IEC 61937-1:2007+AMD1:2011 CSV

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

IEC 61937-1:2007+A1:2011 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 (AES/EBU) is not considered within the scope of this standard. This second edition cancels and replaces the first edition published in 2000. It contains the following significant technical changes with respect to the previous edition:
- The data-type field in Pc is expanded from bit 0-4 to bit 0-6.
- A new additional definition of Pd is specified.
- The numbers of times for symbol frequency are changed to refer to each part of IEC 61937.
- The requirement for burst spacing is changed.
This bilingual version, published in 2011-04, corresponds to the English version. The French version of this standard has not been voted upon. This consolidated version consists of the second edition (2007) and its amendment 1 (2011). Therefore, no need to order amendment in addition to this publication.

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

La CEI 61937-1:2007+A1:2011 s'applique à l'interface audionumérique conforme à la série CEI 60958, pour l'acheminement des flux de bits audio à codage MIC non linéaire. Elle décrit la manière d'utiliser cette interface dans les applications grand public. Le domaine d'application de la présente norme ne couvre pas le domaine professionnel (AES/EBU). Cette seconde édition annule et remplace la première édition publiée en 2000. Elle contient les modifications techniques majeures suivantes par rapport à l'édition précédente:
- Le champ type-de-données dans Pc est étendu des bits 0 à 4 aux bits 0 à 6.
- Une nouvelle définition de Pd est spécifiée.
- Les coefficients de multiplication pour la fréquence des symboles sont changés pour faire référence à chaque partie de la CEI 61937.
- L'exigence sur l'espacement entre les salves est changée.
La présente version bilingue, publiée en 2011-04, correspond à la version anglaise. La version française de cette norme n'a pas été soumise au vote.  Cette version consolidée comprend la deuxième édition (2007) et son amendement 1 (2011). Il n'est donc pas nécessaire de commander l'amendement avec cette publication.

General Information

• Status: Published
• Publication Date: 14-Dec-2011
• ICS: 33.160.30 - Audio systems
• Technical Committee: TC 100 - Audio, video and multimedia systems and equipment
• Current Stage: DELPUB - Deleted Publication
• Completion Date: 24-Feb-2021

Standards Content (Sample)

IEC 61937-1 ®
Edition 2.1 2011-12
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 conformément à la CEI 60958 –
Partie 1: Généralités
IEC 61937-1:2007+A1:2011
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IEC 61937-1 ®
Edition 2.1 2011-12
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 conformément à la CEI 60958 –
Partie 1: Généralités
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX CH
ICS 33.160.30 ISBN 978-2-88912-795-50

– 2 – 61937-1  IEC:2007+A1:2011
CONTENTS
FOREWORD . 4
INTRODUCTION (to Amendment 1) . 6

1 Scope . 7
2 Normative references . 7
3 Terms, definitions, abbreviations and presentation . 7
3.1 Definitions . 7
3.2 Abbreviations . 9
3.3 Presentation convention . 9
4 General description . 9
5 Interface format . 10
6 Mapping of the audio bitstream on to IEC 60958 . 10
6.1 Coding of the bitstream . 10
6.2 Burst-payload . 16
6.3 Stuffing . 16
7 Format of data-bursts . 16
7.1 Pause data-burst . 18
7.2 Audio data-bursts . 20
7.3 Null data-burst . 20

Annex A (normative) Channel status when IEC 60958 is used in consumer
applications . 22

Bibliography . 23

Figure 1 – IEC 60958 interface format . 10
Figure 2 – Data-burst format . 12
Figure 3 – Burst-preamble . 12
Figure 4 – Burst-preamble with extended preamble . 14
Figure 5 – Length of the burst-payload specified by Pd . 15
Figure 6 – Burst spacing . 16
Figure 7 – Flow chart of transmission of a bitstream . 17
Figure 8 – Bridging gaps in-between data-bursts with three pause data-bursts . 18
Figure 9 – Data-burst format of the data-type pause . 19
Figure 10 – Null data-burst . 20

