IEC 60958-4-1:2016

Digital audio interface - Part 4-1: Professional applications - Audio content

IEC 60958-4-1:2016 specifies the format for coding audio used for the audio content. Together with IEC 60958-1, IEC 60958-4-2, and IEC 60958-4-4, it specifies an interface for serial digital transmission of two channels of periodically sampled and linearly represented digital audio data from one transmitter to one receiver. This first edition, together with IEC 60958-4-2 and IEC 60958-4-4, cancels and replaces IEC 60958-4 published in 2003 and its Amendment 1:2008 and constitutes a technical revision. This edition includes the following significant technical changes with respect to IEC 60958-4:2003 with its Amendment 1:2008:
- support for a wider range of physical media;
- support for a wider range of audio sampling frequencies;
- deprecation of "minimum implementation" of channel status data.

Interface audionumérique - Partie 4-1: Applications professionnelles - Contenu audio

L'IEC 60958-4-1:2016 spécifie le format de codage audio utilisé pour le contenu audio. Cette partie, avec l'IEC 60958-1, l'IEC 60958-4-2 et l'IEC 60958-4-4, précise une interface de transmission numérique en série de deux voies de données audionumériques échantillonnées de façon périodique et représentées de façon linéaire entre un émetteur et un récepteur. Cette première édition, avec l'IEC 60958-4-2 et l'IEC 60958-4-4, annule et remplace l'IEC 60958-4 parue en 2003 et l'Amendement 1:2008 et constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'IEC 60958-4:2003 et son Amendement 2008:
- prise en charge d'une gamme plus large de supports physiques;
- prise en charge d'une gamme plus large de fréquences d'échantillonnage audio;
- "mise en oeuvre minimale" des données de la voie de signalisation déconseillée.

General Information

• Status: Published
• Publication Date: 23-Mar-2016
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 33.100 - Electromagnetic compatibility (EMC)
• ICS: 33.160.30 - Audio systems
• Technical Committee: TC 100 - Audio, video and multimedia systems and equipment
• Current Stage: PPUB - Publication issued
• Start Date: 30-Apr-2016
• Completion Date: 24-Mar-2016

Standards Content (Sample)

IEC 60958-4-1
®

Edition 1.0 2016-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE


Digital audio interface –
Part 4-1: Professional applications – Audio content

Interface audionumérique –
Partie 4-1: Applications professionnelles – Contenu audio

IEC 60958-4-1:2016-03(en-fr)

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IEC 60958-4-1

®


Edition 1.0 2016-03




INTERNATIONAL



STANDARD




NORME



INTERNATIONALE











Digital audio interface –

Part 4-1: Professional applications – Audio content




Interface audionumérique –

Partie 4-1: Applications professionnelles – Contenu audio
















INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

ELECTROTECHNIQUE


INTERNATIONALE




ICS 33.160.30 ISBN 978-2-8322-3232-3



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

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– 2 – IEC 60958-4-1:2016 © IEC 2016
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references. 6
3 Terms and definitions . 6
4 Audio content . 7
4.1 Audio content coding . 7
4.2 PCM polarity . 7
4.3 Coding precision options . 7
4.4 Intermediate coding precision . 8
4.5 Non-audio content . 8
4.6 DC content . 8
5 Sampling frequency . 8
5.1 Channel interdependency . 8
5.2 Choice of sampling frequency . 8
6 Validity bit . 8
6.1 Channel validity usage . 8
6.2 Independent channel validity . 8
7 Pre-emphasis . 8
7.1 Pre-emphasis characteristic . 8
7.2 Pre-emphasis indication . 9
Bibliography . 10

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IEC 60958-4-1:2016 © IEC 2016 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_______________

DIGITAL AUDIO INTERFACE –

Part 4-1: Professional applications – Audio content

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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60958-4-1 has been prepared by technical area 4: Digital system
interfaces and protocols, of IEC technical committee 100: Audio, video and multimedia
systems and equipment.
This first edition, together with IEC 60958-4-2 and IEC 60958-4-4, cancels and replaces
IEC 60958-4 published in 2003 and its Amendment 1:2008 and constitutes a technical
revision.
This edition includes the following significant technical changes with respect to
IEC 60958-4:2003 with its Amendment 1:2008:
a) support for a wider range of physical media;
b) support for a wider range of audio sampling frequencies;
c) deprecation of “minimum implementation” of channel status data.

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– 4 – IEC 60958-4-1:2016 © IEC 2016
The text of this standard is based on the following documents:
CDV Report on voting
100/2452/CDV 100/2581/RVC

Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
A list of all parts in the IEC 60958 series, published under the general title Digital audio
interface, can be found on the IEC website.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended

