SIST EN IEC 61938:2019

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Multimedia Systeme - Leitfaden für empfohlene Charakteristika analoger Schnittstellen zur Erreichung von KompatibilitätSystèmes multimédia - Guide des caractéristiques recommandées des interfaces analogiques permettant d'obtenir l'interopérabilitéMultimedia systems - Guide to the recommended characteristics of analogue interfaces to achieve interoperability (GMT)35.200Vmesniška in povezovalna opremaInterface and interconnection equipment33.160.60WHOHNRQIHUHQFHMultimedia systems and teleconferencing equipmentICS:Ta slovenski standard je istoveten z:EN IEC 61938:2018SIST EN 61938:2019en,fr,de01-april-2019SIST EN 61938:2019SLOVENSKI
STANDARDSIST EN 61938:20131DGRPHãþD

SIST EN 61938:2019
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN IEC 61938
March 2018 ICS 33.160.01; 35.200
Supersedes
EN 61938:2013
English Version
Multimedia systems - Guide to the recommended characteristics of analogue interfaces to achieve interoperability (IEC 61938:2018)
Systèmes multimédia - Guide des caractéristiques recommandées des interfaces analogiques permettant d'obtenir l'interopérabilité (IEC 61938:2018)
Multimedia Systeme - Leitfaden für empfohlene Charakteristika analoger Schnittstellen zur Erreichung von Kompatibilität (IEC 61938:2018) This European Standard was approved by CENELEC on 2018-02-16. 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, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung CEN-CENELEC Management Centre: Rue de la Science 23,
B-1040 Brussels © 2018 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61938:2018 E SIST EN 61938:2019

This document supersedes EN 61938:2013.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Endorsement notice The text of the International Standard IEC 61938:2018 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 Harmonized as EN 60027 (series). IEC 60130-9 NOTE Harmonized as EN 60130-9. IEC 61293:1994 NOTE Harmonized as EN 61293:1994 (not modified). IEC 62368-1:2014 NOTE Harmonized as EN 62368-1:2014 (modified). SIST EN 61938:2019

3 Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1
Where an International Publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies.
NOTE 2
Up-to-date information on the latest versions of the European Standards listed in this annex is available here: www.cenelec.eu.
Publication Year Title EN/HD Year IEC 60038 -
IEC standard voltages EN 60038 -
IEC 60094-2 -
Magnetic tape sound recording and reproducing systems - Part 2: Calibration tapes EN 60094-2 -
IEC 60268-1 -
Sound system equipment - Part 1: General HD 483.1 S2 -
IEC 60268-3 -
Sound system equipment - Part 3: Amplifiers EN 60268-3 -
IEC 60268-5 -
Sound system equipment - Part 5: Loudspeakers EN 60268-5 -
IEC 60268-7 2010
Sound system equipment - Part 7: Headphones and earphones EN 60268-7 2011
IEC 60268-11 1987
Sound system equipment - Part 11: Application of connectors for the interconnection of sound system components HD 483.11 S1 1990 + A1 1989
HD 483.11 S2 1991
+ A2 1991
HD 483.11 S3 1993
IEC 60268-12 -
Sound system equipment - Part 12: Application of connectors for broadcast and similar use EN 60268-12 -
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 series
Digital audio interface
EN 60958 series
ITU-R BT.1700 2005 Characteristics of composite video signals for conventional analogue television systems - -
SIST EN 61938:2019
SIST EN 61938:2019
IEC 61938 Edition 3.0 2018-01 INTERNATIONAL STANDARD
Multimedia systems –
Guide to the recommended characteristics of analogue interfaces to achieve interoperability
INTERNATIONAL ELECTROTECHNICAL COMMISSION
ICS 33.160.01, 35.200
ISBN 978-2-8322-5056-3
– 2 – IEC 61938:2018 © IEC 2018 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 (AC) power supply voltages and frequencies . 13 5.2 Direct current (DC) power supply voltages . 14 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 . 16 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 . 17 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 . 21 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 10 Interoperability of record-playing units (pick-ups) and amplifiers . 25 SIST EN 61938:2019

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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 . 26 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 . 27 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 . 23 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 . 24 Figure 6 – Example of A-B power supply system . 25 Figure B.1 – Caution symbol . 33
Table 1 – Direct current (DC) 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 . 25 Table 9 – Recommended values for impedance-defined loudspeaker systems . 26 Table 10 – Recommended values for constant voltage loudspeaker systems . 27 SIST EN 61938:2019