Table 1 – Bit allocation of the IEC 60958 frame . 10
Table 2 – Bit allocation of data-burst in IEC 60958 subframes . 11
Table 3 – Burst-preamble words . 13
Table 4 – Bit map of burst-preambles . 13
Table 5 – Fields of burst-info . 13
Table 6 – Burst-preamble words . 14
Table 7 – Fields of Pe (extended data-type) . 14

61937-1  IEC:2007+A1:2011 – 3 –
Table 8 – Fields of Pf . 14
Table 9 – Values of data-type-dependent info of the pause data-burst . 20
Table 10 – Burst-payload of pause data-burst . 20
Table 11 – Fields of a null data-burst . 21
Table A.1 – Allocation of the channel status bits . 22

– 4 – 61937-1  IEC:2007+A1:2011
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DIGITAL AUDIO –
INTERFACE FOR NON-LINEAR PCM ENCODED
AUDIO BITSTREAMS APPLYING IEC 60958 –

Part 1: General
FOREWORD
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This consolidated version of IEC 61937-1 consists of the second edition (2007)
[documents 100/1101/CDV and 100/1192/RVC] and its amendment 1 (2011) [documents
100/1810/CDV and 100/1883/RVC]. It bears the edition number 2.1.
The technical content is therefore identical to the base edition and its amendment and
has been prepared for user convenience. A vertical line in the margin shows where the
base publication has been modified by amendment 1. Additions and deletions are
displayed in red, with deletions being struck through.

61937-1  IEC:2007+A1:2011 – 5 –
International Standard IEC 61937-1 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 second edition of IEC 61937-1 cancels and replaces the first edition published in 2000.
This edition contains the following significant technical changes with respect to the previous
edition.
a) The data-type field in Pc is expanded from bit 0-4 to bit 0-6.
b) A new additional definition of Pd is specified.
c) The numbers of times for symbol frequency are changed to refer to each part of
IEC 61937.
d) The requirement for burst spacing is changed.

The bilingual version (2011-04) corresponds to the monolingual English version, published
in 2007-01.
The French version of this standard has not been voted upon.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
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 the base publication and its amendments will
remain unchanged until the stability date indicated on the IEC web site 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.
IMPORTANT – The “colour inside” logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this publication using a colour printer.

– 6 – 61937-1  IEC:2007+A1:2011
INTRODUCTION
(to Amendment 1)
The revision of IEC 61937-1 (2007) has become necessary to specify the additional definition
of length-code. Amendment 1 contains the following significant technical changes with respect
to the base publication (IEC 61937-1, second edition).
– New 8-bytes unit definition of length-code is added.
– An erratum in Clause 7 as for indication of the burst-payload type is corrected.

61937-1  IEC:2007+A1:2011 – 7 –
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 (AES/EBU) is not considered within the scope of this standard.
2 Normative references
The following referenced documents are indispensable for the application 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 (all parts), Digital audio interface
IEC 61937 (all parts), Digital audio – Interface for non-linear PCM encoded audio bitstreams
applying IEC 60958
3 Terms, definitions, abbreviations and presentation
For the purposes of this document, the following terms, definitions, abbreviations and
presentation convention apply.
3.1 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
3.1.3
audio frame
fixed number of audio samples
NOTE The number of samples in an audio frame is dependent on the particular encoding system which 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
– 8 – 61937-1  IEC:2007+A1:2011
3.1.5
bitstream
non-linear PCM encoded audio source, represented in a sequence of bits
NOTE 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 Each encoded audio frame is the encoded representation of a fixed number of audio samples (for each
original audio channel). The number of samples which are encoded into an encoded audio frame depends on the
particular encoding system which 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 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, or bytes or 8-bytes unit
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
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

