IEC 61937-1:2021

Digital audio - Interface for non-linear PCM encoded audio bitstreams applying IEC 60958 - Part 1: General

IEC 61937-1:2021 is available as IEC 61937-1:2021 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.IEC 61937-1:2021 applies to the digital audio interface using the IEC 60958 series for the conveying of non-linear PCM encoded audio bitstreams.
It describes the way in which this digital interface can be used in consumer applications. The professional mode is not considered within the scope of this document.
IEC 61937-1:2021 cancels and replaces the second edition published in 2007, and amendment 1 published in 2011. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
a) Activation of Pe field;
b) Enhanced usage of channel status bits.
c) Addition of Annex B.

Audionumérique - Interface pour les flux de bits audio à codage MIC non linéaire conformément à l'IEC 60958 - Partie 1: Généralités

IEC 61937-1:2021 est disponible sous forme de IEC 61937-1:2021 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.L'IEC 61937-1:2021 s'applique à l'interface audionumérique conforme à la série IEC 60958 pour l'acheminement des flux de bits audio à codage MIC non linéaire. Elle décrit comment cette interface numérique peut être utilisée dans les applications grand public. Le domaine d'application du présent document ne couvre pas le mode professionnel. L'IEC 61937-1:2021 annule et remplace la deuxième édition parue en 2007 et l'Amendement 1:2011. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) activation du champ Pe;
b) utilisation élargie de la voie de signalisation;
c) ajout de l'Annexe B.

General Information

• Status: Published
• Publication Date: 23-Feb-2021
• ICS: 33.160.30 - Audio systems
• Technical Committee: TC 100 - Audio, video and multimedia systems and equipment
• Current Stage: PPUB - Publication issued
• Completion Date: 24-Feb-2021

Standards Content (Sample)

IEC 61937-1
®

Edition 3.0 2021-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
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Digital audio – Interface for non-linear PCM Encoded audio bitstreams applying
IEC 60958 –
Part 1: General

Audionumérique – Interface pour les flux de bits audio à codage MIC non
linéaire selon l'IEC 60958 –
Partie 1: Généralités

IEC 61937-1:2021-02(en-fr)

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IEC 61937-1

®


Edition 3.0 2021-02




INTERNATIONAL



STANDARD




NORME


INTERNATIONALE
colour

inside










Digital audio – Interface for non-linear PCM Encoded audio bitstreams applying

IEC 60958 –

Part 1: General



Audionumérique – Interface pour les flux de bits audio à codage MIC non

linéaire selon l'IEC 60958 –


Partie 1: Généralités













INTERNATIONAL

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ICS 33.160.30 ISBN 978-2-8322-9429-1




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CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms, definitions, and presentation . 6
3.1 Terms and definitions . 6
3.2 Presentation convention . 8
4 General description . 8
5 Interface format . 8
6 Mapping of the audio bitstream on to IEC 60958 . 9
6.1 Coding of the bitstream . 9
6.2 Burst-payload . 14
6.3 Stuffing . 15
7 Format of data-bursts . 15
7.1 General . 15
7.2 Pause data-burst . 16
7.3 Audio data-bursts . 19
7.4 Null data-burst . 19
Annex A (normative) Channel status when IEC 60958 is used in consumer
applications . 20
Annex B (informative) Monaural linear PCM audio sample simultaneous transferred
with non-linear PCM encoded audio bitstream . 21

Figure 1 – IEC 60958 interface format . 9
Figure 2 – Data-burst format . 11
Figure 3 – Burst-preamble . 11
Figure 4 – Burst-preamble with extended preamble . 13
Figure 5 – Length of the burst-payload specified by Pd . 14
Figure 6 – Burst spacing . 15
Figure 7 – Flow chart of transmission of a bitstream . 16
Figure 8 – Bridging gaps in-between data-bursts with three pause data-bursts . 17
Figure 9 – Data-burst format of the data-type pause . 18
Figure 10 – Null data-burst . 19
Figure B.1 – Frame and Block structure . 21
Figure B.2 – Example 1: Frame and Block structure @ 48 kHz IEC 60958 frame rate . 22
Figure B.3 – Example 2: Frame and Block structure @ 192 kHz IEC 60958 frame rate . 22