– 4 – IEC 61938:2018 © IEC 2018 Table 11 – Recommended values for headphones and amplifiers in stationary applications . 28 Table 12 – Recommended values for portable audio headphones/earphones and portable audio equipment . 29 Table 13 – Recommended values for pre-amplifiers and power amplifiers . 31 Table 14 – Recommended values for broadcast and similar line amplifiers . 31
SIST EN 61938:2019
IEC 61938:2018 © IEC 2018 – 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 third edition cancels and replaces the second edition published in 2013. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition: a) electric tolerance is standardized; b) recommended value of output source impedance is adjusted; c) value of 6 Ω is additionally recommended to impedance-defined loudspeaker systems; d) values in each table are chosen with respect to the state of the art and representative of best practice in industry.
SIST EN 61938:2019
– 6 – IEC 61938:2018 © IEC 2018 The text of this International Standard is based on the following documents: CDV Report on voting 100/2879/CDV 100/2996/RVC
Full information on the voting for the approval of this International Standard can be found in the report on voting indicated in the above table. This document has been drafted in accordance with the ISO/IEC Directives, Part 2. The committee has decided that the contents of this document will remain unchanged until the stability date indicated on the IEC website under "http://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. A bilingual version of this publication may be issued at a later date.
SIST EN 61938:2019
IEC 61938:2018 © IEC 2018 – 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'. The aim of the previous revision was to make the intention of this document easily comprehensible by using widely used terminology in the title and text of the document. The purpose of this revision is to expand the measurement frequency range in step with the progress of recent equipment. The features of the revision are the following: a) unification and arrangement of existing related standards, including effective proposals which have been submitted; b) extension of the measurement frequency range. NOTE The standard numbers mentioned above correspond to the revised numbers, if applicable.
SIST EN 61938:2019
– 8 – IEC 61938:2018 © IEC 2018 MULTIMEDIA SYSTEMS –
GUIDE TO THE RECOMMENDED CHARACTERISTICS
OF ANALOGUE INTERFACES TO ACHIEVE INTEROPERABILITY
1 Scope This document 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. SIST EN 61938:2019

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NOTE The numbers indicated above the arrows refer to the appropriate clause or subclauses of this document. Figure 1 – Audio and video sources and destinations IEC Low voltage or RF level 0,5 V rated level
Power level
Microphone Record player High/low sensitivity 9.1
Pre- amplifier Low voltage source
13.1
Headphones
Digital satellite radio tuner 12/1 GHz converter 12/1 GHz converter 12.2
13.1
Active loudspeaker boxes
Satellite TV tuner analogue or digital 8.2
8.3
8.3
8.2
Terrestrial TV tuner analogue or digital Audio power amplifier Auxiliary
8.2
AM/FM radio tuner
Real time signal sources Radio or TV broadcast 11
Loudspeaker boxes
Video monitor 8.3
8.3
Video camera or camcorder
8.2
Video tape recorder Audio tape cassette recorder analogue 8.3
8.2
Digital audio tape recorder: DAT, DCC, Minidisc, … 8.2
Microphone 9.1
Switchbox/source selector
CD writeable recorder 8.2
CD/CD-i/CD-ROM SACD DVD BD Laservision player Printer Auxiliary USB-DAC System control bus Real time signal sources or pre-recorder signals Remote control emitter Peripheral equipment Still picture camera Personal/home computer OTT 12.3
Portable audio equipment Portable audio headphones/earphones Equaliser or reverberation unit (analogue) Digital sound processor Digital video processor and memory SIST EN 61938:2019

– 10 – IEC 61938:2018 © IEC 2018 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 60038, IEC standard voltages IEC 60094-2, Magnetic tape recording and reproducing systems – Part 2: Calibration tapes IEC 60268-1, Sound system equipment – Part 1: General
IEC 60268-3, Sound system equipment – Part 3: Amplifiers IEC 60268-5, Sound system equipment – Part 5: Loudspeakers
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 IEC 60268-11:1987/AMD1:1989, Sound system equipment – Part 11: Application of connectors for the interconnection of sound system components IEC 60268-11:1987/AMD2:1991, Sound system equipment – Part 11: Application of connectors for the interconnection of sound system components IEC 60268-12, Sound system equipment – Part 12: Application of connectors for broadcast and similar use 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 60958:2016, Digital audio interface – ALL PARTS 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. 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
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.] SIST EN 61938:2019

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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 60050-723:1997, 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 60050-723:1997, 723-05-36] 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 SIST EN 61938:2019

– 12 – IEC 61938:2018 © IEC 2018 [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. that, 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. 3.17
output source impedance internal impedance measured between the output terminal and its corresponding return under specified conditions SIST EN 61938:2019

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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. 3.22
P12 designation of a specific phantom power supply system 3.23
P24 designation of a specific phantom power supply system 3.24
P48 designation of a specific phantom power supply system 4 General conditions All voltages are RMS voltages, unless otherwise indicated. Impedances of audio circuits are valid in the frequency range of 20 Hz to 20 kHz, unless otherwise indicated. Electrical tolerance is ±5 %, 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 (AC) power supply voltages and frequencies For AC 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. SIST EN 61938:2019

