IEC 60958-1:2021

IEC 60958-1 ®
Edition 4.0 2021-09
REDLINE VERSION
INTERNATIONAL
STANDARD
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inside
Digital audio interface –
Part 1: General
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IEC 60958-1 ®
Edition 4.0 2021-09
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Digital audio interface –
Part 1: General
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.160.01 ISBN 978-2-8322-1023-9

– 2 – IEC 60958-1:2021 RLV © IEC 2021
CONTENTS
FOREWORD . 4
INTRODUCTION to Amendment 1 .
1 Scope . 7
2 Normative references. 7
3 Terms and definitions . 7
4 Interface format . 9
4.1 Structure of format . 9
4.1.1 Sub-frame format . 9
4.1.2 Frame format . 10
4.2 Channel coding . 11
4.3 Preambles . 11
4.4 Validity bit . 12
5 Channel status . 12
5.1 General . 12
5.2 Applications . 13
5.3 General assignment of the first and second channel status bits . 13
5.4 Category code . 13
6 User data . 15
6.1 General . 15
6.2 Applications . 15
6.2.1 Professional use . 15
6.2.2 Consumer use . 15
7 Electrical requirement . 15
7.1 Consumer application . 15
7.1.1 General . 15
7.1.2 Timing accuracy . 15
7.1.3 Unbalanced line . 16
7.2 Professional application . 19
8 Optical requirements . 19
8.1 Consumer application . 19
8.1.1 Optical specification Configuration of optical connection . 19
8.1.2 Optical connector . 19
8.2 Professional applications . 20
Annex A (informative) The use of the validity bit . 21
Annex B (informative) Application documents and specifications . 22
Annex C (informative) A relationship of the IEC 60958 series families . 23
Annex D (informative) Transmission of CD data other than linear PCM audio . 25
Annex E (informative) The IEC 60958 series conformant data format . 26
Annex F (informative) Stream change . 27
Annex G (informative) Characteristics of optical connection . 29
Bibliography . 31

Figure 1 – Sub-frame format (linear PCM application) . 10
Figure 2 – Frame format . 11

Figure 3 – Channel coding . 11
Figure 4 – Preamble M (shown as 11100010) . 12
Figure 5 – Simplified example of the configuration of the circuit (unbalanced) . 16
Figure 6 – Rise and fall times . 17
Figure 7 – Intrinsic jitter measurement filter . 17
Figure 8 – Eye diagram . 18
Figure 9 – Receiver jitter tolerance template . 18
Figure 10 – Basic optical connection . 19
Figure C.1 – Relationships of the IEC 60958 families . 23
Figure F.1 – Audio sources and AV receiver model . 27
Figure F.2 – Switching from linear PCM to non linear PCM . 28
Figure F.3 – Switching from non linear PCM to linear PCM . 28
Figure F.4 – Switching from non-linear PCM to non-linear PCM . 28

Table 1 – Preamble coding . 12
Table 2 – Channel status data format . 14
Table B.1 – Application documents and specifications . 22
Table C.1 – data_type values and application . 24
Table G.1 – Characteristics of standard optical connection (optical interface) . 29
Table G.2 – Characteristics of optical transmitter (optical interface) . 29
Table G.3 – Characteristics of optical receiver (optical interface) . 30
Table G.4 – Characteristics of fibre optic cable . 30
Table G.5 – Optical power budget for the link with plastic fibre . 30

– 4 – IEC 60958-1:2021 RLV © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DIGITAL AUDIO INTERFACE –
Part 1: General
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
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preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
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Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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rights. IEC shall not be held responsible for identifying any or all such patent rights.
This redline version of the official IEC Standard allows the user to identify the changes made to
the previous edition IEC 60958-1:2008+AMD1:2014 CSV. A vertical bar appears in the margin
wherever a change has been made. Additions are in green text, deletions are in strikethrough
red text.
IEC 60958-1 has been prepared by technical area 20: Analogue and digital audio, of IEC
technical committee 100: Audio, video and multimedia systems and equipment. It is an
International Standard.
This fourth edition cancels and replaces the third edition published in 2008, and
Amendment 1:2014. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) The relevant part of IEC 60958-5 is supported.
The text of this International Standard is based on the following documents:
Draft Report on voting
100/3544/CDV 100/3593/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
A list of all parts of the IEC 60958 series, under the general title Digital audio interface, can be
found on the IEC website.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
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The committee has decided that the contents of this document will remain unchanged until the
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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 60958-1:2021 RLV © IEC 2021
INTRODUCTION to Amendment 1
The revision of IEC 60958-1:2008 has become necessary in order to revise Annexes B and C,
and the Bibliography. Additional information for the use of the IEC 60958 conformant data
format has also been included.

DIGITAL AUDIO INTERFACE –
Part 1: General
1 Scope
This part of IEC 60958 describes a serial, uni-directional, self-clocking interface for the
interconnection of digital audio equipment for consumer and professional applications.
It provides the basic structure of the interface. Separate documents define items specific to
particular applications.
The interface is primarily intended to carry monophonic or stereophonic programmes, encoded
using linear PCM and with a resolution of up to 24 bits per sample.
When used for other purposes, the interface is able to carry audio data coded other than as
linear PCM coded audio samples. Provision is also made to allow the interface to carry data
related to computer software, multimedia technologies, or signals coded using non-linear PCM.
The format specification for these applications is not part of this document.
The interface is intended for operation at audio sampling frequencies of 32 kHz and above.
Auxiliary information is transmitted along with the programme.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60268-11:1987, Sound system equipment – Part 11: Application of connectors for the
interconnection of sound system components
IEC 60874-17, Connectors for optical fibres and cables – Part 17: Sectional specification for
fibre optic connector – Type F-05 (friction lock)
IEC 60958-3, Digital audio interface – Part 3: Consumer applications
IEC 60958-4 (all parts), Digital audio interface – Part 4: Professional applications
IEC 60958-5, Digital audio interface – Part 5: Consumer application enhancement
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

