PCM - what is it?

Discussion in 'AV Receivers & Amplifiers' started by JoeA3, Feb 2, 2009.

  1. JoeA3

    JoeA3
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    Hi folks,
    I have my new Pioneer VSX1018 AVR hooked up to my Sony BDP350 blu-ray player.

    When I play a normal DVD, the AVR auto-recognises the format of the soundtrack and it displays on the AVR's display, e.g. "DTS", "Dolby Digital", etc.

    However, for all the Blu-ray discs I try, I only ever see "PCM" displayed. Even when I enter the movie's settings and change it to "True-HD", PCM is still on the display. So I'm not entirely sure if my Amp is decoding the soundtrack correctly.... or not. I kind-of expected the amp to display "True-HD" in this scenario.

    What does "PCM" mean?

    I'm pretty confident nothing is wrong, so I'm more curious than anything if I have everything connected correctly (I have the Blu-ray hooked up via hdmi).
     
  2. Trollslayer

    Trollslayer
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    Pulse Code Modulation - uncompressed digital sound where the values are sent directly to the analogue converters without decoding, use Google if you want more details.
     
  3. Jez1

    Jez1
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    Sounds like the Blu Ray player is doing the decoding for you.
     
  4. JoeA3

    JoeA3
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    Cheers. I'm wondering if that's normal though?

    I checked the audio settings in the blu-ray player, and all seemed normal, there are options to change what to output via coax/optical, but none of those settings made any difference to what goes out via HDMI (and I'm only using a hdmi lead from blu-ray to AVR)
     
  5. Jez1

    Jez1
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    I don't know enough about HD-audio to know whether you can push that decoding work back to the amp or not, or whether to do so is generally desirable. I know the recommendation with PS3s seems generally to be let the player decode and then let the amp just take LPCM through the HDMI input.

    I'll let the HD-audio experts comment from now on.
     
  6. Jez1

    Jez1
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    This link may help you if you want to force your receiver to decode those formats which it can,

    Sony BDP-350 Audio Settings - Home Theater Forum

    Mix: Player decodes everything that it can, sends PCM to receiver.
    Direct: "bitstream" setting, for receivers that *can* decode the TrueHD/DTS-HD etc. codecs, sends raw undecoded data to receiver. But on a receiver that can't decode, in theory it will revert back to "mix" behavior anyway after it negotiates and finds the receiver can't handle it.

    Suggests that if you change "BD-Audio" to "Direct" then your receiver will negotiate with the player about which formats it can decode, and the player will send those ones through direct to it without decoding itself.

    Hope I've understood this right, and that it's some help to you.
     
  7. topcourier

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    You need to know if your player can send the signal as a bitstream, that way the amp will decode it into TrueHD. If your player can't do this scroll through the surround settings on the amp, When the amp says Multichannel or PCM this is the same sound quality. Hope this helps and either way you are not missing out on anything. :smashin:
     
  8. JoeA3

    JoeA3
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    Yeah, I had quick a look at the Sony 350 owners forum on here just now, and many people suggest changing the "BD Audio" to "Direct" instead of the default "Mix". This should make the AMP decode the HD audio rather than the player... I think!

    I'm not sure does it make any difference whether the Amp does the decoding or the player though.
     
  9. chic

    chic
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    to be honest i dont think there is much difference between both methods, i have a ps3 which decodes the hd audio and a samsung bdp 1500 which sends the hd audio in bitstream format for my amp to decode and i cant tell much difference between both methods. However if you want your amp to light up with true hd etc you need to go the bitstream way.
     
  10. Jed C

    Jed C
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    Hi Joe,

    Nothing is straight forward in this AV world, as discussed with you before i have this amp on auto and my Pioneer 51 bluray sending bitstream, letting the amp decode, ive listened to a true HD soundtrack this way and via PCM, to be honest i preferred the amp doing the decoding.

    I may just be trying to convince myself i can hear a difference though...... well maybe ?
     
  11. JoeA3

    JoeA3
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    Haha, cheers Jed. I think I'd like to see the Amp doing it also - I mean, that's what I bought it for :thumbsup:
     
  12. topcourier

    topcourier
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    Just something nice about seeing the words, TrueHD written on the amp.
     
  13. sneeks

    sneeks
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    So long as I use my PS3 for BD playback I'll never get to see those words lit on my Denon 1909 :(
     
  14. Jamie

    Jamie
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    The player doing the decoding is actually the "correct" way. According to the profile 1.1 and 2.0 specs (i.e. the Blu ray live nonsense) the decoding should be done at source else the extras (commentary, mixs etc) wont work. You'll just hear the main sound track.

    Ultimately should Blu-ray be still around in years to come then I personally envision decoding on the amp to be less common. Its only included at the moment for backwards compatibility with older players and as a spec box for the manufacturer to tick.
     
  15. JoeA3

    JoeA3
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    Yeah, I tend not to bother with most of the "extras" on discs these days anyhow, I certainly could not be bothered with that BD Live stuff. My main concern is watching the main feature in the best possible video & audio quality.
     
  16. Jamie

    Jamie
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    Fair enough.

    In theory there should be no difference. HD soundtracks are lossless, so wherever its decoded the results will be the same.
    Funnily enough though I have heard plenty of people express a preference for bit streaming and amp decoding over player decosing and LPCM. No idea why

    Personally I believe these differences are either the amp applying different processing to different inputs. Or just not there at all. But not hearing it myself I don't want to say point blank there is no difference. I'm perfectly willing to accept there might be. (even though technically there shouldn't be)
     

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