IEC 61938:2013

Multimedia systems - Guide to the recommended characteristics of analogue interfaces to achieve interoperability

IEC 61938:2013 gives guidance on current practice for the characteristics of multimedia analogue interfaces to achieve interoperability between equipment from different manufacturers. It is not a performance standard. This second edition cancels and replaces the first edition published in 1996 and constitutes a technical revision. It includes the following significant technical changes:
- the values in each table were chosen with respect to the state of the art and representative of best practice in industry;
- plug-in power systems and soundcard power systems are added;
- a new subclause 12.3 has been created: Interoperability of portable audio headphones/earphones and portable audio equipment;
- a new Annex A describing pairing and screening of conductors is added;
- a new Annex B describing phantom power variants for specialized applications is also added.

Systèmes multimédia - Guide des caractéristiques recommandées des interfaces analogiques permettant d'obtenir l'interopérabilité

La CEI 61938:2013 donne des directives relatives à la pratique courante en ce qui concerne les caractéristiques des interfaces analogiques multimédia permettant d'obtenir l'interopérabilité entre des matériels provenant de fabricants différents. Il ne s'agit pas d'une norme de performance. Cette deuxième édition annule et remplace la première édition parue en 1996 et constitue une révision technique. Elle inclut les modifications techniques suivantes:
- les valeurs de chaque tableau ont été choisies en tenant compte de l'état de l'art représentatif de la meilleure pratique en industrie;
- un système d'alimentation enfichable et un système d'alimentation de carte son ont été ajoutés;
- un nouveau paragraphe 12.3 a été créé: Interopérabilité des casques audio/écouteurs portables et matériels audio portables;
- une nouvelle Annexe A décrivant l'appariement et le blindage des conducteurs a été ajoutée;
- une nouvelle Annexe B décrivant les variantes d'alimentation fantôme pour applications spécialisées a également été ajoutée.

General Information

• Status: Published
• Publication Date: 26-Jun-2013
• ICS: 33.160.01 - Audio, video and audiovisual systems in general
• ICS: 35.200 - Interface and interconnection equipment
• Technical Committee: TC 100 - Audio, video and multimedia systems and equipment
• Drafting Committee: MT 61938 - TC 100/MT 61938
• Current Stage: DELPUB - Deleted Publication
• Completion Date: 12-Jan-2018

Relations

• Revised: IEC 61938:2018 - Multimedia systems - Guide to the recommended characteristics of analogue interfaces to achieve interoperability (GMT)
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 61938


®


Edition 2.0 2013-06



INTERNATIONAL



STANDARD



NORME
INTERNATIONALE


Multimedia systems – Guide to the recommended characteristics of analogue
interfaces to achieve interoperability

Systèmes multimédia – Guide des caractéristiques recommandées des
interfaces analogiques permettant d'obtenir l'interopérabilité


IEC 61938:2013

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IEC 61938



®



Edition 2.0 2013-06







INTERNATIONAL





STANDARD







NORME



INTERNATIONALE











Multimedia systems – Guide to the recommended characteristics of analogue

interfaces to achieve interoperability




Systèmes multimédia – Guide des caractéristiques recommandées des

interfaces analogiques permettant d'obtenir l'interopérabilité

















INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

ELECTROTECHNIQUE

PRICE CODE
INTERNATIONALE

CODE PRIX W


ICS 33.160.60; 35.200 ISBN 978-2-83220-836-6



Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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– 2 – 61938 © IEC:2013