– 8 – IEC 60958-1:2021 RLV © IEC 2021
3.1
sampling frequency
frequency of the samples representing an audio signal
Note 1 to entry: When more than one signal is transmitted through the same interface, the sampling frequencies
are identical.
3.2
audio sample word
value of a digital audio sample; representation is linear in 2's complement binary form
Note 1 to entry: Positive numbers correspond to positive analogue voltages at the input of the analogue-to-digital
converter (ADC).
3.3
auxiliary sample bit
four least significant bits (LSBs) which can be assigned as auxiliary sample bits and used for
auxiliary information when the number of audio sample bits in the main data field is less than
or equal to 20
3.4
validity bit
bit indicating whether the main data field bits in the sub-frame (time slots 4 to 27 or 8 to 27,
depending on the audio word length as described in 4.1.1) are reliable or not
3.5
channel status
the channel status carries data carrying, in a fixed format, information associated with each
main data field channel which is decodable by any interface user
Note 1 to entry: Examples of information to be carried in the channel status are: length of audio sample words, pre-
emphasis, sampling frequency, time codes, alphanumeric source and destination codes.
3.6
user data
the user data channel is provided to carry any other information
3.7
parity bit
bit provided to permit the detection of an odd number of errors resulting from malfunctions in
the interface
3.8
preamble
specific patterns used for synchronization
Note 1 to entry: There are three different preambles (see 4.3).
3.9
sub-frame
fixed structure used to carry information (see 4.1.1 and 4.1.2)
3.10
frame
sequence of two successive and associated sub-frames
3.11
block
group of 192 consecutive frames

Note 1 to entry: The start of a block is designated by a special sub-frame preamble (see 4.3).
3.12
channel coding
coding method by which the binary digits are represented for transmission through the interface
3.13
unit interval (UI)
shortest nominal time interval in the coding scheme
Note 1 to entry: There are 128 UI in a sample frame.
3.14
interface jitter
deviation in the timing of interface data transitions (zero crossings) when compared with an
ideal clock
3.15
intrinsic jitter
output interface jitter of a device that is either free-running or is synchronized to a jitter-free
reference
3.16
jitter gain
ratio of the amplitude of jitter components at the output to their amplitude at the synchronization
input to the device under test
4 Interface format
4.1 Structure of format
4.1.1 Sub-frame format
Each sub-frame is divided into 32 time slots, numbered from 0 to 31 (see Figure 1).
Time slots 0 to 3 (preambles) carry one of the three permitted preambles (see 4.1.2 and 4.3;
also see Figure 2).
Time slots 4 to 27 (main data field) carry the audio sample word in linear 2's complement
representation. The most significant bit (MSB) is carried by time slot 27.
When a 24-bit coding range is used, the LSB is in time slot 4 (see Figure 1).
When a 20-bit coding range is used, time slots 8 to 27 carry the audio sample word with the LSB
in time slot 8. Time slots 4 to 7 may be used for other applications. Under these circumstances,
the bits in the time slots 4 to 7 are designated auxiliary sample bits (see Figure 1).
If the source provides fewer bits than the interface allows (either 20 or 24), the unused LSBs
are set to a logical "0".
For a non-linear PCM audio application or a data application the main data field may carry any
other information.
Time slot 28 (validity bit) carries the validity bit associated with the main data field (see 4.4).
Time slot 29 (user data bit) carries 1 bit of the user data channel associated with the main data
field channel transmitted in the same sub-frame. For the applications, refer to the other parts
of IEC 60958.
– 10 – IEC 60958-1:2021 RLV © IEC 2021
Time slot 30 (channel status bit) carries 1 bit of the channel status information associated with
the main data field channel transmitted in the same sub-frame. For details refer to the other
parts of IEC 60958.
Time slot 31 (parity bit) carries a parity bit such that time slots 4 to 31 inclusive carry an even
number of ones and an even number of zeroes (even parity).
NOTE The preambles have even parity as an explicit property.

Figure 1 – Sub-frame format (linear PCM application)
Annex E describes the IEC 60958 series conformant data format that utilises the sub-frame
format.
4.1.2 Frame format
A frame is uniquely composed of two sub-frames (see Figure 2). For linear coded audio
applications, the rate of transmission of frames normally corresponds exactly to the source
sampling frequency.
In 2-channel operation mode, the samples taken from both channels are transmitted by time
multiplexing in consecutive sub-frames. The first sub-frame (left or "A" channel in stereophonic
operation and primary channel in monophonic operation) normally starts with preamble "M".
However, the preamble changes to preamble "B" once every 192 frames to identify the start of
the block structure used to organize the channel status information. The second sub-frame
(right or "B" channel in stereophonic operation and secondary channel in monophonic operation)
always starts with preamble "W".
In single channel operation mode in a professional application, the frame format is the same as
in the 2-channel mode. Data is carried in the first sub-frame and may be duplicated in the
second sub-frame. If the second sub-frame is not carrying duplicate data, then time slot 28,
(validity flag) shall be set to logical "1".
NOTE For historical reasons preambles "B", "M" and "W" are, for use in professional applications, referred to as
"Z", "X" and "Y", respectively.
Annex C describes the relation of the IEC 60958 series families based on the frame format.

Figure 2 – Frame format
4.2 Channel coding
To minimize the direct current (d.c.) component on the transmission line, to facilitate clock
recovery from the data stream and to make the interface insensitive to the polarity of
connections, time slots 4 to 31 are encoded in biphase-mark.
Each bit to be transmitted is represented by a symbol comprising two consecutive binary states.
The first state of a symbol is always different from the second state of the previous symbol. The
second state of the symbol is identical to the first if the bit to be transmitted is logical "0".
However, it is different if the bit is logical "1" (see Figure 3).

Figure 3 – Channel coding
4.3 Preambles
Preambles are specific patterns providing synchronization and identification of the sub-frames
and blocks.
To achieve synchronization within one sampling period and to make this process completely
reliable, these patterns violate the biphase-mark code rules, thereby avoiding the possibility of
data imitating the preambles.
A set of three preambles is used. These preambles are transmitted in the time allocated to four
time slots at the start of each sub-frame (time slots 0 to 3), and are represented by eight
successive states. The first state of the preamble is always different from the second state of
the previous symbol (representing the parity bit). Depending on this state, the preambles are
as shown in Table 1.
– 12 – IEC 60958-1:2021 RLV © IEC 2021
Table 1 – Preamble coding
Preceding state 0 1
Preamble code Channel coding
"B" or "Z" 11101000 00010111 Sub-frame 1 and
(see note to 4.1.2) the start of the block
"M" or "X" 11100010 00011101 Sub-frame 1
"W" or "Y" 11100100 00011011 Sub-frame 2

Like biphase code, these preambles are d.c. free and provide clock recovery. They differ in at
least two states from any valid biphase sequence.
Figure 4 represents preamble "M".
NOTE Owing to the even-parity bit in time slot 31, all preambles start with a transition in the same direction
(see 4.1.1). Thus, only one of these sets of preambles is, in practice, transmitted through the interface. However, it
is necessary for both sets to be decodable because either polarity is possible in a connection.

