IEC 61937-3:2017

Overview

IEC 61937-3:2017 is Part 3 of the IEC 61937 series and specifies how to carry non‑linear PCM encoded audio bitstreams formatted as AC‑3 and enhanced AC‑3 (E‑AC‑3) over a digital audio interface that applies IEC 60958. This third edition supersedes the 2007 edition and is a technical revision that, among other changes, removes support for E‑AC‑3 at 32 kHz, updates references, and clarifies pause data‑burst behavior for enhanced AC‑3.

Key topics and technical requirements

• Purpose: Defines mapping of AC‑3 / enhanced AC‑3 syncframes into IEC 61937 data‑bursts and the associated control information (burst‑info).
• Burst‑info: A 16‑bit header field that identifies the data type (AC‑3 vs E‑AC‑3), repetition period and other data‑type dependent info required by receivers to recognize and process bursts.
• Data‑burst structure: Each audio data‑burst contains a burst preamble and a burst‑payload carrying one complete AC‑3 or E‑AC‑3 syncframe. An AC‑3 syncframe represents 1 536 samples per encoded channel.
• Reference point (R): The reference point for an AC‑3 data‑burst is defined as the IEC 60958 frame located two‑thirds of the way through the burst‑payload (rounded to the nearest 32‑bit word boundary).
• Pause data‑bursts: Recommended repetition periods are specified to maintain link integrity during gaps. For example, the recommended pause repetition is 3 IEC 60958 frames for AC‑3 and 4 IEC 60958 frames for enhanced AC‑3.
• Latency and synchronization: The standard specifies how to calculate decoder latency and instructs transmitters to use the specified latency values to schedule bursts for picture/audio synchronization. For AC‑3, the decoder latency is defined as one AC‑3 block time (256 PCM samples; e.g., 5.33 ms at 48 kHz).
• Compatibility and constraints: The edition removes E‑AC‑3 support at 32 kHz and updates normative/informative references to align with current codec and interface specifications.

Practical applications and users

• Engineers and system architects designing or integrating digital audio interfaces for consumer AV equipment (AV receivers, set‑top boxes, soundbars).
• Firmware and driver developers implementing IEC 61937 packetization, burst scheduling, and decoder synchronization for AC‑3/E‑AC‑3 passthrough.
• Test and QA teams validating compliance of digital outputs, synchronization of audio/video, and interoperability between IEC 60958 transport layers and AC‑3/E‑AC‑3 decoders.
• Broadcast, streaming and home theater manufacturers ensuring correct transmission of compressed multichannel audio over S/PDIF or similar IEC 60958‑based links.

Related standards

• IEC 61937‑1 (General mapping rules for non‑linear PCM bitstreams)
• IEC 61937‑2 (Burst‑info)
• IEC 60958 (Digital audio interface format / S/PDIF)
• ETSI TS 102 366 (AC‑3 and enhanced AC‑3 bitstream specification)
• ATSC A/52 (AC‑3/ Dolby Digital specification)

Keywords: IEC 61937-3, AC-3, enhanced AC-3, E-AC-3, digital audio interface, IEC 60958, non-linear PCM, data-burst, burst-info, decoding latency, syncframe.