Table 1 – Bit allocation of the IEC 60958 frame . 9
Table 2 – Bit allocation of data-burst in IEC 60958 subframes . 10
Table 3 – Burst-preamble words . 12
Table 4 – Bit map of burst-preambles . 12
Table 5 – Fields of burst-info . 12
Table 6 – Burst-preamble words . 13
Table 7 – Fields of Pe (extended data-type) . 13

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IEC 61937-1:2021 © IEC 2021 – 3 –
Table 8 – Fields of Pf . 13
Table 9 – Values of data-type-dependent info of the pause data-burst . 18
Table 10 – Burst-payload of pause data-burst . 18
Table 11 – Fields of a null data-burst . 19
Table A.1 – Allocation of the channel status bits . 20
Table B.1 – Relationship between sampling frequency for monaural linear PCM and
IEC 60958 frame rate for non-linear PCM . 23

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INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

DIGITAL AUDIO –
INTERFACE FOR NON-LINEAR PCM ENCODED
AUDIO BITSTREAMS APPLYING IEC 60958 –

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
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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.
IEC 61937-1 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 third edition cancels and replaces the second edition published in 2007, and
amendment 1 published in 2011. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Activation of Pe field;
b) Enhanced usage of channel status bits.
c) Addition of Annex B.

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IEC 61937-1:2021 © IEC 2021 – 5 –
The text of this International Standard is based on the following documents:
Draft Report on voting
100/3447/CDV 100/3522/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.
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 list of all the parts of IEC 61937, 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 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.

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DIGITAL AUDIO –
INTERFACE FOR NON-LINEAR PCM ENCODED
AUDIO BITSTREAMS APPLYING IEC 60958 –

Part 1: General



1 Scope
This part of IEC 61937 applies to the digital audio interface using the IEC 60958 series for the
conveying of non-linear PCM encoded audio bitstreams.
It describes the way in which this digital interface can be used in consumer applications.
The professional mode is not considered within the scope of this document.
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 60958-1, Digital audio interface – Part 1: General
IEC 60958-3, Digital audio interface – Part 3: Consumer applications
IEC 60958-5, Digital audio interface – Part 5: Consumer application enhancement
IEC 61937-2, Digital audio – Interface for non-linear PCM encoded audio bitstreams applying
IEC 60958 – Part 2: Burst-info
3 Terms, definitions, and presentation
For the purposes of this document, the following terms, definitions, and presentation
convention 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 Terms and definitions
3.1.1
audio data-burst
data-burst with an encoded audio frame as burst-payload
3.1.2
audio data-word
16-bit data word

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IEC 61937-1:2021 © IEC 2021 – 7 –
3.1.3
audio frame
fixed number of audio samples
Note 1 to entry: The number of samples in an audio frame is dependent on the particular encoding system that is
used to encode the audio frame into the encoded audio frame.
3.1.4
audio gap
period in the sequence of baseband audio samples where valid samples of audio are not
available
3.1.5
bitstream
non-linear PCM encoded audio source, represented in a sequence of bits
Note 1 to entry: In this interface, the bitstream consists of a sequence of data-bursts.
3.1.6
data-burst
packet of data, including the burst-preamble, to be transmitted across the interface
3.1.7
burst-payload
information content of the data-burst
3.1.8
burst-preamble
header for the data-burst, containing synchronization, and information about the data
contained in the burst-payload
3.1.9
data-type
reference to the type of payload of the data-bursts
3.1.10
encoded audio frame
minimum decodable unit of an encoded data sequence
Note 1 to entry: Each encoded audio frame is the encoded representation of a fixed number of audio samples (for
each original audio channel). The number of samples that are encoded into an encoded audio frame depends on
the particular encoding system that is used to encode the audio frame into the encoded audio frame.
3.1.11
idle
state in which the interface is not used to convey any sequence of data-bursts or PCM data
Note 1 to entry: The channel status data is still active (bit b1 is set to '1' when further non-linear PCM encoded
audio is anticipated; see Figure 7).
3.1.12
length-code
code indicating the length of the data-burst-payload in bits, bytes or 8-byte units
3.1.13
repetition period
period between the reference point of the current data-burst and the reference point of the
immediately following data-burst of the same data-type

