 60958-1
Edition 4.0 2021-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Digital audio interface –
Part 1: General
Interface audionumérique –
Partie 1: Généralités
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.160.01 ISBN 978-2-8322-1053-0

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

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 60958-1:2021 © IEC 2021
CONTENTS

FOREWORD ........................................................................................................................... 4

1 Scope .............................................................................................................................. 6

2 Normative references ...................................................................................................... 6

3 Terms and definitions ...................................................................................................... 6

4 Interface format ............................................................................................................... 8

4.1 Structure of format .................................................................................................. 8

4.1.1 Sub-frame format ............................................................................................. 8

4.1.2 Frame format ................................................................................................... 9

4.2 Channel coding ..................................................................................................... 10

4.3 Preambles ............................................................................................................ 10

4.4 Validity bit ............................................................................................................. 11

5 Channel status .............................................................................................................. 11

5.1 General ................................................................................................................. 11

5.2 Applications .......................................................................................................... 11

5.3 General assignment of the first and second channel status bits ............................ 11

5.4 Category code ...................................................................................................... 12

6 User data....................................................................................................................... 14

6.1 General ................................................................................................................. 14

6.2 Applications .......................................................................................................... 14

6.2.1 Professional use ............................................................................................ 14

6.2.2 Consumer use ............................................................................................... 14

7 Electrical requirement .................................................................................................... 14

7.1 Consumer application ........................................................................................... 14

7.1.1 General ......................................................................................................... 14

7.1.2 Timing accuracy ............................................................................................ 14

7.1.3 Unbalanced line ............................................................................................. 15

7.2 Professional application ........................................................................................ 18

8 Optical requirements ..................................................................................................... 18

8.1 Consumer application ........................................................................................... 18

8.1.1 Configuration of optical connection ................................................................ 18

8.1.2 Optical connector........................................................................................... 18

8.2 Professional applications ...................................................................................... 19

Annex A (informative) The use of the validity bit .................................................................. 20

Annex B (informative) Application documents and specifications .......................................... 21

Annex C (informative) A relationship of the IEC 60958 series families .................................. 22

Annex D (informative) Transmission of CD data other than linear PCM audio ...................... 24

Annex E (informative) The IEC 60958 series conformant data format ................................... 25

Annex F (informative) Stream change .................................................................................. 26

Annex G (informative) Characteristics of optical connection ................................................. 28

Bibliography .......................................................................................................................... 30

Figure 1 – Sub-frame format (linear PCM application) ............................................................. 9

Figure 2 – Frame format ......................................................................................................... 9

Figure 3 – Channel coding .................................................................................................... 10

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IEC 60958-1:2021 © IEC 2021 – 3 –

Figure 4 – Preamble M (shown as 11100010) ....................................................................... 11

Figure 5 – Simplified example of the configuration of the circuit (unbalanced) ....................... 15

Figure 6 – Rise and fall times ............................................................................................... 16

Figure 7 – Intrinsic jitter measurement filter .......................................................................... 16

Figure 8 – Eye diagram ......................................................................................................... 17

Figure 9 – Receiver jitter tolerance template ......................................................................... 17

Figure 10 – Basic optical connection ..................................................................................... 18

Figure C.1 – Relationships of the IEC 60958 families ............................................................ 22

Figure F.1 – Audio sources and AV receiver model ............................................................... 26

Figure F.2 – Switching from linear PCM to non linear PCM ................................................... 26

Figure F.3 – Switching from non linear PCM to linear PCM ................................................... 27

Figure F.4 – Switching from non-linear PCM to non-linear PCM ............................................ 27

Table 1 – Preamble coding ................................................................................................... 10

Table 2 – Channel status data format ................................................................................... 13

Table B.1 – Application documents and specifications .......................................................... 21

Table C.1 – data_type values and application ....................................................................... 23

Table G.1 – Characteristics of standard optical connection (optical interface) ....................... 28

Table G.2 – Characteristics of optical transmitter (optical interface) ...................................... 28

Table G.3 – Characteristics of optical receiver (optical interface) .......................................... 29

Table G.4 – Characteristics of fibre optic cable ..................................................................... 29

Table G.5 – Optical power budget for the link with plastic fibre ............................................. 29

---------------------- Page: 5 ----------------------
– 4 – IEC 60958-1:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DIGITAL AUDIO INTERFACE –
Part 1: General
FOREWORD

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

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international

co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and

in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,

Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their

preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with

may participate in this preparatory work. International, governmental and non-governmental organizations liaising

with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for

Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence between

any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent

rights. IEC shall not be held responsible for identifying any or all such patent rights.

IEC 60958-1 has been prepared by technical area 20: Analogue and digital audio, of IEC

technical committee 100: Audio, video and multimedia systems and equipment. It is an

International Standard.

This fourth edition cancels and replaces the third edition published in 2008, and

Amendment 1:2014. This edition constitutes a technical revision.