CONTENTS



FOREWORD . 5

INTRODUCTION . 7

1 Scope . 8


2 Normative references . 10

3 Terms and definitions . 10

4 General conditions. 13


5 Power supply . 13
5.1 Alternating current (a.c.) power supply voltages and frequencies . 13
5.2 Direct current (d.c.) power supply voltages . 13
5.3 Power supply feed for microphones . 14
6 Interconnections . 14
6.1 Connections . 14
6.1.1 General . 14
6.1.2 Characteristics of cables . 14
6.2 Connectors . 15
7 Marking and symbols for marking . 16
7.1 Marking . 16
7.2 Symbols for marking . 16
8 Electrical recommended values . 16
8.1 General purpose output/input . 16
8.2 General purpose audio output/input . 16
8.2.1 Audio-only interfaces for consumer equipment . 16
8.2.2 Interfaces for professional equipment and consumer equipment
where audio and video signals are present on the same connector or
cable . 18
8.3 General purpose video input/output . 19
9 Interoperability of microphones and amplifiers . 19
9.1 Microphones (excluding piezoelectric types) . 19
9.2 Power supply feed for electret microphones fed over a signal conductor
(“plug-in power”) . 20
9.3 Power supply feed for electret microphones fed by a separate conductor
(“soundcard power” or “PC power”) . 21

9.4 Phantom supply system . 21
9.4.1 General . 21
9.4.2 Supply voltage polarity . 22
9.4.3 Circuit diagram . 22
9.4.4 Value of the supply voltage . 22
9.4.5 Supply current . 22
9.4.6 Marking . 22
9.5 A-B supply system . 23
9.5.1 General . 23
9.5.2 Output impedance of the microphone . 23
9.5.3 Circuit diagram . 23
9.5.4 Connection of the power supply to earth . 23
9.5.5 Marking . 23
9.6 Polarity of the audio frequency voltage . 23

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61938 © IEC:2013 – 3 –


10 Interoperability of record-playing units (pick-ups) and amplifiers . 26

11 Interoperability of loudspeakers and amplifiers . 26


11.1 Single unit loudspeakers . 26

11.2 Loudspeaker systems . 26

11.2.1 Loudspeakers with built-in amplifier . 26

11.2.2 Impedance-defined loudspeaker systems . 27

11.2.3 Constant voltage loudspeaker systems . 27

11.3 Voltage (or power) interoperability of amplifiers and loudspeakers . 27


11.3.1 Overview . 27

11.3.2 Interoperability requirements . 28
11.4 Polarity of the sound pressure . 28
12 Interoperability of headphones and amplifiers . 28
12.1 General . 28
12.2 Interoperability of headphones with stationary amplifiers . 28
12.3 Interoperability of portable audio headphones/earphones and portable audio
equipment . 29
12.3.1 General . 29
12.3.2 Portable audio headphones/earphones . 29
12.3.3 Portable audio equipment . 29
12.3.4 Recommended values and input/output values for portable audio
headphones/earphones and portable audio equipment . 29
13 Interoperability of amplifiers with other amplifiers . 30
13.1 Pre-amplifiers and power amplifiers for general purpose and sound
reinforcement . 30
13.2 Broadcast and similar line amplifiers . 31
Annex A (informative) Pairing and screening of conductors . 32
Annex B (informative) Phantom power variants for specialized applications . 33
Bibliography . 34

Figure 1 – Audio and video sources and destinations . 9
Figure 2 – Example of plug-in power system for a single microphone . 24
Figure 3 – Example of plug-in power system for a two-channel microphone . 24
Figure 4 – Example of soundcard power system . 24
Figure 5 – Example of phantom power supply system . 25

Figure 6 – Example of A-B power supply system . 25

Table 1 – Direct current (d.c.) power supply voltages and tolerances . 14
Table 2 – General purpose values for audio-only interfaces . 16
Table 3 – General purpose values for audio signals for professional interfaces . 18
Table 4 – General purpose recommended values for video signals . 19
Table 5 – Recommended values for microphones and amplifiers . 20
Table 6 – Required values for phantom supply systems . 25
Table 7 – Required values for A-B power supply systems . 25
Table 8 – Recommended values for analogue record-playing units and amplifiers. 26
Table 9 – Recommended values for impedance-defined loudspeaker systems . 27
Table 10 – Recommended values for constant voltage loudspeaker systems . 27