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3.1.14
sampling frequency
sampling frequency of the encoded PCM audio samples (i.e. before encoding and after
decoding)
3.1.15
sampling period
time period related to the sampling frequency of the PCM audio samples, represented in the
encoded bitstream
3.1.16
stuffing
occupying the unused data capacity of the interface
3.1.17
stuffing subframe
occupying the unused data capacity in 16-bit audio data words
3.1.18
stream gap
period within the encoded audio bitstream without any audio frame; a discontinuity in the
bitstream
Note 1 to entry: Typically, a stream gap will occur between encoded audio frames.
3.2 Presentation convention
3.2.1
F872h
value 'F872' in hexadecimal format
4 General description
The format of the IEC 60958 interface consists of a sequence of IEC 60958 subframes. Each
IEC 60958 subframe is normally used to carry one linear PCM sample, but may also be used
to convey data. The non-linear PCM encoded audio bitstreams to be transported over this
interface are formed into a sequence of data-bursts.
Each data-burst consists of a 64-bit burst-preamble, followed by the burst-payload. The burst-
preamble consists of a sync-word, information about the burst-payload and a bitstream-
number.
The interface may convey one or more bitstreams. Each type of bitstream may impose a
particular requirement for the repetition period for the data-bursts that make up the bitstream
(see Clause 7).
The 16 bits of a data-burst are placed in time-slots 12 to 27 of an IEC 60958 subframe. Both
odd and even IEC 60958 subframes (channel 1, channel 2) are simultaneously used to carry
32 bits of data. This allows IEC 60958, in the consumer mode, to convey either two-channel
linear PCM audio, or a set of non-linear PCM encoded bitstreams (alternating data words), but
not both simultaneously.
5 Interface format
The interface format as defined in IEC 60958-1 and IEC 60958-3 is used.

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IEC 61937-1:2021 © IEC 2021 – 9 –
6 Mapping of the audio bitstream on to IEC 60958
6.1 Coding of the bitstream
6.1.1 General
The non-linear PCM encoded audio bitstream is transferred using the basic 16-bit data area of
the IEC 60958 subframes, i.e. in time-slots 12 to 27 (see Figure 1 and Table 1). Because the
non-linear PCM encoded audio bitstream to be transported is at a lower data rate than that
supported by the IEC 60958 interface, the audio bitstream is broken into a sequence of
discrete data-bursts, and stuffing between the data-bursts is necessary (see 6.3).
Each data-burst contains data of an encoded audio frame that is the encoded representation
of a fixed number of audio samples per PCM audio channel. The number of samples to be
encoded into an encoded audio frame depends on the particular encoding system.
It is possible for this interface to simultaneously convey multiple non-linear PCM encoded
audio bitstreams. One of the applications of this capability would be to convey both a main
audio service and an associated audio service.

Figure 1 – IEC 60958 interface format
Table 1 – Bit allocation of the IEC 60958 frame
Field IEC 60958 time-slot Value
0 to 3 Preamble IEC 60958 preamble
4 to 7 Auxiliary field Not used, all "0" or partial of linear PCM
8 to 11 Unused data bits Not used, all "0" or partial of linear PCM
12 to 27 16-bit data Sections of the bitstream
28 Validity flag According to IEC 60958
29 User data According to IEC 60958
30 Channel status According to IEC 60958
31 Parity bit According to IEC 60958

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6.1.2 Bit map of bitstream
The method of placing the data into the IEC 60958 bitstream is to format the data to be
transmitted into data-bursts and to send each data-burst in a continuous sequence of
IEC 60958 frames (see Table 2).
Table 2 – Bit allocation of data-burst in IEC 60958 subframes
Bit of subframes
Subframe MSB  LSB
b27 b26 b25 ………… b14 b13 b12
Frame 0; subframe B or M 0 1 14 15
Frame 0; subframe W 16 17 30 31
Frame 1; subframe B or M 32 33 46 47
Frame 1; subframe W 48 49 62 63
Frame 2; subframe B or M 64 65 78 79
--------------------  ------------
Last subframe B or M of data-burst n – 32 n – 31 n – 18 n – 17
Last subframe W of data-burst n – 16 n – 15 n – 2 n – 1

