EN 61938:1997

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Audio, video and audiovisual systems - Interconnections and matching values - Preferred matching values of analogue signals (IEC 61938:1996)Audio-, Video- und audiovisuelle Anlagen - Zusammenschaltungen und Anpassungswerte - Empfohlene Anpassungswerte für analoge SignaleSystèmes audio, vidéo et audiovisuels - Interconnexions et valeurs d'adaptation - Valeurs d'adaptation recommandées des signaux analogiquesAudio, video and audiovisual systems - Interconnections and matching values - Preferred matching values of analogue signals35.200Vmesniška in povezovalna opremaInterface and interconnection equipment33.160.01Avdio, video in avdiovizualni sistemi na splošnoAudio, video and audiovisual systems in generalICS:Ta slovenski standard je istoveten z:EN 61938:1997SIST EN 61938:1999en01-april-1999SIST EN 61938:1999SLOVENSKI
STANDARD
NORMEINTERNATIONALECEIIECINTERNATIONALSTANDARD1938Première éditionFirst edition1996-12Ó CEI 1996
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catalogueTSystèmes audio, vidéo et audiovisuels –Interconnexions et valeurs d’adaptation –Valeurs d’adaptation recommandéesdes signaux analogiquesAudio, video and audiovisual systems –Interconnections and matching values –Preferred matching values of analogue signalsSIST EN 61938:1999

1938 © IEC: 1996– 3 –CONTENTSPageFOREWORD.
7Clause1General.
111.1Scope.
111.2Normative references.
112General conditions and definitions. 132.1General conditions.
132.2Definitions.
133Power supply.
173.1Alternating current (a.c.) power supply voltages and frequencies.
173.2Direct current (d.c.) power supply voltages.
173.3Power supply feed for microphones.
174Interconnections.
174.1Connections.
154.2Connectors. 215Marking and symbols for marking. 215.1Marking. 215.2Symbols for marking. 216Electrical matching values. 216.1General purpose output/input. 216.2General purpose audio output/input. 236.3General purpose video input/output. 277Matching of microphones and amplifiers. 297.1Microphones (excluding piezoelectric types).297.2Microphones with built-in amplifier.317.3Power supply feed for electret microphones fed by a separate conductor. 317.4Phantom supply system. 317.5A-B supply system. 337.6Polarity of the audiofrequency voltage. 338Matching of record-playing units (pick-ups) and amplifiers. 339Matching of loudspeakers and amplifiers. 379.1Single unit loudspeakers. 379.2Loudspeaker systems. 379.3Voltage (or power) matching of amplifiers and loudspeakers. 399.4Polarity of the sound pressure. 4110Matching of headphones and amplifiers. 4111Matching of amplifiers to amplifiers. 4111.1Pre-amplifiers and power amplifiers for general purpose andsound reinforcement. 4111.2Broadcast and similar line amplifiers. 43SIST EN 61938:1999

1938 © IEC: 1996– 5 –TablesPages1Direct current (d.c.) power supply voltages and tolerances.
172General purpose matching values for audio signals. 233General purpose matching values for video signals. 274Matching values for microphones and amplifiers. 295Matching values for analogue record-playing units and amplifiers. 356Matching values for impedance-defined loudspeaker systems. 377Matching values for constant voltage loudspeaker systems. 378General purpose matching values for headphones and amplifiers. 419Matching values for pre-amplifiers and power amplifiers. 4310Matching values for broadcast and similar line amplifiers. 4311Required values for phantom supply systems. 4712Required values for A-B power supply systems.49Figures1Audio and video sources and destinations. 452Example of phantom power supply system. 473Example of A-B power supply system. 49SIST EN 61938:1999