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Table 11 – Recommended values for headphones and amplifiers in stationary

applications . 29

Table 12 – Recommended values for portable audio headphones/earphones and

portable audio equipment . 30


Table 13 – Recommended values for pre-amplifiers and power amplifiers . 31

Table 14 – Recommended values for broadcast and similar line amplifiers . 31

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61938 © IEC:2013 – 5 –


INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________



MULTIMEDIA SYSTEMS –

GUIDE TO THE RECOMMENDED CHARACTERISTICS

OF ANALOGUE INTERFACES TO ACHIEVE INTEROPERABILITY





FOREWORD


1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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.
International Standard IEC 61938 has been prepared by IEC technical committee 100: Audio,

video and multimedia systems and equipment.
This second edition cancels and replaces the first edition published in 1996 and constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– the main title was changed to: Multimedia systems – Guide to the recommended
characteristics of analogue interfaces to achieve interoperability;
– the scope was adapted to the title;
– a new introduction has been added. The necessity of the above revisions is mentioned in
this introduction;
– the values in each table were chosen with respect to the state of the art and
representative of best practice in industry;

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– 6 – 61938 © IEC:2013


– plug-in power systems and soundcard power systems are added;

– a new subclause12.3 has been created: Interoperability of portable audio headphones /

earphones and portable audio equipment;


– a new Annex A describing pairing and screening of conductors is added;

– a new Annex B describing phantom power variants for specialized applications is also

added.


The text of this standard is based on the following documents:


FDIS Report on voting

100/2130/FDIS 100/2155/RVD

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

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61938 © IEC:2013 – 7 –


INTRODUCTION


The first edition of IEC 61938 was derived from IEC 60268-15, IEC 60574-4 and IEC 60933-1

and also from related proposals which had been submitted up until the date of this revision.

IEC 60268-15 was the first standard to address 'interoperability' – the ability of equipment

from different manufacturers to be assembled into a system with full compatibility at every

'interface'. However, the purpose, terminology and implications of IEC 61938 are now widely

misunderstood because the words 'matching' and 'preferred' used in IEC 61938, are

frequently misinterpreted, resulting in IEC 61938 being regarded as a performance standard,

which was never its intention. The aim of this revision is to make the intention of this standard

easily comprehensible by using widely used terminology in the title and text of the standard.

The features of the revision are the following.
a) Unification and arrangement of existing related standards, including effective proposals
which have been submitted.
b) The concept of "general purpose input/output".
NOTE The standard numbers mentioned above correspond to the revised numbers, if applicable.

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– 8 – 61938 © IEC:2013


MULTIMEDIA SYSTEMS –

GUIDE TO THE RECOMMENDED CHARACTERISTICS

OF ANALOGUE INTERFACES TO ACHIEVE INTEROPERABILITY







1 Scope


This International Standard gives guidance on current practice for the characteristics of

multimedia analogue interfaces to achieve interoperability between equipment from different
manufacturers. It is not a performance standard.
Recommendations for interfaces for equipment used in vehicles, and for analogue video
interfaces for broadcast and similar equipment, are not given.
Refer to IEC 60958 for the interconnection of digital signals.
Figure 1 shows in a diagram the possible interfaces of the audio and video sources and
destinations.

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61938 © IEC:2013 – 9 –






Low Voltage
0 , 5V rated level Power level
or RF level

9.1


Microphone

Pre-
10
amplifier
Record player

High/low sensitivity




12/1 GHz Digital satellite 12.2
Headphones
converter radio tuner


8.2
Active
12/1 GHz Satellite TV tuner
13.1
8.3
loudspeaker
converter Analogue or digital

boxes
8.2
Terrestrial TV tuner
8.3
13.1
Audio power
Analogue or digital

amplifier
Auxiliary
11

8.2
AM/FM radio tuner loudspeaker
boxes
8.3
Video camera or
8.3
camcorder
Video monitor
8.2

Video tape recorder
8.3

8.2
Audio tape cassette
recorder analogue
9.1
Digital audio tape
8.2
Microphone recorder :DAT,DCC,

Minidisc,.
CD writeable recorder

8.2
CD/CD-i/CD-ROM
Laservision player

Auxiliary

Still picture camera
System Printer

Control
bus Personal/home

computer

12.3
Portable audio Portable audio

equipment headphones / earphones

Remote
Equaliser or
Digital sound Digital video processor
control
reverberation unit
processor and memory
emitter
(analogue)

