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PCM stream or bit stream

Discussion in 'HD DVD discussion' started by gotpitino, Jun 11, 2007.

  1. gotpitino

    gotpitino Member

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    What is the difference between the 2? Is there an audible difference that can be heard?
     
  2. eatsushi

    eatsushi Regular member

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    Excellent questions.

    What's the difference between the two?

    Bitstream

    Bitstream audio refers to a succession of 1's and 0's transmitted from a player typically to a receiver or A/V preamp. The receiver then decodes this information and amplifies the resulting audio signal to drive your speakers. This information can be transmitted either through SPDIF (optical or digital coax) or HDMI connections depending on the compression method.

    Bitstream audio as it comes on disc is usually compressed in 2 ways:

    Lossy compression such as:
    Dolby Digital
    Dolby Digital Plus
    DTS
    DTS HD High Resolution

    Lossless compression such as:
    Dolby True HD
    DTS HD Master Audio

    PCM

    PCM or Pulse Code Modulation "is a digital representation of an analog signal where the magnitude of the signal is sampled regularly at uniform intervals, then quantized to a series of symbols in a digital (usually binary) code." (From the PCM WIkipedia article.) There are compressed forms of PCM audio but the PCM soundtracks that you see in BluRay discs are uncompressed.

    Linear PCM or LPCM can be included on the disc itself or the player can derive LPCM from other digital tracks and transport this through the player's digital connections.

    Is there an audible difference?

    Given the right equipment and the right conditions a compressed lossless Dolby True HD soundtrack should sound the same as an uncompressed LPCM soundtrack.

    See this comparison between the two on "The Departed." The LPCM soundtrack is on the BluRay disc and the Dolby True HD trak is on the HD DVD disc:

    http://hddvd.highdefdigest.com/departed.html

    As long as the Dolby True HD soundtrack is decoded properly, the resulting LPCM signal should be exactly the same as the uncompressed LPCM track or the studio master.

    Maybe Ced or anyone else can add to this?
     
    Last edited: Jun 11, 2007
  3. gotpitino

    gotpitino Member

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    Excellent Information, Thanks.

    But I guess my ultimate question is this.

    I've ordered the Toshiba HD-A2 and the Onkyo TX-SR805.
    Now being that the HD-A2 is not HDMIv1.3, would the TrueHD or DD+ from the A2 sound just as good as the TrueHD and DD+ from, say the XA2 which is HDMIv1.3?
     
  4. eatsushi

    eatsushi Regular member

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    You can get Dolby True HD from the A2 since it can decode this format and transmit this to the receiver using HDMI or analog 5.1. You don't need HDMI 1.3 to do this.

    For the XA2 you have 2 choices: (1) you can let the player decode the Dolby True HD soundtrack and send it to the the receiver like the A2 above. (2) you can send the undecoded signal to the receiver using HDMI 1.3 and let the Onkyo do the decoding.

    I'm not sure of the specs or what audio decoding chip the A2 has but as long as it does its job there should be no or only minimal difference between the audio as decoded by the A2 and the XA2.


    ADDED:

    Here's a comparison of LPCM and Dolby True HD on the same disc!:

    http://bluray.highdefdigest.com/ghostrider.html

     
    Last edited: Jun 12, 2007
  5. diabolos

    diabolos Guest

    You mean the HD-XA2? The A2 doesn't have 5.1 analog outs. The simple answer their is no difference in PCM tracks of the Dolby TrueHD tracks. If there where the Dolby TrueHD wouldn't be all that lossless.

    HD players that don't have HDMI 1.3 support can only send the Dolby TrueHD (or any advanced audio codec, i.e. DD+, DTS-HDMA lossless, ect...) signal, to a receiver that supports HDMI audio, as M-PCM (Multi-Channel Pule Code Modulation, uncompressed) with as many channels and at the same fidelity as the source (i.e. 24 bit/192KHz with 7.1 channels).

    To my knowledge they use the same 32-bit "SHARK" processor by Analog Devices.


    How HD players work (the audio side):
    http://www.dolby.com/consumer/technology/trueHD/avrs/trueHD_avrs_1.html

    -Ceddie Ced
     
    Last edited by a moderator: Jun 13, 2007
  6. eatsushi

    eatsushi Regular member

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    I stand corrected Ced. The HD-A2 does not have 5.1 analog outs. The Dolby True HD can be sent thru HDMI on that model. I must have been thinking of the A1 (which I still have).
     
