IEC 61938:2018

Overview

IEC 61938:2018 - "Multimedia systems - Guide to the recommended characteristics of analogue interfaces to achieve interoperability" - is an IEC technical guide that provides recommended characteristics for analogue multimedia interfaces so equipment from different manufacturers can interoperate. It is a guidance document (not a performance standard) and covers recommended electrical values, connection practices and interface characteristics for audio and general multimedia analogue interconnections. The third edition (2018) cancels and replaces the 2013 edition and introduces standardized electric tolerances, adjusted output source impedance recommendations and an added 6 Ω recommendation for impedance‑defined loudspeaker systems.

Key technical topics and requirements

• Scope and exclusions: Guidance applies to multimedia analogue interfaces but excludes specific recommendations for vehicle equipment and analogue video interfaces for broadcast and similar professional broadcast equipment. For digital interconnections see IEC 60958.
• Power supply: Recommended AC and DC supply voltages and tolerances; guidance for microphone powering methods (plug‑in power, soundcard power, phantom power, A‑B supply).
• Interconnections and connectors: Cable characteristics, pairing and screening; connector practice to support reliable analogue signal transfer and interoperability.
• Electrical recommended values: General purpose audio, video and signal values presented in industry‑oriented tables (audio-only consumer, professional audio, video).
• Microphones, amplifiers and headphones: Recommended values and interoperability practices including phantom power requirements, polarities, output/input impedances and recommended values for portable and stationary headphone applications.
• Loudspeakers and amplifiers: Recommendations for single unit loudspeakers, impedance‑defined and constant voltage systems; voltage/power interoperability guidance.
• Tables and diagrams: Practical tables for values (power, impedances, recommended levels) and circuit examples for microphone power variants.
• Marking and symbols: Recommended marking practices for interfaces and power supplies.

Practical applications and who uses this standard

IEC 61938 is used by:

• Audio/video equipment manufacturers designing analogue inputs/outputs to ensure cross‑brand compatibility.
• System integrators and installers specifying interconnects and powering methods for multimedia installations.
• Product designers and electrical engineers setting connector, impedance and power‑supply characteristics.
• Test laboratories and quality assurance teams verifying that analogue interfaces conform to recommended interoperability characteristics.
• Audio professionals (recording, sound reinforcement) and specification writers wanting industry best‑practice reference values.

Practical benefits include fewer compatibility issues between devices, clearer design targets for analogue interfaces, and harmonized values for microphone powering, impedance matching and connector wiring.

Related standards / references

• IEC 60958 - for interconnection of digital signals (recommended cross‑reference in this guide).
• Other IEC publications referenced for terminology and related multimedia/electrotechnical practices.

Keywords: IEC 61938, analogue interfaces, multimedia systems, interoperability, audio interfaces, phantom power, microphone powering, loudspeaker impedance, connector standards.