EN 61938:2013

SLOVENSKI STANDARD
01-november-2013
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Multimedia systems - Guide to the recommended characteristics of analogue interfaces
to achieve interoperability (IEC 61938:2013)
Multimedia Systeme - Leitfaden für empfohlene Charakteristiken analoger Schnittstellen
zur Erreichung von Kompatibilität (IEC 61938:2013)
Systèmes multimédia - Guide des caractéristiques recommandées des interfaces
analogiques permettant d'obtenir l'interopérabilité (CEI 61938:2013)
Ta slovenski standard je istoveten z: EN 61938:2013
ICS:
33.160.60 9HþSUHGVWDYQLPXOWLPHGLMVNL Multimedia systems and
VLVWHPLLQRSUHPD]D teleconferencing equipment
WHOHNRQIHUHQFH
35.200 Vmesniška in povezovalna Interface and interconnection
oprema equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 61938
NORME EUROPÉENNE
September 2013
EUROPÄISCHE NORM
ICS 33.160.01; 35.200 Supersedes EN 61938:1997

English version
Multimedia systems -
Guide to the recommended characteristics
of analogue interfaces to achieve interoperability
(IEC 61938:2013)
Systèmes multimédia -  Multimedia Systeme -
Guide des caractéristiques Leitfaden für empfohlene Charakteristiken
recommandées des interfaces analoger Schnittstellen zur Erreichung von
analogiques permettant d'obtenir Kompatibilität
l'interopérabilité (IEC 61938:2013)
(CEI 61938:2013)
This European Standard was approved by CENELEC on 2013-08-01. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the CEN-CENELEC Management Centre or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the CEN-CENELEC Management Centre has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus,
the Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany,
Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

CEN-CENELEC Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2013 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61938:2013 E
Foreword
The text of document 100/2130/FDIS, future edition 2 of IEC 61938, prepared by IEC/TC 100 "Audio,
video and multimedia systems and equipment" was submitted to the IEC-CENELEC parallel vote and
approved by CENELEC as EN 61938:2013.

The following dates are fixed:
(dop) 2014-05-01
• latest date by which the document has to be
implemented at national level by
publication of an identical national
standard or by endorsement
• latest date by which the national (dow) 2016-08-01
standards conflicting with the
document have to be withdrawn
This document supersedes EN 61938:1997.

– 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;
– 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.

Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such
patent rights.
Endorsement notice
The text of the International Standard IEC 61938:2013 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:

IEC 60027 Series NOTE Harmonised as EN 60027 Series (not modified).
IEC 61293:1994 NOTE Harmonised as EN 61293:1994 (not modified).

- 3 - EN 61938:2013
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

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.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year

IEC 60038 2009 IEC standard voltages EN 60038 2011
(mod)
IEC 60094-2 1994 Magnetic tape sound recording and EN 60094-2 1995
+ corr. March 1995 reproducing systems -
Part 2: Calibration tapes
IEC 60107-6 1989 Recommended methods of measurement HD 567.6 S1 1990
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 - EN 60130-9 2011
Part 9: Circular connectors for radio and
associated sound equipment
IEC 60268-1 1985 Sound system equipment - HD 483.1 S2 1989
1)
+ A1 1988 Part 1: General - -
+ A2 1988 - -
IEC 60268-3 2000 Sound system equipment - EN 60268-3 2000
2)
Part 3: Amplifiers + corr. January 2002

IEC 60268-5 2003 Sound system equipment - EN 60268-5 2003
+ A1 2007 Part 5: Loudspeakers + A1 2009

IEC 60268-7 2010 Sound system equipment - EN 60268-7 2011
Part 7: Headphones and earphones

IEC 60268-11 1987 Sound system equipment - HD 483.11 S3 1993
+ A1 1989 Part 11: Application of connectors for the - -
3)
+ A2 1991 interconnection of sound system - -
components
IEC 60268-12 1987 Sound system equipment - EN 60268-12 1995
4)
+ A1 1991 Part 12: Application of connectors for - -

+ A2 1994 broadcast and similar use + A2 1995

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)
1)
HD 483.1 S2 includes A1 to IEC 60268-1.
2)
EN 60268-3 is superseded by EN 60268-3:2013, which is based on IEC 60268-3:2013.
3)
HD 483.11 S3 includes A1 + A2 to IEC 60268-11.
4)
EN 60268-12 includes A1 to IEC 60268-12.

Publication Year Title EN/HD Year
IEC 60958 Series Digital audio interface EN 60958 Series

ITU-R BT.1700 2005 Characteristics of composite video signals - -
for conventional analogue television systems

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

– 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

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

– 4 – 61938 © IEC:2013
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

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
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.
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;

– 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.
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.

– 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.
61938 © IEC:2013 – 9 –
Low Voltage
0 , 5V rated level Power level
or RF level
9.1
Microphone
Pre-
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
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
– 10 – 61938 © IEC:2013
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.