1938 © IEC: 1996– 7 –INTERNATIONAL ELECTROTECHNICAL COMMISSION_____________AUDIO, VIDEO AND AUDIOVISUAL SYSTEMS –INTERCONNECTIONS AND MATCHING VALUES –PREFERRED MATCHING VALUES OF ANALOGUE SIGNALSFOREWORD1)The IEC (International Electrotechnical Commission) is a worldwide organization for standardizationcomprising all national electrotechnical committees (IEC National Committees). The object of the IEC is topromote international co-operation on all questions concerning standardization in the electrical and electronicfields. To this end and in addition to other activities, the IEC publishes International Standards. Theirpreparation is entrusted to technical committees; any IEC National Committee interested in the subject dealtwith may participate in this preparatory work. International, governmental and non-governmental organizationsliaising with the IEC also participate in this preparation. The IEC collaborates closely with the InternationalOrganization for Standardization (ISO) in accordance with conditions determined by agreement between thetwo organizations.2)The formal decisions or agreements of the IEC on technical matters, express as nearly as possible, aninternational consensus of opinion on the relevant subjects since each technical committee has representationfrom all interested National Committees.3)The documents produced have the form of recommendations for international use and are published in theform of standards, technical reports or guides and they are accepted by the National Committees in thatsense.4)In order to promote international unification, IEC National Committees undertake to apply IEC InternationalStandards transparently to the maximum extent possible in their national and regional standards. Anydivergence between the IEC Standard and the corresponding national or regional standard shall be clearlyindicated in the latter.5)The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for anyequipment declared to be in conformity with one of its standards.6)Attention is drawn to the possibility that some of the elements of this International Standard may be thesubject of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.International Standard IEC 1938 has been prepared by subcommittee 100C*: Audio, video andmultimedia subsystems and equipment, of IEC technical committee 100: Audio, video andmultimedia systems and equipment.International Standard 1938 cancels and replaces IEC 268-15, published in 1996, andIEC 574-4, published in 1982, and constitutes a technical revision.The text of this standard is based on the following documents:FDISReport on voting100C/22/FDIS100C/51/RVDFull information on the voting for the approval of this standard can be found in the report onvoting indicated in the above table.––––––––––* Formely technical committee 84.SIST EN 61938:1999

1938 © IEC: 1996– 9 –The standard is derived from IEC 268-15, IEC 574-4 and IEC 933-1 and also from relatedproposals which have been submitted up until today.The interconnection of digital signals is excluded, as it is preferred to prepare a separatepublication for it.The features of the revision are as follows:1)Unification and arrangement of existing related standards, including effective proposalswhich have been submitted.2)The concept of "general purpose input/output".3)This standard supersedes and replaces:IEC 268-15 and amendmentsIEC 574-4 and amendments.SIST EN 61938:1999

1938 © IEC: 1996– 11 –AUDIO, VIDEO AND AUDIOVISUAL SYSTEMS –INTERCONNECTIONS AND MATCHING VALUES –PREFERRED MATCHING VALUES OF ANALOGUE SIGNALS1 General1.1 ScopeThis International Standard applies to electrical matching values for the interconnection ofanalogue signals amongst audio, video and AV system equipment.This standard includes audio but not video signals for broadcast and similar use.Interconnections using the 21 contact connector described in IEC 807-9 are not included in thisstandard.Matching values for vehicle applications are excluded.For the interconnection of digital signals, it is necessary to refer to IEC 958.NOTE – A diagram showing possible interconnections, with cross-references to the appropriate clauses, is givenin figure 1.1.2 Normative referencesThe following normative documents contain provisions which, through reference in this text,constitute provisions of this International Standard. At the time of publication, the editionsindicated were valid. All normative documents are subject to revision, and parties toagreements based on this International Standard are encouraged to investigate the possibilityof applying the most recent editions of the normative documents listed below. Members of IECand ISO maintain registers of currently valid International Standards.IEC 27: Letter symbols to be used in electrical technologyIEC 38: 1983, IEC standard voltages, Part 1: General conditions and requirementsIEC/DIS 50(723): International Electrotechnical Vocabulary (IEV) – Chapter 723: Broadcasting:Sound, television and dataIEC 94-2: 1994, Magnetic tape sound recording and reproducing systems – Part 2: CalibrationtapesIEC 107-6: 1989, Recommended methods of measurement on receivers for televisionbroadcast transmission – Part 6: Measurement under conditions different from broadcast signalstandardsIEC 268-5: 1989, Sound system equipment – Part 5: LoudspeakersIEC 268-7: 1984, Sound system equipment – Part 7: Headphones and headsetsSIST EN 61938:1999