  7. diabolos

    diabolos Guest

    Its all good. Yea, the A-1 was a great deal for that reason. I don't know why Toshiba doesn't have them on the A-20 as jut about all of the blu-ray players have 6CH analog outputs. I guess with the issue the XA-2 is having it would have been a bad move. I think they should come out with a XA-20 model that has everything a player could offer for $1,000 and mark everything else down including the 360 add-on!

    Thanks for reading my rant,
    Ced
     
  8. gotpitino

    gotpitino Member

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    About the Highdefdigest review of The Departed on Blu-ray and HD DVD. Since no players can actually send the signal bitstream.
    Weren't they just comparing PCM to PCM except on different formats?

    Does this question make sense?

    I mean, nobody is going to be able to compare HD DVD's with TrueHD to Blu-ray's with uncompressed 5.1 until TrueHD can actually be bitstream'd to the receiver, right?
     
  9. diabolos

    diabolos Guest

    No. As Dolby TrueHD isn't suppose to sound better anyway. The bar is PCM and Dolby TrueHD should reach it without a problem as it is suppose to be lossless.

    What I mean is that Dolby TrueHD doesn't contain any more sound than PCM does. Dolby TrueHD just uses less space to accomplish the same thing as PCM. The thing to worry about are the specs (i.e. 16 bit/48 KHz).

    -Ceddie Ced
     
  10. eatsushi

    eatsushi Regular member

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    Ced is correct. What they're comparing are the same exact product but in 2 different packages.

    Actually the XA2 and the PS3 have HDMI 1.3 so they can send the Dolby True HD and DTS HD MA bitstream to a receiver that can decode these signals.
     
    Last edited: Jun 19, 2007
  11. breach

    breach Member

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    So do I undersand correctly. Do you have to use HDMI to get the uncompressed PCM sound?
     
  12. error5

    error5 Regular member

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    Since we're in the HD DVD section I'll try to discuss how to get lossless sound from the current players. Practically all lossless sound from HD DVD discs are in the form of Dolby True HD soundtracks. The few discs out there that have DTS-HD Master Audio are usually EU imports.

    All HD DVD standalone players can decode Dolby True HD soundtracks. There are two ways to enjoy Dolby True HD:

    1. HDMI

    All the current 1st and 2nd generation standalone HD DVD players can use this connection. The player extracts the Dolby TrueHD soundtrack from the disc. This signal is then decoded and mixed in multichannel (uncompressed) PCM. This can be transmitted through HDMI version 1.1 or better. If you use this method you have to ensure that your receiver not only has an HDMI input but should also have the ability to handle the multichannel PCM signal. Some receivers have HDMI inputs but ignore the audio signal and act only as switchers - i.e. the Pioneer 1016tx.

    2. 5.1 Analog Connections

    The following standalone players have 5.1 line-level analog outputs: HD-A1, HD-XA1, HD-XA2. In this case the player again extracts the Dolby TrueHD soundtrack from the disc which then undergoes decoding and mixing to uncompressed PCM. This multichannel signal then goes thrugh a digital to analog conversion before being transmitted through the 5.1 analog connections. You can use any receiver with 5.1 analog inputs to enjoy Dolby True HD.

    So to answer your question, you can use HDMI if your receiver knows how to handle the full multichannel PCM signal. Otherwise you can use 5.1 analog connections if your HD DVD player is the A1, XA1 or the XA2.

    Anyone please correct me or add anything relevant.
     
  13. dblbogey7

    dblbogey7 Guest

    I think you've got it covered error5. Did we miss anything Ced or eatsushi?

    I think we clarified this a few weeks ago with an update.

    The XA2 could get bitstream transmission capability with a future FW update. It has the SIL Vastline 9134 HDMI 1.3 chip which supports advanced audio codec transmission. The only problem will be discs authored in advanced mode which will require a mechanism to bypass default player decoding.

    The PS3 has an HDMI 1.3 transmitter chip that doesn't support advanced audio codec transmission. It's the SIL Vastline 9132 Gaming Transmitter.


     

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