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]

– 12 – 61938 © IEC:2013
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 impedance of a piece of equipment and related to a
maximum input signal limited by non-linearity
3.12
rated source impedance
internal impedance, stated by the manufacturer, of the source supplying the signal to the
piece of equipment
Note 1 to entry: Unless otherwise specified, the rated source impedance is assumed to be a constant pure
resistance.
Note 2 to entry: The manufacturer may also give the range of source impedances which he considers tolerable in
practice.
Note 3 to entry: Multiple values, or a range of values, may be specified, providing the corresponding rated
(distortion-limited) output voltages and/or powers are also stated.
3.13
input impedance
internal impedance measured between the input terminal and its corresponding return of
the piece of equipment
3.14
rated source e.m.f.
e.m.f. specified by the manufacturer which, when connected to the input terminals in series
with the rated source impedance, gives rated distortion-limited output voltage across the
rated load impedance at an appropriate setting of the controls
3.15
minimum source e.m.f. for rated output voltage
e.m.f. which, when connected to the input terminals in series with the rated source
impedance, gives rated output voltage across the rated load impedance with the volume
control(s), if any, set for maximum gain and the tone control(s), if any, set as specified
for rated conditions
3.16
rated load impedance
impedance, specified by the manufacturer, to which the output terminals are to be connected
for measuring purposes
Note 1 to entry: Unless otherwise specified by the manufacturer, the rated load impedance shall be assumed to
be a constant pure resistance.
Note 2 to entry: Multiple values, or a range of values, may be specified, provided the corresponding rated
(distortion-limited) output voltages and/or powers are also stated.

61938 © IEC:2013 – 13 –
3.17
output source impedance
internal impedance measured between the output terminal and its corresponding return
under specified conditions
3.18
rated output voltage
voltage specified by the manufacturer, measured across the rated load-impedance of a
piece of equipment
3.19
overload source e.m.f.
maximum source e.m.f. for which a piece of equipment, connected as for rated conditions
and with an appropriate setting of the volume control, can deliver an output voltage
10 dB below the rated distortion limited output voltage without exceeding the rated total
harmonic distortion
3.20
externally powered microphone
microphone containing internal active circuitry that obtains its operating power from an
external device to which it is connected
3.21
powered input
point on a device at which an externally powered microphone may be connected
Note 1 to entry: This is a terminal which serves as an input for signals from a microphone and also as an
output for power to the microphone.
4 General conditions
All voltages are r.m.s. voltages, unless otherwise indicated.
Impedances of audio circuits are valid in the frequency range of 20 Hz to 20 kHz,
unless otherwise indicated.
Tables containing tolerances indicate that the equipment should operate over the entire
range of possible values, but may not meet all of its specifications at the given limits.
5 Power supply
5.1 Alternating current (a.c.) power supply voltages and frequencies
For a.c. power supply voltages and frequencies, refer to IEC 60038.
For special applications, for example ships and aircraft, other voltages and/or frequencies
and the permissible tolerances are subject to agreement between manufacturers and users.
5.2 Direct current (d.c.) power supply voltages
DC power supply voltages and the permissible tolerances are given in Table 1. The
equipment should operate over the range of voltages given, but may not necessarily meet
all of its specifications at the given limits.

– 14 – 61938 © IEC:2013
Table 1 – Direct current (d.c.) power supply voltages and tolerances
Operating voltage/cell
Rated
Type of power supply
voltage/cell
V
Lower Normal
Upper limit
V
limit voltage
Primary batteries
– Alkali-manganese, zinc chloride-zinc 1,5 1,0 1,5 1,65
– Lithium (organic electrolyte) 3,0 2,0 3,0 3,7
Secondary batteries:
– Lead-acid, except vehicle batteries 2,0 1,8 2,0 2,2
– Lead-acid, vehicle batteries 2,0 1,8 2,4 2,6
– Nickel-cadmium 1,2 1,1 1,2 1,4

5.3 Power supply feed for microphones
Refer to to 9.3, 9.4, and 9.5.
6 Interconnections
6.1 Connections
6.1.1 General
Signal cables shall have the appropriate electrical characteristics to permit the transfer of
signals between the parts of a system without unacceptable impairment.
NOTE The degree of impairment which is unacceptable depends on the system specification and the need
to comply with other international standards, such as those concerning electromagnetic compatibility.
6.1.2 Characteristics of cables
6.1.2.1 General
The following characteristics of cables should be taken into account.
6.1.2.2 Resistance of the conductors
A resistance of less than one-hundredth of the load impedance is usually acceptable for
loudspeaker connections. For other applications, values of one-tenth are acceptable.
NOTE Long cables may therefore require conductors of a larger cross-sectional area than those of short cables.
6.1.2.3 Insulation resistance
An insulation resistance of 50 MΩ is usually acceptable.
6.1.2.4 Magnetic and electromagnetic interference susceptibility of interconnections
The use of untwisted pairs or single conductors with separate return paths is a common
source of magnetic and electromagnetic interference at both audio and radio frequencies,
especially for loudspeaker wiring, and should be avoided. A description of the methods of
avoiding such interference is given in Annex A.