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IEC 60958-4-1:2016 © IEC 2016 – 5 –
INTRODUCTION
The two-channel digital audio interface has been widely used in a variety of professional
audio applications that have reached beyond the vision of the original standard. In particular,
applications using increased sampling frequencies and alternative physical media.
Separating the standard into independently-maintainable parts allows, for example, additional
transmission media to be introduced in the future by revising IEC 60958-4-4 without affecting
the other parts of the IEC 60958-4 series. The parts comprise:
Part 4-1: Audio content: defines the format for coding audio used for the audio content. It
specifies the semantics of the audio data, including the validity flag. It also
specifies the sampling frequency by reference to AES5.
Part 4-2: Metadata and subcode: specifies the format for information, metadata, or subcode
transmitted with the audio data: principally the channel status but also user data
and the auxiliary bits. Implementors will note that the current implementation
options ("Standard" and "Enhanced") both require that status data be
implemented correctly in compliant equipment.
Part 4-4: Physical and electrical parameters: specifies the physical signals that convey the
bit stream specified in IEC 60958-1. The transport format is intended for use with
shielded twisted-pair cable of conventional design over distances of up to 100 m
at frame rates of up to 50 kHz. Longer cable lengths and higher frame rates may
be used, but with a rapidly increasing requirement for care in cable selection and
possible receiver equalization, or the use of active repeaters. Provision is made in
this standard for adapting the balanced terminals to use 75 Ω coaxial cable.
Transmission by fibre-optic cable is under consideration.

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– 6 – IEC 60958-4-1:2016 © IEC 2016
DIGITAL AUDIO INTERFACE –

Part 4-1: Professional applications – Audio content



1 Scope
This part of IEC 60958 specifies the format for coding audio used for the audio content.
Together with IEC 60958-1, IEC 60958-4-2, and IEC 60958-4-4, it specifies an interface for
serial digital transmission of two channels of periodically sampled and linearly represented
digital audio data from one transmitter to one receiver.
It is expected that the audio data will have been sampled at any of the sampling frequencies
recognized by AES5. The capability of the interface to indicate other sample rates does not
imply that it is recommended that equipment support these rates. To eliminate doubt,
equipment specifications should define supported sampling frequencies.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60958-1, Digital audio interface – Part 1: General
IEC 60958-4-2, Digital audio interface – Part 4-2: Professional applications – Metadata and
subcode
IEC 60958-4-4, Digital audio interface – Part 4-4: Professional applications – Physical and
electrical parameters
ITU-R Recommendation BS.450-3, Transmission standards for FM sound broadcasting at
VHF
ITU-T Recommendation J.17, Pre-emphasis used on sound-program circuits
AES5-2008 (r2013), AES recommended practice for professional digital audio – Preferred
sampling frequencies for applications employing pulse-code modulation http://www.aes.org/
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
sampling frequency
frequency of the samples representing an audio signal
Note 1 to entry: See 5.2.

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IEC 60958-4-1:2016 © IEC 2016 – 7 –
3.2
audio sample word
series of binary digits representing the amplitude of an audio sample, also known as a PCM
sample
Note 1 to entry: See 4.1.
3.3
auxiliary sample bits
the four least significant bits (LSBs) of those allocated to audio which can be assigned as
auxiliary sample bits and used for auxiliary information when the number of audio sample bits
is less than or equal to 20
Note 1 to entry: This note applies to the French language only.
3.4
validity bit
bit indicating whether the audio sample bits in the same subframe are suitable for direct
conversion to an analogue audio signal
3.5
MSB
most significant bit of an audio sample word, being the sign bit in the case of two’s
complement code
Note 1 to entry: This note applies to the French language only.
3.6
LSB
least significant bit of an audio sample word
Note 1 to entry: This note applies to the French language only.
3.7
subframe
smallest structural element in a digital audio interface transport stream, carrying one PCM
sample and ancillary information
Note 1 to entry: See IEC 60958-1.
4 Audio content
4.1 Audio content coding
The audio content shall be coded as linear PCM using 2’s complement code.
4.2 PCM polarity
Positive analogue voltages at the ADC input shall be represented by positive binary numbers.
4.3 Coding precision options
The accuracy of the coding shall be between 16 bit and 24 bit, in two ranges so as to indicate
which length is in use in channel status data, 16 bit to 20 bit and 20 bit to 24 bit (see
IEC 60958-4-2).

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– 8 – IEC 60958-4-1:2016 © IEC 2016
4.4 Intermediate coding precision
The interface permits maximum word lengths of either 20 bit or 24 bit. A source which
provides fewer bits than this shall be justified to the MSB of the available word length and the
unused LSBs shall be set to logic 0.
NOTE If a low-resolution signal were not so justified, then sign extension would be needed.
4.5 Non-audio content
The interface may alternatively carry data or audio which is compressed or in a different
format in place of linear PCM audio, in either channel B or both channels. In such cases the
validity bit shall be set independently in each channel and channel status encoded to indicate
this. See IEC 60958-4-2.
NOTE This use is not standardized here. Provision is only made to protect standard equipment from this type of
use.
4.6 DC content
The coded audio shall contain as little equivalent DC offset as possible, and in any case less
than the analogue equivalent noise level.
5 Sampling frequency
5.1 Channel interdependency
The sampling frequency shall be the same in both channels.
5.2 Choice of sampling frequency
The sampling frequency shall be in accordance with AES5-2008.
6 Validity bit
6.1 Channel validity usage
The validity bit shall be set to logic 0 if the associated audio sample word is suitable for direct
conversion to an analogue audio signal, and shall be set to logic 1 if it is not suitable. Where
channel status indicates (in byte 0 bit 1, see IEC 60958-4-2) that the audio sample word is not
in linear PCM form, the validity bit shall be set to logic 1 in every subframe.
There is no default state for the validity bit.
6.2 Independent channel validity
Validity shall be set or reset for each and every sample independently in each channel.
7 Pre-emphasis
7.1 Pre-emphasis characteristic
The audio signal may be
...