Figure 4 – Preamble M (shown as 11100010)
4.4 Validity bit
The validity bit is logical "0" if the information in the main data field is reliable, and it is logical
"1" if it is not. There is no default state for the validity bit.
NOTE For transmissions not using a linear PCM coding, this bit may can be set. This is intended to prevent
accidental decoding of non-audio data to analogue before a complete channel status block is received. See Annex A.
5 Channel status
5.1 General
For every sub-frame, the channel status provides information related to the data carried in the
main data field of that same sub-frame.
Channel status information is organised in a 192-bit block, subdivided into 24 bytes. The first
bit of each block is carried in the frame with preamble "B". The channel status data format is
defined in Table 2.
The specific organisation depends on the application. In the descriptions, the suffix "0"
designates the first byte or bit. Where channel status bits are combined to form non-binary
values, the least significant bit should be transmitted first, unless otherwise indicated.

5.2 Applications
The primary application is indicated by the first channel status bit (bit 0) of a block as defined
in 5.3.
For professional applications, refer to IEC 60958-4.
For consumer applications, refer to IEC 60958-3 and IEC 60958-5.
Secondary applications may be defined within the framework of these primary applications.
Application documents or specifications are listed in Annex B.
5.3 General assignment of the first and second channel status bits
The first and second channel status bits (bit 0 and bit 1) are specified as follows.
Byte 0
Bit 0 "0" Consumer use of channel status block.
"1" Professional use of channel status block.

Bit 1 "0" Main data field represents linear PCM samples.
"1" Main data field used for other purposes.
Annex D describes an exception case of bit 1 status. Annex F describes a receiver's behaviour
when bit 1 is being altered.
5.4 Category code
Channel status including category code is defined in IEC 60958-3 for consumer applications;
these category codes are used for other variations of IEC 60958 for consumer use, such as
IEC 61937.
Also, channel status is defined in IEC 60958-4 for professional applications; these channel
statuses are used for other variations for professional use such as SMPTE 337M ST 337 and
others.
– 14 – IEC 60958-1:2021 RLV © IEC 2021
Table 2 – Channel status data format
Byte
0 a b
bit 0 1 2 3 4 5 6 7
bit 8 9 10 11 12 13 14 15
bit 16 17 18 19 20 21 22 23
bit 24 25 26 27 28 29 30 31
bit 32 33 34 35 36 37 38 39
bit 40 41 42 43 44 45 46 47
bit 48 49 50 51 52 53 54 55
bit 56 57 58 59 60 61 62 63
bit 64 65 66 67 68 69 70 71
bit 72 73 74 75 76 77 78 79
bit 80 81 82 83 84 85 86 87
bit 88 89 90 91 92 93 94 95
bit 96 97 98 99 100 101 102 103
bit 104 105 106 107 108 109 110 111
bit 112 113 114 115 116 117 118 119
bit 120 121 122 123 124 125 126 127
bit 128 129 130 131 132 133 134 135
bit 136 137 138 139 140 141 142 143
bit 144 145 146 147 148 149 150 151
bit 152 153 154 155 156 157 158 159
bit 160 161 162 163 164 165 166 167
bit 168 169 170 171 172 173 174 175
bit 176 177 178 179 180 181 182 183
bit 184 185 186 187 188 189 190 191

a: use of channel status block.

b: linear PCM identification.

6 User data
6.1 General
The default value of the user bits is logical "0".
6.2 Applications
6.2.1 Professional use
User data may be used in any way required by the user. Application details are described in
IEC 60958-4.
6.2.2 Consumer use
The application of the user data in digital audio equipment for consumer use is according to
rules described in IEC 60958-3 and IEC 60958-5.
7 Electrical requirement
7.1 Consumer application
7.1.1 General
Two types of transmission lines are defined: unbalanced line and optical fibre.
7.1.2 Timing accuracy
7.1.2.1 Accuracy of sampling frequency (clock accuracy)
7.1.2.1.1 General
Three levels of sampling frequency accuracy are defined to meet various requirements of the
frequency accuracy. These levels shall be indicated in the channel status data.
7.1.2.1.2 Level I: high-accuracy mode
−6
The transmitted sampling frequency shall be within a tolerance of ±50 × 10 .
7.1.2.1.3 Level II: normal-accuracy mode
−6
The transmitted sampling frequency shall be within a tolerance of ±1 000 × 10 .
7.1.2.1.4 Level III: variable pitch shifted clock mode
The signal in this mode can be received by specially designed receivers.
NOTE The frequency range is under consideration. A range of ±12,5 % is envisaged.
7.1.2.1.5 Interface frame rate not matched to sampling frequency
This state is used to indicate high speed and other transfers where the interface does not carry
an embedded sampling frequency clock.
7.1.2.2 Receiver locking range
By default, receivers should be able to lock to signals of level II accuracy with respect to the
supported standard sampling frequencies.

– 16 – IEC 60958-1:2021 RLV © IEC 2021
If a receiver is only capable of normal operation with a narrower locking range, then this range
should exceed the sample frequency tolerance of level I and it shall be specified as a level I
receiver.
If a receiver is capable of normal operation at sample rate variations corresponding to level III,
then this shall be specified as a level III receiver.
NOTE Until the range for level III has been defined, the frequency range supported by a level
III receiver should be at least ±12,5 %. For clarity, the actual value should be specified.
7.1.2.3 Receiver sampling frequency support
The product specification or application standard may define the sampling frequencies that shall
be supported by a receiver. In the absence of such a definition, the receiver shall support 32 kHz,
44,1 kHz and 48 kHz operation.
7.1.3 Unbalanced line
7.1.3.1 General characteristics
The interconnecting cable shall be unbalanced and screened (shielded) with a nominal
characteristic impedance of (75 ± 26,25) Ω at frequencies from 0,1 MHz to 128 times the
maximum frame rate.
The transmission circuit configuration shown in Figure 5 may be used.

Figure 5 – Simplified example of the configuration of the circuit (unbalanced)
NOTE For implementation, additional components may can be needed. A transformer in the transmitter with a
floating (non-earthed) secondary can be used to avoid any potential earth loops and provide a useful bandwidth
limitation to reduce high-frequency radiation.
7.1.3.2 Line driver characteristics
7.1.3.2.1 Output impedance
The line driver shall have an unbalanced output with an internal impedance of (75 ± 15) Ω, when
measured at the terminals to which the line is connected, at frequencies from 0,1 MHz to 128
times the maximum frame rate.
7.1.3.2.2 Signal amplitude
The signal amplitude shall be (0,5 ± 0,1) V peak-to-peak, when measured across a (75 ± 0,75) Ω
resistor connected to the output terminals, without any interconnecting cable present.