61938 © IEC:2013 – 15 –
6.1.2.5 Reactance of conductors
The acceptable values vary too widely to give more than general guidance. The cable
should not appreciably affect the signal being carried. In the absence of particular
requirements, the inductive reactance of the cable should not cause more than 1 dB
change in response over the frequency range of interest. The capacitive reactance
between the two conductors of a signal-carrying pair, or a coaxial cable, in parallel with the
load impedance, should be greater than the rated load impedance, at the highest frequency
of interest.
While it is not recommended to use cables in which single conductors carry different audio
signals, the capacitive reactance between conductors in this case should exceed 1 000
times the load impedance at the highest frequency of interest.
6.1.2.6 Capacitance from conductor to screen
The acceptable value varies too widely to give more than general guidance. In the absence
of particular requirements, the capacitive reactance of a coaxial cable, in parallel with the
load impedance, should be greater than the rated load impedance. The capacitance between
each conductor of a balanced pair and its screen should be equal within 7,5 %. A closer
tolerance is desirable.
NOTE The 7,5 % tolerance, which can be achieved using normal cable manufacturing methods, ensures
preservation of adequate common mode rejection in balanced circuits (see Whitlock, JAES, 1995-06). The
electromagnetic interference rejection of such circuits is dependent on impedance balance.
6.1.2.7 Characteristic impedance
This is usually only important for high-frequency signals (such as digital signals in accordance
with IEC 60958).
6.1.2.8 Continuity of screening
In some applications, the screen is connected to contacts of connectors at both ends of the
cable. In other cases, the screen is connected at one end of the cable only. When the screen
of a balanced cable is interrupted, for example to prevent the flow of circulating currents, such
interruption should be at the receiving end of the signal path. The screen of a coaxial cable
should not be interrupted. Connections between equipment should comply with the
requirements of AES48.
The screening of signal cables and connectors shall not be used as a means for the
preservation of safety earth continuity for the prevention of electric shock hazard.
6.1.2.9 Efficiency of screening
The use of screening is meant to reduce the unwanted effects of electromagnetic
disturbances, such as:
a) in reducing crosstalk between conductors in the same cable;
b) in reducing emission of unwanted signals from the cable;
c) in maintaining immunity from external signals entering via the cable.
NOTE These characteristics are related, but good performance in one respect does not ensure good
performance in another.
6.2 Connectors
For connectors used within the system, refer to the International Standards cited in
Clause 2.
– 16 – 61938 © IEC:2013
7 Marking and symbols for marking
7.1 Marking
Terminals and controls shall be adequately marked to give information regarding their
function, characteristics and polarity.
The marking shall be such that it is possible to adjust the controls and to identify their
positions with sufficient accuracy in connection with the information given in the user
instructions.
7.2 Symbols for marking
Marking preferably should be composed of letter symbols, signs, numbers and colours,
which are internationally intelligible. Refer to IEC 60027, IEC 60417, IEC 60617 and
IEC 61293 for such symbols of marking.
Markings not included in the above-mentioned standards shall be clearly explained in the user
instructions.
8 Electrical recommended values
8.1 General purpose output/input
In order to preserve the maximum flexibility of use and compatibility in the design of
equipment, all inputs of destination equipment, and all outputs of source equipment for
general applications shall have the same specifications. These are termed "general purpose
input/output".
The manufacturer may choose to designate some or all of these input/outputs for particular
purposes. For example, the general purpose input/output for audio signal would be
designated for tuner, for tape recorder, or for auxiliary input, in order to simplify the operation,
but the specification of all such inputs and outputs nevertheless shall be identical.
8.2 General purpose audio output/input
8.2.1 Audio-only interfaces for consumer equipment
Table 2 gives the values for audio-only interfaces.
Table 2 – General purpose values for audio-only interfaces
a
Output Input
Recommended Recommended
values values
Output source impedance ≤2,2 kΩ Rated source impedance 2,2 kΩ
Rated load impedance 22 kΩ Input impedance ≥22 kΩ
b e
Rated output voltage 0,5 V Rated source e.m.f. 0,5 V
Minimum source e.m.f. for rated
c
Minimum output voltage 0,2 V 0,2 V
output voltage
d f
Maximum output voltage 2 V Overload source e.m.f. ≥2,8 V
a
The output voltages are measured with the rated load impedance connected.
b
The value corresponds to:
a) an aerial input level of 40 dB (pW) for FM radio tuners, i.e. 0,86
...