1938 © IEC: 1996– 13 –IEC 268-11: 1987, Sound system equipment – Part 11: Application of connectors for theinterconnection of sound system componentsIEC 268-12: 1987, Sound system equipment – Part 12: Application of connectors for broadcastand similar useIEC 417: 1973, Graphical symbols for use on equipmentIEC 617: Graphical symbols for diagramsIEC 807-9: 1993, Rectangular connectors for frequencies below 3 MHz – Part 9: Detailspecification for a range of peritelevision connectorsIEC 958: 1989, Digital audio interfaceIEC 1293: 1994, Marking of electrical equipment with ratings related to electrical supply –safety requirementsISO/IEC 2382-9: 1995, Data processing – Vocabulary – Part 9: Data communicationITU-R BT.470-4: 1995, Television systems2
General conditions and definitions2.1 General conditionsAll 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, unlessotherwise indicated.2.2 DefinitionsFor the purposes of this International Standard, the following definitions apply:2.2.1
luminance signal: An electrical signal representing the luminance of the televisionpicture elements. [IEV 723-05-56]2.2.2
chrominance signal: An electrical signal that is associated with the luminance signal toconvey colour information. In practice this signal is made up of two components. [IEV 723-05-57]2.2.3
Y" signal, VBS signal: The Y" signal is a combined signal consisting of–a luminance signal;–blanking and synchronizing signals.NOTE – The Y" signal equals the composite video signal (CVBS signal) without the C" signal.2.2.4
colour signal, C" signal: A chrominance signal with burst signal included, modulatedon a subcarrier.SIST EN 61938:1999

1938 © IEC: 1996– 15 –2.2.5
blanking signal: Signal used to control the suppression of the signal conveyingpicture information during certain parts of the scanning period, for example, during fly-back.[IEV 723-05-37]2.2.6
synchronizing signal: A signal used to determine the timing for the scanningprocesses in transmission and reception. [IEV 723-05-36]2.2.7
composite video signal, composite video blanking synchronization or CVBSsignal: The composite video signal is a combined signal consisting of:–a luminance signal;–a colour signal;–blanking and synchronizing signals.2.2.8
interface: A shared boundary between two pieces of equipment, defined by functionalcharacteristics, common physical interconnection characteristics, signal characteristics andother characteristics, as appropriate. [ISO/IEC 2382-9, modified]2.2.9
minimum output voltage: The voltage measured across the rated load impedance of apiece of equipment, and related to a minimum input signal limited by signal to noise ratio.2.2.10
maximum output voltage: The voltage measured across the rated load impedance ofa piece of equipment and related to a maximum input signal limited by non-linearity.2.2.11
rated source impedance: The internal impedance, stated by the manufacturer, of thesource supplying the signal to the piece of equipment. Unless otherwise specified, the ratedsource impedance is assumed to be a constant pure resistance.NOTES1The manufacturer may also give the range of source impedances which he considers tolerable in practice.2Multiple values, or a range of values, may be specified, providing the corresponding rated (distortion-limited)output voltages and/or powers are also stated.2.2.12
input impedance: The internal impedance measured between the input terminal andits corresponding return of the piece of equipment.2.2.13
rated source e.m.f.: The e.m.f. specified by the manufacturer which, when connectedto the input terminals in series with the rated source impedance, gives rated distortion-limitedoutput voltage across the rated load impedance at an appropriate setting of the controls.2.2.14
minimum source e.m.f. for rated output voltage: The e.m.f. which, when connectedto the input terminals in series with the rated source impedance, gives rated output voltageacross the rated load impedance with the volume control(s), if any, set for maximum gain andthe tone control(s), if any, set as specified for rated conditions.2.2.15
rated load impedance: The impedance, specified by the manufacturer, to which theoutput terminals are to be connected for measuring purposes. Unless otherwise specified bythe manufacturer, the rated load impedance shall be assumed to be a constant pureresistance.NOTE – Multiple values, or a range of values, may be specified, providing the corresponding rated (distortion-limited) output voltages and/or powers are also stated.SIST EN 61938:1999

