Audio
Bitstream
Sending compressed audio untouched
In short
Sending compressed audio onward in its original encoded form, so the receiving device rather than the source does the decoding.
Bitstream is the setting on your source that says do not decode this, pass it on. Whether it survives the trip depends on the output you take it from and on what the source was told the chain accepts.
An HDMI link carries audio in one of two forms. LPCM is already decoded, a stream of samples per channel. A bitstream is the compressed original, Dolby Digital, Dolby Digital Plus, Dolby TrueHD, DTS-HD Master Audio and the rest, handed over untouched for the receiving end to decode.
Which is better depends on where the decoding is best done. Bitstreaming lets a receiver apply its own decoder and post processing, and it is the only way to get the object metadata of Dolby Atmos or DTS:X across, because the objects travel inside the compressed stream. LPCM is the answer when the source does something the receiver cannot, or when a device in the middle only passes two channels.
The catch is that a bitstream is all or nothing. A device that cannot decode a format hears silence rather than a reduced version of it, and the lossless formats need the high bit rate carriage that only an HDMI or eARC link provides.
How the HDfury Diva handles a bitstream
The Diva performs no audio format manipulation: what comes in goes out untouched. It does not compress or downconvert the incoming audio, so lossless formats such as DTS-HD Master Audio and Dolby Digital Plus are transmitted through the HDMI outputs only. Only stereo and 5.1 sound can leave by the S/PDIF output, and the analogue side of that jack is stereo alone.
That single rule decides your cabling. A TrueHD or DTS-HD Master Audio bitstream reaches a receiver through the dedicated HDMI audio output, a self-generated 720p or 1080p video stream carrying full audio and made to feed any AVR input. If your only link to the amplifier is the optical jack, the source has to be sending something an optical link can carry in the first place.
What the source sends is decided by the EDID it reads. In AUTOMIX the flags 2.0 Stereo, 5.1 Multi and 7.1 Full force the mixed EDID to present those capabilities, and AUDIO OUT forces it to present the maximum audio capabilities of the sink at the audio output, which is the one to use when the amplifier is fed from there. Over RS232 or IP it is set edid audio full.
Checking what is actually arriving
The HDR/DV section captures the audio infoframe. AUD INFOFRAME reports the audio format information: for PCM it usually gives the sample rate and number of speakers, and for bitstream it usually reports the default, refer to stream header. That is not a fault. A bitstream describes itself in its own header, so the infoframe has little to add.
The AUDIO TX0 and AUDIO TX1 rows in the INFO section report the audio leaving each output, and REFRESH is needed after a disc or app change because the page does not update itself.
Related terms
In the manual
The pages of the HDfury Diva manual where this comes up.