61937-1  IEC:2007+A1:2011 – 9 –
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 Typically, a stream gap will occur between encoded audio frames.
3.2 Abbreviations
3.2.1
MPEG
Moving Pictures Expert Group, a joint committee of ISO and IEC
3.2.2
SMPTE
The Society of Motion Picture and Television Engineers
3.2.3
ETSI
European Telecommunication Standards Institute
3.2.4
ATSC
Advanced Television Standards Committee
3.3 Presentation convention
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 12-27 of an IEC 60958 subframe. Both odd
and even IEC 60958 subframes (ch1, ch2) 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.
– 10 – 61937-1  IEC:2007+A1:2011
5 Interface format
The interface format as defined in IEC 60958-1 and IEC 60958-3 is used.
6 Mapping of the audio bitstream on to IEC 60958
6.1 Coding of the bitstream
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. 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.
1 block = 192 frames
Frame 191 Frame 0 Frame 1 Frame 191 Frame 0
W B W M
Preamble Auxiliary LSB MSB V U C P
0 3 4 7 8 11 12 27 28 31
16-bit of bitstream
IEC  1288/03
Figure 1 – IEC 60958 interface format
Table 1 – Bit allocation of the IEC 60958 frame
Field IEC 60958 time-slot Value
0 – 3 Preamble IEC 60958 preamble
4 – 7 Auxiliary field Not used, all “0”
8 – 11 Unused data bits Not used, all “0”
12 – 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

61937-1  IEC:2007+A1:2011 – 11 –
6.1.1 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.
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
(time-slot 27), and the 32nd 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-bit, all used IEC 60958 sub-
frames are completely filled. When it is not a multiple of 16-bit, 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 ‘0’s.
6.1.2 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.
6.1.3 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.
6.1.4 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.
6.1.5 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 which contains data of an encoded audio frame.

– 12 – 61937-1  IEC:2007+A1:2011
Data-burst Stuffing Data-burst Stuffing Data-burst Stuffing Data-burst
...
Pa Pb Pc Pd Burst-payload Pa Pb Pc Pd
R
R
Repetition period between 2 data-bursts
IEC  1289/03
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 bitstream are transmitted
through the same interface, the audio sampling rates of these bitstreams are identical to each
other.
6.1.6 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 in the case of Pd
represent bits length, or limited to 65 535 bytes in the case of Pd represent bytes length.
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 in the case of Pd
represent bits length, limited to 65 535 bytes in the case of Pd represent bytes length or
limited to 524 280 bytes in the case of Pd represent 8-bytes unit length.
The four preamble words are contained in two sequential IEC 60958 frames. 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.
Pa Pb Pc Pd Burst_payload Pa Pb Pc Pd Burst_payload
Length of burst-payload
Length of burst-payload
Data-burst
Data burst
IEC  1290/03
Figure 3 – Burst-preamble
61937-1  IEC:2007+A1:2011 – 13 –
Table 3 – Burst-preamble words
Value
Preamble word Length of field Contents
MSB.LSB
Pa 16-bit Sync word 1 F872h
Pb 16-bit Sync word 2 4E1Fh
Pc 16-bit Burst-info Table 5
Pd 16-bit Length-code Number of bits, or number of
bytes or number of 8-bytes
unit according to data-type
Table 4 – Bit map of burst-preambles
IEC 60958 time-slot
27        12
bit-number
Preamble
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
bit-number
Pa 1 1 1 1 1 0 0 0 0 1 1 1 0 0 1 0
Pb 0 1 0 0 1 1 1 0 0 0 0 1 1 1 1 1
Pc According to Table 5, burst-info values Pc, bit 15 = MSB
Pd Length-code, bit 15 = MSB
6.1.7 Burst-info
The 16-bit burst-info contains information about the data which will be found in the data-burst.
Table 5 – Fields of burst-info
Bits of Pc Value Contents Remark
0 – 6 Data-type See IEC 61937-2
7 0 Error-flag indicating a valid burst-payload
1 Error-flag indicating that the burst-payload
may contain errors
8 – 12 Data-type-dependent info
13 – 15 0 Bitstream-number
NOTE The repetition period of pause data-bursts depends on the application in which IEC 60958 is used to
convey encoded audio bitstreams.

6.1.7.1 Data-type
The 7-bit data-type is defined in bits 0-6 of the burst-preamble Pc (see Table 5), bit 6 is
the MSB. This data-type field indicates the format of the burst-payload, which will be
conveyed in the data-burst. Typical properties of a data-type are the reference point and
repetition period of the burst, which is the number of sampling periods of the audio between
the reference point of the current data-burst and the reference point of the next data-burst.
The reference point is inherently defined for each data-type.
The allocation of data-types is defined in IEC 61937-2. The data-types themselves are
specified in each part of IEC 61937-3 and higher.