IEC  1298/13

NOTE The numbers indicated above the arrows refer to the appropriate clause or subclauses of this standard.
Figure 1 – Audio and video sources and destinations
Low Voltage sources
Real time signal sources
Peripheral equipment
or pre-recorded signals
Real time signal sources
Radio or TV broadcast
Switchbox/source selector

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2 Normative references


The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any

amendments) applies.


IEC 60038:2009, IEC standard voltages


IEC 60094-2:1994, Magnetic tape recording and reproducing systems – Part 2: Calibration

tapes
IEC 60107-6:1989, Recommended methods of measurement on receivers for television
broadcast transmissions – Part 6: Measurements under conditions different from broadcast
signal standards
IEC 60130-9:2011, Connectors for frequencies below 3 MHz – Part 9: Circular connectors
for radio and associated sound equipment
IEC 60268-1:1985, Sound system equipment – Part 1: General
Amendment 1:1988
Amendment 2:1988
IEC 60268-3:2000, Sound system equipment – Part 3: Amplifiers
IEC 60268-5:2003, Sound system equipment – Part 5: Loudspeakers
Amendment 1:2007
IEC 60268-7:2010, Sound system equipment – Part 7: Headphones and earphones
IEC 60268-11:1987, Sound system equipment – Part 11: Application of connectors for the
interconnection of sound system components
Amendment 1:1989
Amendment 2:1991
IEC 60268-12:1987, Sound system equipment – Part 12: Application of connectors for
broadcast and similar use
Amendment 1:1991
Amendment 2:1994

IEC 60603-11:1992, Connectors for frequencies below 3 MHz for use with printed boards –
Part 11: Detail specification for concentric connectors (dimensions for free connectors and
fixed connectors)
IEC 60958 (all parts), Digital audio interface
ITU-R BT.1700:2005, Characteristics of composite video signals for conventional analogue
television systems
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

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61938 © IEC:2013 – 11 –


3.1

luminance signal

electrical signal representing the luminance of the television picture elements


[SOURCE: IEC 60050-723:1997, 723-05-56, modified, Note has been deleted]


3.2

chrominance signal

electrical signal that is associated with the luminance signal to convey colour information; in
practice this signal is made up of two components


[SOURCE: IEC 60050-723:1997, 723-05-57]

3.3
Y" signal
VBS signal
combined signal consisting of
– a luminance signal;
– blanking and synchronizing signals
Note 1 to entry: The Y" signal is the composite video signal (CVBS signal) without the C" signal.
3.4
colour signal
C" signal
chrominance signal with burst signal included, modulated on a subcarrier
3.5
composite video signal
CVS signal
combined signal consisting of
– a luminance signal;
– a colour signal
3.6
composite video, blanking and synchronization signal
CVBS signal
combined signal consisting of
– a luminance signal;
– a colour signal;

– blanking and synchronizing signals
3.7
blanking signal
signal used to control the suppression of the signal conveying picture information during
certain parts of the scanning period, for example, during fly-back
[SOURCE: IEC 60050:1997, 723-05-37, modified, Example has been deleted]
3.8
synchronizing signal
signal used to determine the timing for the scanning processes in transmission and reception
[SOURCE: IEC 60050:1997, 723-05-36]

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3.9

interface

shared boundary between two pieces of equipment, defined by functional characteristics,

common physical interconnection characteristics, signal characteristics and other

characteristics, as appropriate

[SOURCE: ISO/IEC 2382-9:1995, definition 09.01.06, modified, definition has been adapted]



3.10
minimum output voltage

voltage measured across the rated load impedance of a piece of equipment, and related to

a minimum input signal limited by signal to noise ratio

3.11
maximum output voltage
voltage measured across the rated load imp
...