7.1.3.2.3 DC output voltage
The d.c. voltage shall be less than 0,05 V, when measured across a (75 ± 0,75) Ω resistor
connected to the output terminals, without any interconnecting cable present.
7.1.3.2.4 Rise and fall times
The time difference between the 10 % and 90 % points of any transition shall be less than 0,4 UI
(see Figure 6).
Figure 6 – Rise and fall times
7.1.3.2.5 Intrinsic jitter
The peak intrinsic output jitter measured at all the data transition zero crossings shall be less
than 0,05 UI when measured with the intrinsic jitter measurement filter.
NOTE This applies both when the equipment is locked to an effectively jitter-free timing reference (which may can
be a modulated digital audio signal) and when the equipment is free-running.
The jitter weighting filter is shown in Figure 7. It is a minimum-phase high pass filter with a 3 dB
frequency of 700 Hz, a first order roll-off to 70 Hz and with a passband gain of unity.

Figure 7 – Intrinsic jitter measurement filter
7.1.3.2.6 Jitter gain or peaking
The sinusoidal jitter gain from any timing reference input to the signal output shall be less than
3 dB at all frequencies.
– 18 – IEC 60958-1:2021 RLV © IEC 2021
7.1.3.3 Line receiver characteristics
7.1.3.3.1 Terminating impedance
The receiver shall present a substantially resistive impedance of (75 ± 3,75) Ω to the inter-
connecting cable over the frequency band 0,1 MHz to 128 times the maximum frame rate.
7.1.3.3.2 Maximum input signals
The receiver shall correctly interpret the data when presented with a signal whose peak-to-peak
voltage, measured in accordance with 7.1.3.2.2, is 0,6 V.
7.1.3.3.3 Minimum input signals
The receiver shall correctly sense the data when a random input signal produces the eye
of 200 mV and T of 0,5 UI (see Figure 8).
diagram characterized by a V
min min
NOTE This diagram does not define the tolerance to deviation in the zero crossings. These are defined by the jitter
tolerance template in 7.1.3.3.4, which requires that the minimum pulse width be not smaller than 0,8 UI.
Figure 8 – Eye diagram
7.1.3.3.4 Receiver jitter tolerance
An interface data receiver should correctly decode an incoming data stream with any sinusoidal
jitter defined by the jitter tolerance template of Figure 9.

Figure 9 – Receiver jitter tolerance template

NOTE The template requires a jitter tolerance of 0,2 UI peak-to-peak at frequencies above
400 kHz, 0,25 UI between 400 kHz and 200 Hz, increasing with the inverse of frequency below
200 Hz to level off at 10 UI peak-to-peak below 5 Hz.
7.1.3.4 Connectors
The standard connector for both outputs and inputs shall be the free pin connector and fixed
socket connector described in 8.6 of Table IV of IEC 60268-11:1987.
A male plug shall be used at both ends of the cable.
Equipment manufacturers shall clearly label digital audio inputs and outputs.
7.2 Professional application
Electrical requirements for professional applications are described in IEC 60958-4.
8 Optical requirements
8.1 Consumer application
8.1.1 Optical specification
8.1.1.1 Configuration of optical connection
The basic optical connection configuration is shown in Figure 10. The optical matching values
are described in Annex G; these values apply at the reference points 2 and 3.
The overall characteristics of a fibre optic cable plant are described in IEC 60793-2 and
IEC 60794-2 for fibre and cable, and in IEC 60874-1 for the connectors.
The reference points 1 and 4 apply to the electrical input and output of the electro-optical and
opto-electrical converter, respectively. Detailed specifications are provided only in relation to
optical reference points 2 and 3.

Figure 10 – Basic optical connection
In Figure 10, reference point 1 is the electrical input of the optical transmitter, reference point 2
is the optical interface between optical transmitter and FOCP, reference point 3 is the optical
interface between FOCP and optical receiver, and reference point 4 is the electrical output of
the optical receiver. "FOCP" means "fibre optic cable plant", which is the serial combination of
fibre optic cable sections, connectors and splices providing the optical path between two
terminal devices, between two optical devices or between terminal devices and an optical
device.
8.1.2 Optical connector
8.1.2.1 Circular type
Refer to JEITA EIAJ RC-5720BC (see Bibliography).

– 20 – IEC 60958-1:2021 RLV © IEC 2021
8.1.2.2 Rectangular type
Refer to IEC 60874-17 JEITA EIAJ RC-5720C (see Bibliography).
8.2 Professional applications
Optical requirements for professional applications are described in the IEC 60958-4 series.

Annex A
(informative)
The use of the validity bit
The IEC 60958 series is based on two different industry standards: the AES/EBU digital audio
interface standard (AES3 and EBU Tech. 3250-E) and the digital interface specification by Sony
and Philips (Sony-Philips Digital Interface Format (SPDIF)) introduced with the Compact Disc
Digital Audio system.
Unfortunately, significant differences between the two standards exist, which can contribute in part
to the different application areas: professional and consumer. The differences have contributed
to many misunderstandings about the use and compatibility of the standards.
Originally, the definition of validity was, in both industry standards, that it indicated whether or
not the associated audio sample was "secure and error free". Although, at first glance this may
can seem like a clear definition, in practice it has led to important practical problems. It is
unclear how the receiver should interpret this. When the sample is signalled not to be in error,
it is not clear whether the transmitter has performed a successful concealment. If a sample is
signalled in error, it is not clear whether the sample should be passed on unchanged, concealed,
or muted.
As a result, the AES has adopted in the 1992 revision of the AES3 standard a different wording:
Validity indicates "whether the audio sample bits are suitable for conversion to an analogue
audio signal".
Over the years, the application of the IEC 60958 series has gained popularity, resulting in a
growing number of products conforming to its provisions. With these in use, applications other
than strictly linear PCM audio transmission started to appear as well. The same basic frame
structure is used, but the information transferred in the "audio sample word" is not encoded as
linear PCM audio. As it is not always clearly indicated what kind of signal is carried, connection
of such a transmitter to a linear PCM receiver may can result in a very loud and noisy audio
signal.
Therefore, it has been proposed in the revision of IEC 60958 to also adopt the wording of the
AES3 standard for the validity bit definition. However, especially in consumer applications, the
transmitter often has no active control of the validity bit. In many cases, this is generated by
the error correction circuitry and automatically copied in the IEC 60958 bitstream. A change
of definition would, in theory, necessitate a redesign of circuits which have been in use for many
years.
For this reason, the definition of the validity bit remains basically unchanged in IEC 60958.
However, it is noted that for applications not using a linear PCM coding the bit may be set to "1",
in which case it can prevent accidental decoding of non-audio data to analogue before a
complete channel status block is received. For future applications of IEC 60958 with non-linear
PCM data, such a provision is highly recommended.
Additionally, in IEC 60958-4, it is specified that the validity bit shall be used to indicate whether
the audio sample is "suitable for conversion to an analogue audio signal using linear PCM
coding". This retains, for professional applications, the intention of the wording in the AES3
standard.
Although not a perfect solution to problems relating to the use of the validity bit, the definitions
as adopted in IEC 60958 seem to be the best achievable compromise to date.
The use described in this annex should be applied to all other IEC 60958 data conformant
formats. This applies, for example, to the IEC 60958 series conformant mode of IEC 61883-6.