– 14 – 61937-1  IEC:2007+A1:2011
6.1.7.2 Extended data-type
When the burst-info Pc is equal to 1Fh (data-type = 31), the burst-preamble is extended with
Pe and Pf. Figure 4 shows a burst-preamble with an extended preamble. Pe and Pf are
included in the length of the burst-payload. The third frame of the IEC 60958 frames contains
Pe in subframe 1 and Pf in subframe 2.

L
Pa Pb Pd Pe Pf Burst_payload Pa Pb Pc Pd Pe Pf Burst_payload
Pc
Length of burst-payload
Length of burst-payload
Data-burst
Data burst
IEC  1291/03
Figure 4 – Burst-preamble with extended preamble
Table 6 – Burst-preamble words
Value
Preamble word length of field Contents
MSB.LSB
Pa 16-bit Sync word 1 F872h
Pb 16-bit Sync word 2 4E1Fh
Pc 16-bit Burst-info Table 5
Pd 16-bit Length-code Number of bits, or number of
bytes or number of 8-bytes
unit according to data-type
Pe (conditional) 16-bit Extended data-type Table 7
Pf (conditional) 16-bit Reserved for future use Table 8

6.1.7.2.1 Fields of Pe
Table 7 – Fields of Pe (extended data-type)
Repetition period
Reference
Bits of Pe Value Contents of data-burst in
point R
IEC 60958 frames
0 – 65 535 0 – 65 535 Extended data-type

The reference point and repetition period of data-bursts with extended data-type depend on
the properties of the data-type selected in the extension.
6.1.7.2.2 Fields of Pf
Table 8 – Fields of Pf
Bits of Pf value Contents
0 – 65 535 0 – 65 535 Reserved for future use

61937-1  IEC:2007+A1:2011 – 15 –
6.1.7.3 Error-flag
The error-flag bit is available to indicate if the contents of the data-burst contain data errors.
If a data-burst is thought to be error-free, or if the data source does not know if the data
contains errors, then the value of this bit is set to a ‘0’. If the data source does know that a
particular data-burst contains some errors this bit may be set to a ‘1’. The use of this bit by
receivers is optional.
6.1.7.4 Data-type-dependent info
The meaning of the 5-bit data-type-dependent info depends on the value of the data-type
(see 7.2).
6.1.7.5 Bitstream-number
The 3-bit bitstream-number indicates to which bitstream the data-burst belongs. Eight codes
(0-7) are available so that up to eight independent bitstreams may be multiplexed in one
bitstream in a time multiplex. Each independent bitstream shall use a unique bit-stream-
number. The MSB of the bit-stream-number is placed in bit number 15.
The following constraints apply. If a single bitstream is carried, the value of bitstream-number
is 0h. In the case where a main audio service and an associated audio service are placed into
this interface, the main service audio data-burst has its bitstream-number set to ‘0h’.
If a receiver is only capable of selecting and processing a single bitstream, it receives and
processes bitstream-number 0h. The bitstream with bitstream-number 0h thus has the highest
priority and should carry the most important data.
The data-type within a bitstream may change, but the bitstream-number is constant for a
bitstream; for example, the pause data-burst used to bridge a stream gap between data-burst
of an audio type contains the same bitstream-number.
6.1.8 Length-code
The length-code indicates the number of bits or bytes according to data-type within the data-
burst, from 0 to 65 535. The size of the Pa, Pb, Pc and Pd is not counted in the value of the
length-code. In other words, the length-code indicates the number of bits of the burst-payload
in bits, plus the conditional length of Pe and Pf (see Figure 4), or the number of bytes of the
burst-payload in bytes, plus the conditional length of Pe and Pf if exist.
The length-code indicates the number of bits, bytes or 8-bytes unit according to data-type
within the data-burst, from 0 to 65 535. The size of the Pa, Pb, Pc and Pd is not counted in
the value of the length-code. In other words, the length-code indicates the number of bits of
the burst-payload in bits, plus the conditional length of Pe and Pf (see Figure 4), or the
number of bytes of the burst-payload in bytes, plus the conditional length of Pe and Pf if it
exists, or the number of 8-bytes unit of the burst-payload in bytes, plus the conditional length
of Pe and Pf if it exists.
Pa Pb Pc Pd Burst_payload
Length of the burst_payload
IEC  1292/03
Figure 5 – Length of the burst-payload specified by Pd

