IEC 61937-1:2021

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
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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
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.160.30 ISBN 978-2-8322-9429-1

– 2 – IEC 61937-1:2021 © IEC 2021
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

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

– 4 – IEC 61937-1:2021 © IEC 2021
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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6) All users should ensure that they have the latest edition of this publication.
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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 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.
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.
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 document using a
colour printer.
– 6 – IEC 61937-1:2021 © IEC 2021
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
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

– 8 – IEC 61937-1:2021 © IEC 2021
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.

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

– 10 – IEC 61937-1:2021 © IEC 2021
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).

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
– 12 – IEC 61937-1:2021 © IEC 2021
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, number of bytes or number of
8-byte units according to data-type

Table 4 – Bit map of burst-preambles
IEC 60958 time-
27        12
slot 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 In accordance with Table 5, burst-info values Pc, bit 15 = MSB
Pd Length-code, bit 15 = MSB
6.1.8 Burst-info
6.1.8.1 General
The 16-bit burst-info contains information about the data that is found in the data-burst.
Table 5 – Fields of burst-info
Bits of Pc Value Contents Remark
0 to 6 Data-type See IEC 61937-2
7 0 Error flag indicating a valid burst-payload
1 Error flag indicating that this burst-payload is not valid
8 to 12 Data-type-dependent info
13 to 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.

6.1.8.2 Data-type
The 7-bit data-type is defined in bits 0 to 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 the other parts of IEC 61937.

6.1.8.3 Extended data-type
6.1.8.3.1 General
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 (see Table 6, Table 7 and Table 8).

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, number of bytes or
number of 8-byte units according to
data-type
Pe (conditional) 16-bit Extended data-type Table 7
Pf (conditional) 16-bit Reserved for future use Table 8

6.1.8.3.2 Fields of Pe
Table 7 – Fields of Pe (extended data-type)
Bits of Pe Value Contents Remark
0 to 15 0 to 65 535 Extended data-type See IEC 61937-2

The allocation of extended data-types is defined in IEC 61937-2. The extended data-types
themselves are specified in the following parts of IEC 61937.
6.1.8.3.3 Fields of Pf
Table 8 – Fields of Pf
Bits of Pf value Contents
0 to 15 0 to 65 535 Reserved for future use

– 14 – IEC 61937-1:2021 © IEC 2021
6.1.8.4 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.
6.1.8.5 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).
6.1.8.6 Bitstream-number
The 3-bit bitstream-number indicates to which bitstream the data-burst belongs. Eight codes
(0 to 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 bitstream-
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 the 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 can change, but the bitstream-number is constant for a
bitstream. For example, the pause data-burst used to bridge a stream gap between the data-
burst of an audio type contains the same bitstream-number.
6.1.9 Length-code
The length-code indicates the number of bits, bytes or 8-byte units according to the 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 lengths of Pe and Pf (see Figure 4), or the
number of bytes of the burst-payload in bytes, plus the conditional lengths of Pe and Pf, if
they exist, or the number of 8-byte units of the burst-payload in bytes, plus the conditional
lengths of Pe and Pf if they exist.

Figure 5 – Length of the burst-payload specified by Pd
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
6.3.1 General
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 bits, all IEC 60958 subframes used are
completely filled.
6.3.2 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).
6.3.3 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.
6.3.4 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 that 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 Pa (see Figure 6).

Figure 6 – Burst spacing
7 Format of data-bursts
7.1 General
Data-types are categorized into three classes: audio data-burst, pause data-burst and null
data-burst. The type of the burst-payload is normally indicated by bits 0 to 6 and 8 to 12 fields
of Pc. Repetition periods apply to all data-types except for the null data-type.
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
as '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).
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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 6.3.3). If gaps occur within the bitstreams, these stream gaps are filled with bursts
of the pause data-type.
Figure 7 – Flow chart of transmission of a bitstream
7.2 Pause data-burst
Occasionally, stream gaps can occur between two audio data-bursts of a non-linear PCM
encoded audio owing 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 6.3.3).

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 indicate either the actual length of the audio gap, or that the non-
linear PCM audio data stream has stopped. This information can 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 can 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 (see Figure 9). 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 a 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.
The detailed use of the pause data-burst is dependent on the data-type of the audio data-
burst. The gap-length parameter of the first pause data-burst of the sequence may be used to
indicate the length of the audio gap that will occur owing to the stream gap. The pause data-
bursts in the sequence that follows the first pause data-burst typically do not have a gap-
length specified (gap-length = 0). For data-types that 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 stream gap resulting from an audio gap of 768 samples long
may be filled with one sequence of pause data-bursts with an indication of gap-length = 768 in
the first pause data-burst.
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If the data source does not have the information about the full audio gap length at the time the
stream gap begins, it may signal an initial value for gap-length. If the data source then
determines that the audio gap will be longer than the initial indication, another sequence of
pause data-bursts may be initiated (following the first sequence by the repetition period) with
another gap-length value to signal to the decoder that the audio gap is being extended. If the
gap is further extended, additional sequences may be initiated. For example, a stream gap
could be filled with a number of smaller sequences of pause data-bursts, with the first pause
data-burst in each sequence indicating the gap-length bridged by that sequence (for example,
one sequence with a gap-length of 256 samples, followed by a sequence with gap-length
of 512, together bridging a gap of 768 sample periods).
The information about the full length of the audio gap in the first pause data-burst will allow
the decoder the possibility to perform the best concealment.

Figure 9 – Data-burst format of the data-type pause
The length of a gap is adjusted to be concealed completely with a sequence of pause data-
bursts whose repetition periods are defined for each particular encoding system as indicated
in the other parts of IEC 61937 The repetition period of a pause data-burst gives the interval
between Pa of a pause-burst and Pa of the next pause-burst.
The data-type-dependent info for pause data-bursts is given in Table 9 and Table 10.
Table 9 – Values of data-type-dependent info of the pause data-burst
Bits of Pc Value Contents
8 to 12 0 General use
1 Stop, frame sequence discontinued
2 to 31 Reserved
NOTE 1 A pause data-burst with data-type-dependent info set to 'general use' is used to fill a gap or preceding
encoded audio bitstream.
NOTE 2 Transmitters can use the STOP value to indicate that the transmission of the current encoded audio
...