– 22 – IEC 60958-1:2021 RLV © IEC 2021
Annex B
(informative)
Application documents and specifications
Table B.1 indicates application documents and specifications based on channel status bit 0 and
bit 1, as defined in 5.3.
Table B.1 – Application documents and specifications
Byte 0 of channel status
Specifications
Bit 0 Bit 1
0 0 IEC 60958-3 and IEC 60958-5
1 0 IEC 60958-4
0 1 IEC 61937, IEC 62105 and others
1 1 SMPTE ST 337 and others
For that part of the channel status that is n
...

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

– 2 – IEC 60958-1:2021 © IEC 2021
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Interface format . 8
4.1 Structure of format . 8
4.1.1 Sub-frame format . 8
4.1.2 Frame format . 9
4.2 Channel coding . 10
4.3 Preambles . 10
4.4 Validity bit . 11
5 Channel status . 11
5.1 General . 11
5.2 Applications . 11
5.3 General assignment of the first and second channel status bits . 11
5.4 Category code . 12
6 User data. 14
6.1 General . 14
6.2 Applications . 14
6.2.1 Professional use . 14
6.2.2 Consumer use . 14
7 Electrical requirement . 14
7.1 Consumer application . 14
7.1.1 General . 14
7.1.2 Timing accuracy . 14
7.1.3 Unbalanced line . 15
7.2 Professional application . 18
8 Optical requirements . 18
8.1 Consumer application . 18
8.1.1 Configuration of optical connection . 18
8.1.2 Optical connector. 18
8.2 Professional applications . 19
Annex A (informative) The use of the validity bit . 20
Annex B (informative) Application documents and specifications . 21
Annex C (informative) A relationship of the IEC 60958 series families . 22
Annex D (informative) Transmission of CD data other than linear PCM audio . 24
Annex E (informative) The IEC 60958 series conformant data format . 25
Annex F (informative) Stream change . 26
Annex G (informative) Characteristics of optical connection . 28
Bibliography . 30

Figure 1 – Sub-frame format (linear PCM application) . 9
Figure 2 – Frame format . 9
Figure 3 – Channel coding . 10

Figure 4 – Preamble M (shown as 11100010) . 11
Figure 5 – Simplified example of the configuration of the circuit (unbalanced) . 15
Figure 6 – Rise and fall times . 16
Figure 7 – Intrinsic jitter measurement filter . 16
Figure 8 – Eye diagram . 17
Figure 9 – Receiver jitter tolerance template . 17
Figure 10 – Basic optical connection . 18
Figure C.1 – Relationships of the IEC 60958 families . 22
Figure F.1 – Audio sources and AV receiver model . 26
Figure F.2 – Switching from linear PCM to non linear PCM . 26
Figure F.3 – Switching from non linear PCM to linear PCM . 27
Figure F.4 – Switching from non-linear PCM to non-linear PCM . 27

Table 1 – Preamble coding . 10
Table 2 – Channel status data format . 13
Table B.1 – Application documents and specifications . 21
Table C.1 – data_type values and application . 23
Table G.1 – Characteristics of standard optical connection (optical interface) . 28
Table G.2 – Characteristics of optical transmitter (optical interface) . 28
Table G.3 – Characteristics of optical receiver (optical interface) . 29
Table G.4 – Characteristics of fibre optic cable . 29
Table G.5 – Optical power budget for the link with plastic fibre . 29

– 4 – IEC 60958-1:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DIGITAL AUDIO INTERFACE –
Part 1: General
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC 60958-1 has been prepared by technical area 20: Analogue and digital audio, of IEC
technical committee 100: Audio, video and multimedia systems and equipment. It is an
International Standard.
This fourth edition cancels and replaces the third edition published in 2008, and
Amendment 1:2014. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) The relevant part of IEC 60958-5 is supported.

The text of this International Standard is based on the following documents:
Draft Report on voting
100/3544/CDV 100/3593/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
A list of all parts of the IEC 60958 series, under the general title Digital audio interface, can be
found on the IEC website.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – IEC 60958-1:2021 © IEC 2021
DIGITAL AUDIO INTERFACE –
Part 1: General
1 Scope
This part of IEC 60958 describes a serial, uni-directional, self-clocking interface for the
interconnection of digital audio equipment for consumer and professional applications.
It provides the basic structure of the interface. Separate documents define items specific to
particular applications.
The interface is primarily intended to carry monophonic or stereophonic programmes, encoded
using linear PCM and with a resolution of up to 24 bits per sample.
When used for other purposes, the interface is able to carry audio data coded other than as
linear PCM coded audio samples. Provision is also made to allow the interface to carry data
related to computer software, multimedia technologies, or signals coded using non-linear PCM.
The format specification for these applications is not part of this document.
The interface is intended for operation at audio sampling frequencies of 32 kHz and above.
Auxiliary information is transmitted along with the programme.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60268-11:1987, Sound system equipment – Part 11: Application of connectors for the
interconnection of sound system components
IEC 60958-3, Digital audio interface – Part 3: Consumer applications
IEC 60958-4 (all parts), Digital audio interface – Part 4: Professional applications
IEC 60958-5, Digital audio interface – Part 5: Consumer application enhancement
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
sampling frequency
frequency of the samples representing an audio signal