– 16 – 61937-1  IEC:2007+A1:2011
6.2 Burst-payload
The format of the burst-payload is specified by means of the data-type in preamble Pc and is
used to convey the information content. The data-bursts of several data-types are specified
in IEC 61937-2.
6.3 Stuffing
Not all bits are occupied during the transfer of data-bursts (see Figure 2). In the case where
the audio data-burst contains a multiple of 16-bit, all IEC 60958 subframes used are
completely filled.
6.3.1 Stuffing within an IEC 60958 subframe
In the case where the audio data-burst does not contain a multiple of 16-bit, the bits of the
burst payload to be conveyed in the last 16-bit data word shall be MSB aligned, and the
remaining bits of that subframe are set to ‘0’ (stuffing).
6.3.2 Stuffing between data-bursts
An unoccupied space between two data-bursts shall be stuffed with 16-bit data words which
are set to all ‘0’s.
6.3.3 Burst spacing
The following feature allows equipment reliably to detect whether the IEC 60958 signal is
conveying PCM or non-linear PCM data without relying on bit 1 of the channel status (see
Annex A). Four IEC 60958 subframes which have the contents of time slots 12 to 27 all set to
‘0’ shall be inserted between every data-burst.
All these four ‘0’ subframes with Pa and Pb will behave as an extended 96-bit sync code. In
the case of PCM transmission, the false occurrence of the sync code will be extremely small.
When the interface is not in the idle state, this requirement is automatically fulfilled unless
there are sequences of data-bursts so tightly packed that there is never a sequence of all four
‘0’ subframes preceding any Pas.

Pa Pb Pc Pd Burst_payload ‘0’s ‘0’s ‘0’s ‘0’s Pa Pb Pc Pd Burst_payload
R R
Burst spacing
Data-burst
Data burst
IEC  1293/03
Figure 6 – Burst spacing
7 Format of data-bursts
Data-types are categorized into three classes: audio data-burst, pause data-burst and null
data-burst. The type of the burst-payload is indicated by the data-type, bits 0 to 4 of Pc.
Repetition periods apply to all data-types, except for the null data-type.
Data-types are categorized into three classes: audio data-burst, pause data-burst and null
data-burst. The type of the burst-payload is indicated by bits 0 to 4 fields of Pc. Repetition
periods apply to all data-types except for the null data-type.

61937-1  IEC:2007+A1:2011 – 17 –
In cases where the IEC 60958 interface is idle, i.e. it is not used to convey any data but is
anticipating transmission of the non-linear PCM audio bitstream, channel status bit 1 is kept
‘1’ (see Annex A). Null data-bursts may be transferred to assist some receivers (which do not
observe channel status bit 1) in switching from non-linear PCM mode to linear PCM mode
unexpectedly (see 7.3).
In cases where the interface is used to convey non-linear PCM audio bitstreams, the
bitstream is broken into discrete data-bursts and stuffing is necessary between the data-
bursts (see 6.3.2). If gaps occur within the bitstreams, these stream gaps are filled with bursts
of the pause data-type.
PCM/non-PCM
Format
PCM
Non-PCM
Idle
‘Idle’
?
Audio bitstream
Null
No
Audio data-burst
Gap
Gap
data
occurs
needed
?
?
Yes
‘Send pause data-burst and
‘Send audio data-burst’ Send null data-burst
set repetition time’
‘Set repetition time’ (optional)
or ‘idle’
Repeti-
Yes
tion time
finished?
No
Stuffing
IEC  1294/03
Figure 7 – Flow chart of transmission of a bitstream

