EDID and capabilities

Short audio descriptor

How an EDID declares audio formats

A sink does not tell a source that it does surround. It sends a list of short audio descriptors, and the source sends only what is on that list. On the Diva you decide what that list contains.

Short audio descriptors live in the audio data block of the CEA extension inside an EDID. Each descriptor is three bytes and describes exactly one format: a format code such as LPCM, AC-3, DTS, Dolby Digital Plus, DTS-HD or MAT for TrueHD, the maximum number of channels, and the sample rates supported. For LPCM the third byte lists the bit depths; for the compressed formats it gives a maximum bit rate.

A source reads the whole list and sends the best thing on it that it has. The consequence is blunt: a format with no descriptor is a format that will never be sent, however capable the equipment at the far end is. Most complaints that a soundtrack refuses to appear are a missing descriptor rather than a decoding failure, which is why the fix usually happens in the EDID and not in the player menu.

The list also has to be honest in the other direction. Descriptors are a promise, and a source that is promised a format will send it whether or not the device that eventually has to decode it can do so.

Short audio descriptors on the HDfury Diva

The 90 predefined EDID tables are laid out as a video format, a colour and HDR variant, then one of three audio levels: all sound, S/PDIF or stereo. Tables 17, 18 and 19 are the same 4K60-444 600MHz video description with All Sound, SPDIF and Stereo audio respectively. Picking a table in CUSTOM mode is therefore picking a set of descriptors, and each input can be given its own table.

AUTOMIX builds the list instead of choosing it, from the mutual capabilities of the sinks actually connected, then lets you override the parts you care about with flags. The manual's own example is the common one: a stereo television and a full sound AVR both connected, and Automix reporting stereo because that is what the two agree on. Ticking the full audio flag makes the mixed EDID always report full audio. Over IP the command is set edid audio, whose values are stereo, 51, full, native and tx1.

2.0 Stereo

Force the mixed EDID to present stereo capabilities only.

5.1 Multi

Force 5.1 multi-channel capabilities.

7.1 Full

Force full 7.1 capabilities regardless of what the sinks claim.

TX0 and TX1

Force the audio capabilities of the sink connected at that output.

AUDIO OUT

Force the audio capabilities of the sink at the dedicated HDMI audio output, which is the one to use when your AVR is fed from there.

All glossary terms