Note 1 to entry: When more than one signal is transmitted through the same interface, the sampling frequencies
are identical.
3.2
audio sample word
value of a digital audio sample; representation is linear in 2's complement binary form
Note 1 to entry: Positive numbers correspond to positive analogue voltages at the input of the analogue-to-digital
converter (ADC).
3.3
auxiliary sample bit
four least significant bits (LSBs) which can be assigned as auxiliary sample bits and used for
auxiliary information when the number of audio sample bits in the main data field is less than
or equal to 20
3.4
validity bit
bit indicating whether the main data field bits in the sub-frame (time slots 4 to 27 or 8 to 27,
depending on the audio word length as described in 4.1.1) are reliable or not
3.5
channel status
data carrying, in a fixed format, information associated with each main data field channel which
is decodable by any interface user
Note 1 to entry: Examples of information to be carried in the channel status are: length of audio sample words, pre-
emphasis, sampling frequency, time codes, alphanumeric source and destination codes.
3.6
user data
data provided to carry any other information
3.7
parity bit
bit provided to permit the detection of an odd number of errors resulting from malfunctions in
the interface
3.8
preamble
specific patterns used for synchronization
Note 1 to entry: There are three different preambles (see 4.3).
3.9
sub-frame
fixed structure used to carry information (see 4.1.1 and 4.1.2)
3.10
frame
sequence of two successive and associated sub-frames
3.11
block
group of 192 consecutive frames
Note 1 to entry: The start of a block is designated by a special sub-frame preamble (see 4.3).
3.12
channel coding
coding method by which the binary digits are represented for transmission through the interface

– 8 – IEC 60958-1:2021 © IEC 2021
3.13
unit interval (UI)
shortest nominal time interval in the coding scheme
Note 1 to entry: There are 128 UI in a sample frame.
3.14
interface jitter
deviation in the timing of interface data transitions (zero crossings) when compared with an
ideal clock
3.15
intrinsic jitter
output interface jitter of a device that is either free-running or is synchronized to a jitter-free
reference
3.16
jitter gain
ratio of the amplitude of jitter components at the output to their amplitude at the synchronization
input to the device under test
4 Interface format
4.1 Structure of format
4.1.1 Sub-frame format
Each sub-frame is divided into 32 time slots, numbered from 0 to 31 (see Figure 1).
Time slots 0 to 3 (preambles) carry one of the three permitted preambles (see 4.1.2 and 4.3;
also see Figure 2).
Time slots 4 to 27 (main data field) carry the audio sample word in linear 2's complement
representation. The most significant bit (MSB) is carried by time slot 27.
When a 24-bit coding range is used, the LSB is in time slot 4 (see Figure 1).
When a 20-bit coding range is used, time slots 8 to 27 carry the audio sample word with the LSB
in time slot 8. Time slots 4 to 7 may be used for other applications. Under these circumstances,
the bits in the time slots 4 to 7 are designated auxiliary sample bits (see Figure 1).
If the source provides fewer bits than the interface allows (either 20 or 24), the unused LSBs
are set to a logical "0".
For a non-linear PCM audio application or a data application the main data field may carry any
other information.
Time slot 28 (validity bit) carries the validity bit associated with the main data field (see 4.4).
Time slot 29 (user data bit) carries 1 bit of the user data channel associated with the main data
field channel transmitted in the same sub-frame. For the applications, refer to the other parts
of IEC 60958.
Time slot 30 (channel status bit) carries 1 bit of the channel status information associated with
the main data field channel transmitted in the same sub-frame. For details refer to the other
parts of IEC 60958.
Time slot 31 (parity bit) carries a parity bit such that time slots 4 to 31 inclusive carry an even
number of ones and an even number of zeroes (even parity).
NOTE The preambles have even parity as an explicit property.

Figure 1 – Sub-frame format (linear PCM application)
Annex E describes the IEC 60958 series conformant data format that utilises the sub-frame
format.
4.1.2 Frame format
A frame is uniquely composed of two sub-frames (see Figure 2). For linear coded audio
applications, the rate of transmission of frames normally corresponds exactly to the source
sampling frequency.
In 2-channel operation mode, the samples taken from both channels are transmitted by time
multiplexing in consecutive sub-frames. The first sub-frame (left or "A" channel in stereophonic
operation and primary channel in monophonic operation) normally starts with preamble "M".
However, the preamble changes to preamble "B" once every 192 frames to identify the start of
the block structure used to organize the channel status information. The second sub-frame
(right or "B" channel in stereophonic operation and secondary channel in monophonic operation)
always starts with preamble "W".
In single channel operation mode in a professional application, the frame format is the same as
in the 2-channel mode. Data is carried in the first sub-frame and may be duplicated in the
second sub-frame. If the second sub-frame is not carrying duplicate data, then time slot 28,
(validity flag) shall be set to logical "1".
NOTE For historical reasons preambles "B", "M" and "W" are, for use in professional applications, referred to as
"Z", "X" and "Y", respectively.
Annex C describes the relation of the IEC 60958 series families based on the frame format.

Figure 2 – Frame format
– 10 – IEC 60958-1:2021 © IEC 2021
4.2 Channel coding
To minimize the direct current (d.c.) component on the transmission line, to facilitate clock
recovery from the data stream and to make the interface insensitive to the polarity of
connections, time slots 4 to 31 are encoded in biphase-mark.
Each bit to be transmitted is represented by a symbol comprising two consecutive binary states.
The first state of a symbol is always different from the second state of the previous symbol. The
second state of the symbol is identical to the first if the bit to be transmitted is logical "0".
However, it is different if the bit is logical "1" (see Figure 3).

Figure 3 – Channel coding
4.3 Preambles
Preambles are specific patterns providing synchronization and identification of the sub-frames
and blocks.
To achieve synchronization within one sampling period and to make this process completely
reliable, these patterns violate the biphase-mark code rules, thereby avoiding the possibility of
data imitating the preambles.
A set of three preambles is used. These preambles are transmitted in the time allocated to four
time slots at the start of each sub-frame (time slots 0 to 3), and are represented by eight
successive states. The first state of the preamble is always different from the second state of
the previous symbol (representing the parity bit). Depending on this state, the preambles are
as shown in Table 1.
Table 1 – Preamble coding
Preceding state 0 1
Preamble code Channel coding
"B" or "Z" 11101000 00010111 Sub-frame 1 and
(see note to 4.1.2) the start of the block
"M" or "X" 11100010 00011101 Sub-frame 1
"W" or "Y" 11100100 00011011 Sub-frame 2

Like biphase code, these preambles are d.c. free and provide clock recovery. They differ in at
least two states from any valid biphase sequence.
Figure 4 represents preamble "M".
NOTE Owing to the even-parity bit in time slot 31, all preambles start with a transition in the same direction
(see 4.1.1). Thus, only one of these sets of preambles is, in practice, transmitted through the interface. However, it
is necessary for both sets to be decodable because either polarity is possible in a connection.