– 14 – IEC 61938:2018 © IEC 2018 5.2 Direct current (DC) 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. Table 1 – Direct current (DC) power supply voltages and tolerances Type of power supply Rated voltage/cell
V Operating voltage/cell V Lower limit Normal voltage Upper limit Primary batteries – Alkali-manganese, zinc chloride-zinc – Lithium (organic electrolyte)
1,5 3,0
1,0 2,0
1,5 3,0
1,65 3,7 Secondary batteries: – Lead-acid, except vehicle batteries –
Lead-acid, vehicle batteries – Nickel-cadmium
2,0 2,0 1,2
1,8 1,8 1,1
2,0 2,4 1,2
2,2 2,6 1,4
5.3 Power supply feed for microphones Refer 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. 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. SIST EN 61938:2019

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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. 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. SIST EN 61938:2019

– 16 – IEC 61938:2018 © IEC 2018 6.2 Connectors For connectors used within the system, refer to the International Standards cited in Clause 2. 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 Output a Input
Recommended values
Recommended values Output source impedance ≤2,2 kΩ Rated source impedance 2,2 kΩ Rated load impedance 22 kΩ Input impedance ≥22 kΩ Rated output voltage 0,5 V b Rated source e.m.f. 0,5 V e Minimum output voltage 0,2 V c Minimum source e.m.f. for rated output voltage 0,2 V Maximum output voltage 2 V d Overload source e.m.f. ≥2,8 V f Specifications of values of impedance may be extended to cover the frequency range 2 Hz to 200 kHz, if SIST EN 61938:2019

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required. 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 mV across 75 Ω or 1,73 mV across 300 Ω. The modulation factor is 54 %;
– an aerial input e.m.f. of 1 mV for AM radio tuners. The modulation factor is 30 %;
– a vision carrier input level of 70 dB (µV) for TV sound tuners, having the sound to vision carrier ratio of the relevant television system (see ITU-R BT.1700). The modulation factor is 54 % for both AM and FM.
The modulation factor of the above signals is based on the average modulation factor of the relevant emissions, averaged over at least 15 s;
b) the output of a tape player or monitor, when reproducing a calibration tape in accordance with IEC 60094-2;
c) the output of a digital audio source (see footnote to table g), when reproducing a sinewave signal recorded at a level 12 dB below "full scale" (see footnote to table d, item c) recorded digital signal;
d) a source level equal to the average level of the system in other cases. c The value corresponds to:
a) a level of 8 dB below the recording level given in footnote to table b, item b) above, in the case of a tape player or monitor;
b) the minimum source e.m.f. to the input of the system (8 dB below the rated source e.m.f.) in other cases.
The value as shown is not specified for tuners.
In the case of a digital audio source (see footnote to table g), it is not necessary to define a minimum output voltage since it is directly related to the rated output voltage. d The value corresponds to:
a) the maximum r.f. input signal level and maximum modulation in the case of tuners. In some countries, FM emissions may exceed the rated maximum system deviation, while in others this is not permitted. AM emissions employing high-efficiency modulation techniques may produce at the receiver an audio output voltage corresponding to an apparent modulation of more than 100 %, up to approximately 150 %;
b) the maximum recording level in the case of a tape player or monitor;
c) the "full scale" level, which is the sinewave signal having positive and negative peak values represented by the digital values of 7FFFH and 8001H in a 16-bit system in the case of a digital audio source (see footnote to table g). In the compact disc specification, these values correspond to a maximum (RMS) analogue output voltage of 2 V ± 3 dB;
d) the input of the system when applying the overload source e.m.f. (12 dB above the rated source e.m.f.) in other cases. e In the case of a tape recorder, the value which produces the same intensity of the magnetic field as that of the calibration tape in accordance with IEC 60094-2. f For inputs intended only for the connection of analogue sources, the value is greater than or equal to 2,0 V. For inputs intended for the connection of analogue outputs of digital audio sources (see footnote to table g), the value is greater than or equal to 2,8 V. g The digital audio source may be a compact disc (CD) player, a digital audio tape (DAT/DCC) recorder or player, a television receiver with digital sound reception facilities or a receiver for digital audio broadcast (see footnote table h, below). h For NICAM receivers, the relationship between the levels of alignment level tones transmitted by the broadcasting authorities and the maximum digital coding level, and between the levels of alignment level tones in mono and stereo modes, may vary in different countries. See:
a) EBU Techn. SPB 424 (3rd Ed.)
b) NICAM 728: Specification for two additional digital sound channels with system I television, IBA, BREMA and BBC, London 1988.
8.2.2 Interfaces for professional equipment and consumer equipment where audio and video signals are present on the same connector or cable Table 3 gives the values for audio signals for professional interfaces. This table does not apply to interfaces for broadcasting equipment. See Table 14. SIST EN 61938:2019

– 18 – IEC 61938:2018 © IEC 2018 Table 3 – General purpose values for audio signals for professional interfaces Output a Input
Recommended values
Recommended values Output source impedance ≤1 kΩ Rated source impedance 1 kΩ Rated load impedance 10 kΩ g Input impedance ≥10 kΩ Rated output voltage 0,5 V b Rated source e.m.f. 0,5 V e Minimum output voltage 0,2 V c Minimum so
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