IEC 61938-2018 pdf free.Multimedia systems – Guide to the recommended characteristics of analogue interfaces to achieve interoperability.
6.1.2.4 Magnetic and electromagnetic interference susceptibility of interconnectionsThe use of untwisted pairs or single conductors with separate return paths is a commonsource of magnetic and electromagnetic interference at both audio and radio frequencies,especially for loudspeaker wiring, and should be avoided.A description of the methods ofavoiding such interference is given in Annex A.
6.1.2.5Reactance of conductors
The acceptable values vary too widely to give more than general guidance. The cableshould not appreciably affect the signal being carried. ln the absence of particularrequirements,the inductive reactance of the cable should not cause more than 1 dBchange in response over the frequency range of interest. The capacitive reactancebetween the two conductors of a signal-carrying pair,or a coaxial cable, in parallel with theload impedance,should be greater than the rated load impedance,at the highest frequencyof interest.
While it is not recommended to use cables in which single conductors carry different audiosignals，the capacitive reactance between conductors in this case should exceed 1 00otimes the load impedance at the highest frequency of interest.
6.1.2.6Capacitance from conductor to screen
The acceptable value varies too widely to give more than general guidance.In the absence ofparticular requirements, the capacitive reactance of a coaxial cable, in parallel with the loadimpedance,should be greater than the rated load impedance.The capacitance between eachconductor of a balanced pair and its screen should be equal within 7,5 %.A closer toleranceis desirable.
NOTE The 7,5 % tolerance,which can be achieved using normal cable manufacturing methods，ensurespreservation of adequate common mode rejection in balanced circuits (see Whitlock，JAES,1995-O6). Theelectromagnetic interference rejection of such circuits is dependent on impedance balance.
6.1.2.7Characteristic impedance
This is usually only important for high-frequency signals (such as digital signals in accordancewith lEC 60958).
6.1.2.8Continuity of screening
ln some applications，the screen is connected to contacts of connectors at both ends of thecable. ln other cases, the screen is connected at one end of the cable only. When the screenof a balanced cable is interrupted, for example to prevent the flow of circulating currents,suchinterruption should be at the receiving end of the signal path. The screen of a coaxial cableshould not be interrupted. Connections between equipment should comply with therequirements of AES48.
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.IEC 61938 pdf download.