What exactly does HDMI audio AUTO setting do?

Discussion in 'HDD Media player(RTD 1295)' started by Ekstravertas, Jan 1, 2021.

  1. Ekstravertas

    Ekstravertas New Member

    First of all Happy New Year to everyone!
    Can someone help me to understand what exactly does AUDIO>HDMI>AUTO setting do? I know it's recommend to leave it on RAW in order to get bit by bit perfect uncompresed sound.
    The thing is that some time, when it's late and I don't want to much noise watching movie, I watch it not through my receiver, but simply through TV speakers. In that case if I leave this setting on RAW, there is naturally no sound from my TV in 5.1 movies. If I leave it on AUTO, I can watch movie on my TV, or in 5.1 through my receiver. But does it mean that on AUTO, all my 5.1 sources (let's say multichannel music) is not bit by bit perfect anymore and are compressed? Or does AUTO setting chage from RAW (if I listen to 5.1 music through receiver) to some other and somehow adapts sound when I simply watch movie on TV?

    TL; DR. Do I lose quality of sound if I set it to AUDIO>HDMI>AUTO?
     
  2. videobruce

    videobruce Member

    I would assume it would allow auto sensing for RAW to PCM and vice-a-versa.
     
  3. Superdog

    Superdog Member

    My Sound HT-X8500 sound bar get no sound when playing DTS 5.1 videos if I set HDMI audio to RAW. But Sony said it can support all Dolby DTS decode and TrueHD can use RAW setting. Only DTS 5.1 needs auto.
     
  4. little-endian

    little-endian New Member

    Your questions are perfectly valid, as Zidoo's documentation is quite terrible on that, to say the least.

    First of all, "RAW" doesn't necessarily mean that it is "uncompressed". The lossless versions of Dolby and DTS with their fancy (and mostly misleading) marketing names such as "TrueHD" or "DTS-HD Master Audio" are just those variants which impose compression comparable to FLAC or WavPack (just less efficient) and with more expensive licensing fuss.

    Technically, "RAW" in this settings section would mean "any audio data taken from the demultiplexer and more or less interleaved into the HDMI output", however, the description used by Zidoo here is also misleading and incorrect as it turns out that for instance audio formats such as AAC or FLAC are very well decoded into a (multichannel) PCM stream, which isn't "RAW" anymore either. Reason for that is, there is virtually no AVR available with decoders for AAC, Vorbis or FLAC on board.

    Furthermore it is inconsequent as their (recent) players seem to lack the ability to decode (E-)AC3/True-HD or DTS(-HD) to multichannel PCM. Hence that option would rather be called "bitstreaming or decoding, depending on the codec".

    Let me guess. I happens with movies either encoded in Dolby TrueHD/Atmos, E-AC3 or DTS-HD. In the "RAW" setting, they would be send "as is" which your TV most probably doesn't support and then muting the output.

    Although I've only tested this on my "Orbsmart R81" which seems to be a rebranded Zidoo Z9X whereas both probably behave very similar, I come to the following conflusion:

    Given a receiver which doesn't support the compressed formats and tell that to the player through their EDID information via HDMI, "AUTO" will instead bitstream the "core" of the corresponding audio code. With Dolby TrueHD this will be the connected AC3 counterpart and with DTS-HD it will be the DTS-Core.

    Before going into that, some clarification about "compression" as this term gets constantly confused by people:

    "Compression" has two meanings:

    1. In conjunction with dynamic ranges, it means the reduction of it. That can happen during production or afterwards during playback (such as the "midnight mode", some AVRs feature).

    2. Reduction of redundancy and optimisation of encoding efficiency to reduce the amount of data. This part is lossless, like well-known archivers such as 7-Zip, RAR, CAB or audio-specialized ones like FLAC do it.

    What often is called compression for codecs such as MP1/2/3, AAC, Vorbis, AC3, DTS, etc. is actually "data reduction" and lossy by definition. So you can measure the difference, but that doesn't necessarily mean that you can also hear it.

    The latter one you most probably will get on your TV in the AUTO mode. You'll hear the technically-on-paper inferior version, but at the regular bitrates of 640 kbps for AC3 or ~ 1500 kbps for DTS virtually no chance of standing a blind-test anyway so free yourself from the (unfortunately well-working) marketing-voodoo. Effectively you won't miss anything, expect if it is about the more of channels (> 6.1) or stuff like object based codecs such as Dolby Atmos.

    From what I've seen (or rather heard), those Zidoo players either convert the multichannel codecs in stereo PCM only or extract the core.

    Effectively not really. If your end device doesn't support any lossless compressed codecs but multichannel PCM, you would need a player which provides you multichannel PCM out of TrueHD/DTS-HD.
     
    videobruce likes this.
  5. Fatih Durmus

    Fatih Durmus Member

    Is Orbsmart R81 support netflix primevideo and other streaming services?
     

Share This Page