HDfury Diva

Audio

LPCM

Linear Pulse Code Modulation, uncompressed audio

In short

Uncompressed digital audio sent as raw samples, rather than as a coded bitstream the receiving device has to decode first.

LPCM is what every other format becomes once it has been decoded. Whether your source sends it, and with how many channels, is decided by the EDID the Diva presents.

LPCM stands for Linear Pulse Code Modulation. It is digital audio in its plainest form: the waveform is measured at a fixed rate and each measurement is stored as a number on a linear scale, with no compression and nothing for the receiving device to decode. A 48kHz 24-bit stereo track is LPCM, and so is an eight channel 192kHz one.

Everything else on HDMI is a bitstream. Dolby Digital, DTS-HD Master Audio, TrueHD and their Atmos variants are coded formats that an AVR unpacks into LPCM before it drives a single speaker. Choosing between LPCM and bitstream decides which end of the chain does the decoding, not how good the result is, although only bitstream carries the object metadata that Atmos depends on.

LPCM is expensive in bandwidth, and the EDID has to allow for it. A sink declares how many channels and which sample rates it accepts in its short audio descriptors, and a source will not send more than it finds there.

LPCM through the HDfury Diva

The Diva performs no audio format manipulation at all. What comes in goes out untouched, so it neither packs LPCM into a bitstream nor decodes a bitstream into LPCM. That single fact answers most audio questions about the unit: if you want stereo from the analogue jack, the signal arriving at the input must already be stereo, and a source sending Atmos leaves that output unusable.

What you do control is what the sources are told. The predefined EDID tables come in three audio levels, All Sound, SPDIF and Stereo, so table 11 is 4K60-444 600MHz HDR BT2020 All Sound while table 13 is the same video description with stereo only. FIXED EDID presents a 4K60 4:2:0 8-bit 300MHz 2-channel audio table, which is the safe thing to fall back on when sound has gone missing.

In AUTOMIX the flags 2.0 Stereo, 5.1 Multi and 7.1 Full force the mixed EDID to present those capabilities whatever the sinks claim. The command is set edid audio full, and the permitted values are stereo, 51, full, native and tx1.

Related terms

BitstreamSending compressed audio onward in its original encoded form, so the receiving device rather than the source does the decoding.Short audio descriptorA three-byte entry in an EDID that names one audio format a display or amplifier accepts, with its channel count and sample rates.S/PDIFA two channel digital audio interface, on optical or coaxial cable, which can also carry a compressed multichannel bitstream.Audio extractionTaking the audio out of an HDMI stream and delivering it on a separate output, so a receiver can hear it without having to handle the video.

In the manual

The pages of the HDfury Diva manual where this comes up.

All glossary terms