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

edition:
a) The relevant part of IEC 60958-5 is supported.
---------------------- Page: 6 ----------------------
IEC 60958-1:2021 © IEC 2021 – 5 –
The text of this International Standard is based on the following documents:
Draft Report on voting
100/3544/CDV 100/3593/RVC

Full information on the voting for its approval can be found in the report on voting indicated in

the above table.
The language used for the development of this International Standard is English.

A list of all parts of the IEC 60958 series, under the general title Digital audio interface, can be

found on the IEC website.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in

accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available

at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are

described in greater detail at www.iec.ch/standardsdev/publications.

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

stability date indicated on the IEC website under 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.
---------------------- Page: 7 ----------------------
– 6 – IEC 60958-1:2021 © IEC 2021
DIGITAL AUDIO INTERFACE –
Part 1: General
1 Scope

This part of IEC 60958 describes a serial, uni-directional, self-clocking interface for the

interconnection of digital audio equipment for consumer and professional applications.

It provides the basic structure of the interface. Separate documents define items specific to

particular applications.

The interface is primarily intended to carry monophonic or stereophonic programmes, encoded

using linear PCM and with a resolution of up to 24 bits per sample.

When used for other purposes, the interface is able to carry audio data coded other than as

linear PCM coded audio samples. Provision is also made to allow the interface to carry data

related to computer software, multimedia technologies, or signals coded using non-linear PCM.

The format specification for these applications is not part of this document.

The interface is intended for operation at audio sampling frequencies of 32 kHz and above.

Auxiliary information is transmitted along with the programme.
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 60268-11:1987, Sound system equipment – Part 11: Application of connectors for the

interconnection of sound system components
IEC 60958-3, Digital audio interface – Part 3: Consumer applications

IEC 60958-4 (all parts), Digital audio interface – Part 4: Professional applications

IEC 60958-5, Digital audio interface – Part 5: Consumer application enhancement
3 Terms and definitions
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
sampling frequency
frequency of the samples representing an audio signal
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IEC 60958-1:2021 © IEC 2021 – 7 –

Note 1 to entry: When more than one signal is transmitted through the same interface, the sampling frequencies

are identical.
3.2
audio sample word

value of a digital audio sample; representation is linear in 2's complement binary form

Note 1 to entry: Positive numbers correspond to positive analogue voltages at the input of the analogue-to-digital

converter (ADC).
3.3
auxiliary sample bit

four least significant bits (LSBs) which can be assigned as auxiliary sample bits and used for

auxiliary information when the number of audio sample bits in the main data field is less than

or equal to 20
3.4
validity bit

bit indicating whether the main data field bits in the sub-frame (time slots 4 to 27 or 8 to 27,

depending on the audio word length as described in 4.1.1) are reliable or not
3.5
channel status

data carrying, in a fixed format, information associated with each main data field channel which

is decodable by any interface user

Note 1 to entry: Examples of information to be carried in the channel status are: length of audio sample words, pre-

emphasis, sampling frequency, time codes, alphanumeric source and destination codes.

3.6
user data
data provided to carry any other information
3.7
parity bit

bit provided to permit the detection of an odd number of errors resulting from malfunctions in

the interface
3.8
preamble
specific patterns used for synchronization
Note 1 to entry: There are three different preambles (see 4.3).
3.9
sub-frame
fixed structure used to carry information (see 4.1.1 and 4.1.2)
3.10
frame
sequence of two successive and associated sub-frames
3.11
block
group of 192 consecutive frames

Note 1 to entry: The start of a block is designated by a special sub-frame preamble (see 4.3).

3.12
channel coding

coding method by which the binary digits are represented for transmission through the interface

---------------------- Page: 9 ----------------------
– 8 – IEC 60958-1:2021 © IEC 2021
3.13
unit interval (UI)
shortest nominal time interval in the coding scheme
Note 1 to entry: There are 128 UI in a sample frame.
3.14
interface jitter

deviation in the timing of interface data transitions (zero crossings) when compared with an

ideal clock
3.15
intrinsic jitter

output interface jitter of a device that is either free-running or is synchronized to a jitter-free

reference
3.16
jitter gain

ratio of the amplitude of jitter components at the output to their amplitude at the synchronization

input to the device under test
4 Interface format
4.1 Structure of format
4.1.1 Sub-frame format

Each sub-frame is divided into 32 time slots, numbered from 0 to 31 (see Figure 1).

Time slots 0 to 3 (preambles) carry one of the three permitted preambles (see 4.1.2 and 4.3;

also see Figure 2).

Time slots 4 to 27 (main data field) carry the audio sample word in linear 2's complement

representation. The most significant bit (MSB) is carried by time slot 27.
When a 24-bit coding range is used, the LSB is in time slot 4 (see Figure 1).