– 18 – 61937-1  IEC:2007+A1:2011
7.1 Pause data-burst
Occasionally, “stream gaps” (which means small discontinuities of the bitstream) may occur
between two audio data-bursts of a non-linear PCM encoded audio due to switching between
bitstreams in a transmitter. When a stream gap exists in the encoded audio bitstream, an
audio gap will exist in the decoded audio signal. Pause data-bursts are intended to be used to
fill the stream gaps. As indicated in Figure 8, pause data-bursts (Ps) are located with the
repetition period of the pause data-burst. The reference point R of a pause data-burst is bit 0
of its Pa, and it follows immediately after the stuffing, which follows the previous audio data-
burst. (The length of the audio data-burst with stuffing is the repetition period of the audio
data-burst.) If an unoccupied space exists following a pause data-burst, it is stuffed with all
‘0’s (see 6.3.2).
Audio-data Audio-data Audio-data
Stuffing P Stuffing P Stuffing P Stuffing Stuffing
burst burst burst
R R R R R R
Repetition
period of
Pause
Repetition period of Repetition period of
pause
burst P
the audio data-burst the audio data-burst
Gap in between the data bursts
IEC  1295/03
Figure 8 – Bridging gaps in-between data-bursts with three pause data-bursts
Pause data-bursts convey information to the audio decoder that a stream gap exists. The
pause data-bursts may also (optionally) indicate either the actual length of the audio gap, or
that the non-linear PCM audio data stream has stopped. This information may be used by the
audio decoder to minimize (or conceal) the existence of the audio gap, or in the case where
the bitstream stops, to trigger a fade-out of the audio. A sequence of pause data-bursts can
also assist decoder synchronization prior to the beginning of a non-linear PCM audio
bitstream. A short sequence of pause data-bursts may be sent immediately preceding the
transmission of the first audio data-burst.
The pause data-burst shall be transferred with the same bitstream-number as the bitstream-
number of the audio data stream which contains the stream gap to be filled with the pause
data-bursts, or for which synchronization is being assisted. In the case where a main audio
service bitstream and one or more associated audio service bitstreams are interleaved on the
interface, the pause data-bursts shall have the same bit-stream-number as the main audio
service. The pause data-burst is only used to fill the stream gaps between data-bursts of the
main audio service bitstreams.
The pause data-burst contains the burst-preamble and a 32-bit payload. The first 16-bit of the
payload contains the audio gap-length parameter. The remaining bits are reserved and are all
set to ‘0’. The audio gap-length parameter is an optional indication of the actual audio gap
length. This is the length, measured in sampling periods of the audio, between the anticipated
reference point of the next audio burst (based on the repetition period for that data-type −
see Table 5), and the actual reference point of the next audio data-burst. In the case of audio
with normal sampling rate, this length is equal to the number of PCM audio samples which
would be missing in the decoded output signal (in the case of half sampling-rate audio, the
number of PCM audio samples in the audio gap will be twice the value indicated by the gap-
length parameter). For the data-types with Pa as reference point, this length is equal to the
length, measured in sampling periods of the audio, between the first bit of Pa of the first
pause data-burst and the first bit of Pa of the next audio data-burst. The inclusion of non-zero
values of gap-length is optional, data sources are not required to indicate the length of
the audio gap.
61937-1  IEC:2007+A1:2011 – 19 –
The detailed use of the pause data-burst is dependent on the data-type of the audio data-
burst. For example, it is recommended that stream gaps between AC-3 data-bursts be filled
with a sequence of very short pause bursts, while the repetition period of pause data-bursts
between the data-burst of an MPEG type is related to the algorithm. The gap-length
parameter of the first pause data-burst of the sequence may (optionally) be used to indicate
the length of the audio gap which will occur due to the stream gap. The pause data-bursts in
the sequence which follows the first pause data-burst typically do not have a gap-length
specified (gap-length = 0). It should be noted that for data-types which use Pa of the burst as
the reference point, it is not necessary to differentiate between stream gaps and audio gaps;
in this case both are of the same length.
A gap may be filled with one single sequence of pause data-bursts with a single indication of
audio gap-length. For example, a
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