Considering the data within an IEC 60958 subframe as a 16-bit word out of a serial stream of
bits, the first bit of the burst-payload in a data-burst would occupy the MSB of subframe 1
nd
(time-slot 27), and the 32 bit would occupy the LSB (or what would be the LSB for 16-bit
PCM audio) of subframe 2 (time-slot 12). The next 32 bits of the burst-payload would occupy
the next IEC 60958 frame. The last data bits of the audio data-burst might occupy only a
fraction of the last frame. Any unused bits in the last frame will be ignored by the receiver. In
the case where the audio data-burst contains a multiple of 16 bits, all used IEC 60958 sub-
frames are completely filled. When it is not a multiple of 16 bits, the bits of the burst-payload
to be conveyed in the last IEC 60958 subframe will be MSB aligned; the remaining bits shall
be stuffed with zeros.
6.1.3 IEC 60958 validity flag
It is recommended to set the validity bit to a logical '1'. This is intended to prevent accidental
decoding of non-audio data to analogue before a complete channel status block is received.
6.1.4 IEC 60958 channel status bit 1
The purpose of channel status bit 1 is to indicate if IEC 60958 is used to convey linear PCM
or to indicate that the interface is used for other purposes (see Annex A). This bit shall be set
to '1' when IEC 60958 is used to convey non-linear PCM encoded audio bitstreams.
6.1.5 Symbol frequency
When the IEC 60958 bitstream conveys linear PCM audio, the symbol frequency is 64 times
the PCM sampling frequency (32 time-slots per PCM sample, times two channels). When a
non-linear PCM encoded audio bitstream is conveyed by the interface, the symbol frequency
is normally 64 times the sampling rate of the encoded audio within that bitstream, and other
times should be referred to each parts of IEC 61937.
6.1.6 The format of the data-bursts
Each data-burst contains a burst-preamble consisting of four 16-bit words (Pa, Pb, Pc and Pd)
followed by the burst-payload that contains data of an encoded audio frame (see Figure 2).

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IEC 61937-1:2021 © IEC 2021 – 11 –

Figure 2 – Data-burst format
The repetition period of these bursts is defined as the length between the reference points R
(measured in IEC 60958 frames) of one data-burst and the next data-burst (with the same
bit-stream-number). The data representing each individual encoded audio frame is typically
specified to be packaged into a single individual data-burst, with a repetition period
(measured in IEC 60958 frames) for that data-burst equal to the number of encoded audio
samples of each channel contained within that encoded audio frame.
It is possible for a number of data-bursts representing multiple bitstreams to be interleaved on
the interface. When more than one non-linear PCM encoded audio bitstreams are transmitted
through the same interface, the audio sampling rates of these bitstreams are identical to each
other.
6.1.7 Burst-preamble
The burst-preamble consists of four mandatory fields. Pa and Pb represent a synchronization
word. Pc gives information about the type of data, and some information/control for the
receiver. Pd gives the length of the burst-payload, limited to 65 535 bits if the length of Pd is
given in bits, limited to 65 535 bytes if the length of Pd is given in bytes, or limited to 524 280
bytes if the length of Pd is given in 8-byte units.
The four preamble words are contained in two sequential IEC 60958 frames (see Figure 3).
The frame beginning the data-burst contains preamble word Pa in subframe 1, and Pb in
subframe 2. The next frame contains Pc in subframe 1 and Pd in subframe 2. When placed
into an IEC 60958 subframe, the MSB of a 16-bit burst-preamble word is placed into time-slot
27 and the LSB is placed into time-slot 12 (see Table 3 and Table 4).

Figure 3 – Burst-preamble

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Table 3 – Burst-preamble words
Value
Preamble word Length of field Contents
MSB . LSB
Pa 16-bit Sync word 1 F872h
Pb 16-b
...