When a 20-bit coding range is used, time slots 8 to 27 carry the audio sample word with the LSB

in time slot 8. Time slots 4 to 7 may be used for other applications. Under these circumstances,

the bits in the time slots 4 to 7 are designated auxiliary sample bits (see Figure 1).

If the source provides fewer bits than the interface allows (either 20 or 24), the unused LSBs

are set to a logical "0".

For a non-linear PCM audio application or a data application the main data field may carry any

other information.

Time slot 28 (validity bit) carries the validity bit associated with the main data field (see 4.4).

Time slot 29 (user data bit) carries 1 bit of the user data channel associated with the main data

field channel transmitted in the same sub-frame. For the applications, refer to the other parts

of IEC 60958.

Time slot 30 (channel status bit) carries 1 bit of the channel status information associated with

the main data field channel transmitted in the same sub-frame. For details refer to the other

parts of IEC 60958.
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IEC 60958-1:2021 © IEC 2021 – 9 –

Time slot 31 (parity bit) carries a parity bit such that time slots 4 to 31 inclusive carry an even

number of ones and an even number of zeroes (even parity).
NOTE The preambles have even parity as an explicit property.
Figure 1 – Sub-frame format (linear PCM application)

Annex E describes the IEC 60958 series conformant data format that utilises the sub-frame

format.
4.1.2 Frame format

A frame is uniquely composed of two sub-frames (see Figure 2). For linear coded audio

applications, the rate of transmission of frames normally corresponds exactly to the source

sampling frequency.

In 2-channel operation mode, the samples taken from both channels are transmitted by time

multiplexing in consecutive sub-frames. The first sub-frame (left or "A" channel in stereophonic

operation and primary channel in monophonic operation) normally starts with preamble "M".

However, the preamble changes to preamble "B" once every 192 frames to identify the start of

the block structure used to organize the channel status information. The second sub-frame

(right or "B" channel in stereophonic operation and secondary channel in monophonic operation)

always starts with preamble "W".

In single channel operation mode in a professional application, the frame format is the same as

in the 2-channel mode. Data is carried in the first sub-frame and may be duplicated in the

second sub-frame. If the second sub-frame is not carrying duplicate data, then time slot 28,

(validity flag) shall be set to logical "1".

NOTE For historical reasons preambles "B", "M" and "W" are, for use in professional applications, referred to as

"Z", "X" and "Y", respectively.

Annex C describes the relation of the IEC 60958 series families based on the frame format.

Figure 2 – Frame format
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– 10 – IEC 60958-1:2021 © IEC 2021
4.2 Channel coding

To minimize the direct current (d.c.) component on the transmission line, to facilitate clock

recovery from the data stream and to make the interface insensitive to the polarity of

connections, time slots 4 to 31 are encoded in biphase-mark.

Each bit to be transmitted is represented by a symbol comprising two consecutive binary states.

The first state of a symbol is always different from the second state of the previous symbol. The

second state of the symbol is identical to the first if the bit to be transmitted is logical "0".

However, it is different if the bit is logical "1" (see Figure 3).
Figure 3 – Channel coding
4.3 Preambles

Preambles are specific patterns providing synchronization and identification of the sub-frames

and blocks.

To achieve synchronization within one sampling period and to make this process completely

reliable, these patterns violate the biphase-mark code rules, thereby avoiding the possibility of

data imitating the preambles.

A set of three preambles is used. These preambles are transmitted in the time allocated to four

time slots at the start of each sub-frame (time slots 0 to 3), and are represented by eight

successive states. The first state of the preamble is always different from the second state of

the previous symbol (representing the parity bit). Depending on this state, the preambles are

as shown in Table 1.
Table 1 – Preamble coding
Preceding state 0 1
Preamble code Channel coding
"B" or "Z" 11101000 00010111 Sub-frame 1 and
(see note to 4.1.2) the start of the block
"M" or "X" 11100010 00011101 Sub-frame 1
"W" or "Y" 11100100 00011011 Sub-frame 2

Like biphase code, these preambles are d.c. free and provide clock recovery. They differ in at

least two states from any valid biphase sequence.
Figure 4 represents preamble "M".

NOTE Owing to the even-parity bit in time slot 31, all preambles start with a transition in the same direction

(see 4.1.1). Thus, only one of these sets of preambles is, in practice, transmitted through the interface. However, it

is necessary for both sets to be decodable because either polarity is possible in a connection.

---------------------- Page: 12 ----------------------
IEC 60958-1:2021 © IEC 2021 – 11 –
Figure 4 – Preamble M (shown as 11100010)
4.4 Validity bit

The validity bit is logical "0" if the information in the main data field is reliable, and it is logical

"1" if it is not. There is no default state for the validity bit.

NOTE For transmissions not using a linear PCM coding, this bit can be set. This is intended to prevent accidental

decoding of non-audio d
...

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