Figure 4 – Preamble M (shown as 11100010)
4.4 Validity bit
The validity bit is logical "0" if the information in the main data field is reliable, and it is logical
"1" if it is not. There is no default state for the validity bit.
NOTE For transmissions not using a linear PCM coding, this bit can be set. This is intended to prevent accidental
decoding of non-audio data to analogue before a complete channel status block is received. See Annex A.
5 Channel status
5.1 General
For every sub-frame, the channel status provides information related to the data carried in the
main data field of that same sub-frame.
Channel status information is organised in a 192-bit block, subdivided into 24 bytes. The first
bit of each block is carried in the frame with preamble "B". The channel status data format is
defined in Table 2.
The specific organisation depends on the application. In the descriptions, the suffix "0"
designates the first byte or bit. Where channel status bits are combined to form non-binary
values, the least significant bit should be transmitted first, unless otherwise indicated.
5.2 Applications
The primary application is indicated by the first channel status bit (bit 0) of a block as defined
in 5.3.
For professional applications, refer to IEC 60958-4.
For consumer applications, refer to IEC 60958-3 and IEC 60958-5.
Secondary applications may be defined within the framework of these primary applications.
Application documents or specifications are listed in Annex B.
5.3 General assignment of the first and second channel status bits
The first and second channel status bits (bit 0 and bit 1) are specified as follows.
Byte 0
Bit 0 "0" Consumer use of channel status block.

– 12 – IEC 60958-1:2021 © IEC 2021
"1" Professional use of channel status block.

Bit 1 "0" Main data field represents linear PCM samples.
"1" Main data field used for other purposes.
Annex D describes an exception case of bit 1 status. Annex F describes a receiver's behaviour
when bit 1 is being altered.
5.4 Category code
Channel status including category code is defined in IEC 60958-3 for consumer applications;
these category codes are used for other variations of IEC 60958 for consumer use, such as
IEC 61937.
Also, channel status is defined in IEC 60958-4 for professional applications; these channel
statuses are used for other variations for professional use such as SMPTE ST 337 and others.

Table 2 – Channel status data format
Byte
0 a b
bit 0 1 2 3 4 5 6 7
bit 8 9 10 11 12 13 14 15
bit 16 17 18 19 20 21 22 23
bit 24 25 26 27 28 29 30 31
bit 32 33 34 35 36 37 38 39
bit 40 41 42 43 44 45 46 47
bit 48 49 50 51 52 53 54 55
bit 56 57 58 59 60 61 62 63
bit 64 65 66 67 68 69 70 71
bit 72 73 74 75 76 77 78 79
bit 80 81 82 83 84 85 86 87
bit 88 89 90 91 92 93 94 95
bit 96 97 98 99 100 101 102 103
bit 104 105 106 107 108 109 110 111
bit 112 113 114 115 116 117 118 119
bit 120 121 122 123 124 125 126 127
bit 128 129 130 131 132 133 134 135
bit 136 137 138 139 140 141 142 143
bit 144 145 146 147 148 149 150 151
bit 152 153 154 155 156 157 158 159
bit 160 161 162 163 164 165 166 167
bit 168 169 170 171 172 173 174 175
bit 176 177 178 179 180 181 182 183
bit 184 185 186 187 188 189 190 191

a: use of channel status block.

b: linear PCM identification.

– 14 – IEC 60958-1:2021 © IEC 2021
6 User data
6.1 General
The default value of the user bits is logical "0".
6.2 Applications
6.2.1 Professional use
User data may be used in any way required by the user. Application details are described in
IEC 60958-4.
6.2.2 Consumer use
The application of the user data in digital audio equipment for consumer use is according to
rules described in IEC 60958-3 and IEC 60958-5.
7 Electrical requirement
7.1 Consumer application
7.1.1 General
Two types of transmission lines are defined: unbalanced line and optical fibre.
7.1.2 Timing accuracy
7.1.2.1 Accuracy of sampling frequency (clock accuracy)
7.1.2.1.1 General
Three levels of sampling frequency accuracy are defined to meet various requirements of the
frequency accuracy. These levels shall be indicated in the channel status data.
7.1.2.1.2 Level I: high-accuracy mode
−6
The transmitted sampling frequency shall be within a tolerance of ±50 × 10 .
7.1.2.1.3 Level II: normal-accuracy mode
−6
The transmitted sampling frequency shall be within a tolerance of ±1 000 × 10 .
7.1.2.1.4 Level III: variable pitch shifted clock mode
The signal in this mode can be received by specially designed receivers.
NOTE The frequency range is under consideration. A range of ±12,5 % is envisaged.
7.1.2.1.5 Interface frame rate not matched to sampling frequency
This state is used to indicate high speed and other transfers where the interface does not carry
an embedded sampling frequency clock.
7.1.2.2 Receiver locking range
By default, receivers should be able to lock to signals of level II accuracy with respect to the
supported standard sampling frequencies.

If a receiver is only capable of normal operation with a narrower locking range, then this range
should exceed the sample frequency tolerance of level I and it shall be specified as a level I
receiver.
If a receiver is capable of normal operation at sample rate variations corresponding to level III,
then this shall be specified as a level III receiver.
Until the range for level III has been defined, the frequency range supported by a level III
receiver should be at least ±12,5 %. For clarity, the actual value should be specified.
7.1.2.3 Receiver sampling frequency support
The product specification or application standard may define the sampling frequencies that shall
be supported by a receiver. In the absence of such a definition, the receiver shall support 32 kHz,
44,1 kHz and 48 kHz operation.
7.1.3 Unbalanced line
7.1.3.1 General characteristics
The interconnecting cable shall be unbalanced and screened (shielded) with a nominal
characteristic impedance of (75 ± 26,25) Ω at frequencies from 0,1 MHz to 128 times the
maximum frame rate.
The transmission circuit configuration shown in Figure 5 may be used.

Figure 5 – Simplified example of the configuration of the circuit (unbalanced)
NOTE For implementation, additional components can be needed. A transformer in the transmitter with a floating
(non-earthed) secondary can be used to avoid any potential earth loops and provide a useful bandwidth limitation to
reduce high-frequency radiation.
7.1.3.2 Line driver characteristics
7.1.3.2.1 Output impedance
The line driver shall have an unbalanced output with an internal impedance of (75 ± 15) Ω, when
measured at the terminals to which the line is connected, at frequencies from 0,1 MHz to 128
times the maximum frame rate.
7.1.3.2.2 Signal amplitude
The signal amplitude shall be (0,5 ± 0,1) V peak-to-peak, when measured across a (75 ± 0,75) Ω
resistor connected to the output terminals, without any interconnecting cable present.