1938 © IEC: 1996– 17 –2.2.16
output source impedance: The internal impedance measured between the outputterminal and its corresponding return under specified conditions.2.2.17
rated output voltage: The voltage specified by the manufacturer, measured acrossthe rated load-impedance of a piece of equipment.2.2.18
overload source e.m.f.: The 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, candeliver an output voltage 10 dB below the rated distortion limited output voltage withoutexceeding the rated total harmonic distortion.3 Power supply3.1 Alternating current (a.c.) power supply voltages and frequenciesFor a.c. power supply voltages and frequencies, reference is made to IEC 38.For special applications, for example ships and aircraft, other voltages and/or frequencies andthe permissible tolerances are subject to agreement between manufacturers and users.3.2 Direct current (d.c.) power supply voltagesDC power supply voltages and the permissible tolerances are given in table 1. The equipmentshould operate over the range of voltages given, but may not necessarily meet all of itsspecifications at the given limits.Table 1 – Direct current (d.c.) power supply voltages and tolerancesType of power supplyRatedvoltage/cellOperating voltage/cellVVLower limitNormalvoltageUpper limitPrimary batteries–Alkali-Manganese, zinc chloride-zinc–Lithium (organic electrolyte)1,53,01,02,01,53,01,653,7Secondary batteries:–Lead-acid, except vehicle batteries–Lead-acid, vehicle batteries–Nickel-cadmium2,02,01,21,81,81,12,02,41,22,22,61,43.3 Power supply feed for microphonesReference is made to 7.3, 7.4 and 7.5.4 Interconnections4.1 ConnectionsSignal cables shall have the appropriate electrical characteristics to permit the transfer ofsignals between the parts of a system without unacceptable impairment.SIST EN 61938:1999

1938 © IEC: 1996– 19 –NOTE – The degree of impairment which is unacceptable depends on the system specification and the need tocomply with other international standards, such as those concerning electromagnetic compatibility.4.1.1 Characteristics of cablesThe following characteristics of cables should be taken into account.4.1.1.1 Resistance of the conductorsA resistance of less than one-hundredth of the load impedance is usually acceptable forloudspeaker connections. For other applications, values of one-tenth are acceptable.NOTE – Long cables may therefore require conductors of larger cross-section area than those of short cables.4.1.1.2 Insulation resistanceAn insulation resistance of 50 MW is usually acceptable.4.1.1.3 Inductance of conductorsThis is normally only important for very long cables.The acceptable value varies too widely to give more than general guidance. In the absence ofparticular requirements, the inductive reactance should not exceed one third of the loadimpedance at the highest frequency of interest.NOTES1The inductance of an isolated single conductor (of typical length to diameter ratio of the type of cablenormally used in these applications) is approximately 2 mH/m.2The requirement ensures less than approximately 1 dB loss at the highest frequency of interest.4.1.1.4 Capacitance between conductorsThe acceptable value varies too widely to give more than general guidance. For conductorscarrying different audio signals, and in the absence of particular requirements, the capacitivereactance should exceed 1000 times the load impedance at the highest frequency of interest.NOTE – This ensures that the relative crosstalk level is approximately –60 dB if the two conductors carrysignals at similar levels.4.1.1.5 Capacitance from conductor to screenThe acceptable value varies too widely to give more than general guidance. In the absence ofparticular requirements, the capacitive reactance should exceed three times the sourceimpedance at the highest frequency of interest.NOTE – This ensures less than approximately 1 dB loss at the highest frequency of interest.4.1.1.6 Characteristic impedanceThis is usually only important for high-frequency signals (such as digital signals in accordancewith IEC 958).SIST EN 61938:1999

1938 © IEC: 1996– 21 –4.1.1.7 Continuity of screeningIn some applications, screening should be connected to contacts of connectors at both ends ofthe cable. In other cases, screening should be connected at one end of the cable only (forexample to eliminate circulating currents). Cable and connector assemblies preferably shouldbe marked to show which practice has been applied.The screening of signal cables and connectors shall not be used as a means for thepreservation of safety earth continuity for the prevention of electric shock hazard.4.1.1.8 Efficiency of screeningThe 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 goodperformance in another.4.2 ConnectorsFor connectors used within the system, reference shall be made to the reference documentsgiven in 1.2.5 Marking and symbols for marking5.1 MarkingTerminals 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 positionswith sufficient accuracy in connection with the information given in the user instructions.5.2 Symbols for markingMarking preferably should be composed of letter symbols, signs, numbers and colours, whichare internationally intelligible. Reference is made to IEC 27, IEC 417, IEC 617 and IEC 1293.Markings not included in the above-mentioned standards shall be clearly explained in the userinstructions.6 Electrical matching values6.1 General purpose output/inputIn order to preserve the maximum flexibility of use and compatibility in the design ofequipment, all inputs of destination equipment, and all outputs o
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