– 16 – IEC 60958-1:2021 © IEC 2021
7.1.3.2.3 DC output voltage
The d.c. voltage shall be less than 0,05 V, when measured across a (75 ± 0,75) Ω resistor
connected to the output terminals, without any interconnecting cable present.
7.1.3.2.4 Rise and fall times
The time difference between the 10 % and 90 % points of any transition shall be less than 0,4 UI
(see Figure 6).
Figure 6 – Rise and fall times
7.1.3.2.5 Intrinsic jitter
The peak intrinsic output jitter measured at all the data transition zero crossings shall be less
than 0,05 UI when measured with the intrinsic jitter measurement filter.
NOTE This applies both when the equipment is locked to an effectively jitter-free timing reference (which can be a
modulated digital audio signal) and when the equipment is free-running.
The jitter weighting filter is shown in Figure 7. It is a minimum-phase high pass filter with a 3 dB
frequency of 700 Hz, a first order roll-off to 70 Hz and with a passband gain of unity.

Figure 7 – Intrinsic jitter measurement filter
7.1.3.2.6 Jitter gain or peaking
The sinusoidal jitter gain from any timing reference input to the signal output shall be less than
3 dB at all frequencies.
7.1.3.3 Line receiver characteristics
7.1.3.3.1 Terminating impedance
The receiver shall present a substantially resistive impedance of (75 ± 3,75) Ω to the inter-
connecting cable over the frequency band 0,1 MHz to 128 times the maximum frame rate.
7.1.3.3.2 Maximum input signals
The receiver shall correctly interpret the data when presented with a signal whose peak-to-peak
voltage, measured in accordance with 7.1.3.2.2, is 0,6 V.
7.1.3.3.3 Minimum input signals
The receiver shall correctly sense the data when a random input signal produces the eye
diagram characterized by a V of 200 mV and T of 0,5 UI (see Figure 8).
min min
NOTE This diagram does not define the tolerance to deviation in the zero crossings. These are defined by the jitter
tolerance template in 7.1.3.3.4, which requires that the minimum pulse width be not smaller than 0,8 UI.
Figure 8 – Eye diagram
7.1.3.3.4 Receiver jitter tolerance
An interface data receiver should correctly decode an incoming data stream with any sinusoidal
jitter defined by the jitter tolerance template of Figure 9.

Figure 9 – Receiver jitter tolerance template

– 18 – IEC 60958-1:2021 © IEC 2021
The template requires a jitter tolerance of 0,2 UI peak-to-peak at frequencies above 400 kHz,
0,25 UI between 400 kHz and 200 Hz, increasing with the inverse of frequency below 200 Hz
to level off at 10 UI peak-to-peak below 5 Hz.
7.1.3.4 Connectors
The standard connector for both outputs and inputs shall be the free pin connector and fixed
socket connector described in 8.6 of Table IV of IEC 60268-11:1987.
A male plug shall be used at both ends of the cable.
Equipment manufacturers shall clearly label digital audio inputs and outputs.
7.2 Professional application
Electrical requirements for professional applications are described in IEC 60958-4.
8 Optical requirements
8.1 Consumer application
8.1.1 Configuration of optical connection
The basic optical connection configuration is shown in Figure 10. The optical matching values
are described in Annex G; these values apply at the reference points 2 and 3.
The overall characteristics of a fibre optic cable plant are described in IEC 60793-2 and
IEC 60794-2 for fibre and cable, and in IEC 60874-1 for the connectors.
The reference points 1 and 4 apply to the electrical input and output of the electro-optical and
opto-electrical converter, respectively. Detailed specifications are provided only in relation to
optical reference points 2 and 3.

Figure 10 – Basic optical connection
In Figure 10, reference point 1 is the electrical input of the optical transmitter, reference point 2
is the optical interface between optical transmitter and FOCP, reference point 3 is the optical
interface between FOCP and optical receiver, and reference point 4 is the electrical output of
the optical receiver. "FOCP" means "fibre optic cable plant", which is the serial combination of
fibre optic cable sections, connectors and splices providing the optical path between two
terminal devices, between two optical devices or between terminal devices and an optical
device.
8.1.2 Optical connector
8.1.2.1 Circular type
Refer to JEITA EIAJ RC-5720C (see Bibliography).

8.1.2.2 Rectangular type
Refer to JEITA EIAJ RC-5720C (see Bibliography).
8.2 Professional applications
Optical requirements for professional applications are described in the IEC 60958-4 series.

– 20 – IEC 60958-1:2021 © IEC 2021
Annex A
(informative)
The use of the validity bit
The IEC 60958 series is based on two different industry standards: the AES/EBU digital audio
interface standard (AES3 and EBU Tech. 3250-E) and the digital interface specification by Sony
and Philips (Sony-Philips Digital Interface Format (SPDIF)) introduced with the Compact Disc
Digital Audio system.
Unfortunately, significant differences between the two standards exist, which can contribute in part
to the different application areas: professional and consumer. The differences have contributed
to many misunderstandings about the use and compatibility of the standards.
Originally, the definition of validity was, in both industry standards, that it indicated whether or
not the associated audio sample was "secure and error free". Although, at first glance this can
seem like a clear definition, in practice it has led to important practical problems. It is unclear
how the receiver should interpret this. When the sample is signalled not to be in error, it is not
clear whether the transmitter has performed a successful concealment. If a sample is signalled
in error, it is not clear whether the sample should be passed on unchanged, concealed, or
muted.
As a result, the AES has adopted in the 1992 revision of the AES3 standard a different wording:
Validity indicates "whether the audio sample bits are suitable for conversion to an analogue
audio signal".
Over the years, the application of the IEC 60958 series has gained popularity, resulting in a
growing number of products conforming to its provisions. With these in use, applications other
than strictly linear PCM audio transmission started to appear as well. The same basic frame
structure is used, but the information transferred in the "audio sample word" is not encoded as
linear PCM audio. As it is not always clearly indicated what kind of signal is carried, connection
of such a transmitter to a linear PCM receiver can result in a very loud and noisy audio signal.
Therefore, it has been proposed in the revision of IEC 60958 to also adopt the wording of the
AES3 standard for the validity bit definition. However, especially in consumer applications, the
transmitter often has no active control of the validity bit. In many cases, this is generated by
the error correction circuitry and automatically copied in the IEC 60958 bitstream. A change
of definition would, in theory, necessitate a redesign of circuits which have been in use for many
years.
For this reason, the definition of the validity bit remains basically unchanged in IEC 60958.
However, it is noted that for applications not using a linear PCM coding the bit may be set to "1",
in which case it can prevent accidental decoding of non-audio data to analogue before a
complete channel status block is received. For future
...