Bitstream vs PCM

Discussion in 'AV Receivers' started by dusty, Nov 22, 2003.

  1. dusty

    dusty Agent

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    I am having some confusion with the settings of my audio sources. I have two DVD players, both connected digitally. In the setup of the players, there is option for Dolby Digital to be PCM or Bitstream. When I set it to Bitsream and play a DD source, the red Dolby Digital light appears on my receiver (Onkyo TX-SR501). However the bass response is very weak, if anything. When I put the player in PCM mode, I get a much higher bass response. I'm not sure if there is a problem with my receiver, or if this is expected behavior.

    Another note, I couldnt get ANY bass output when using the Avia calibration disc and Bitstream mode on my DVD player. I changed it to PCM and the room was rattling.

    Thanks,
    Dusty
     
  2. John Garcia

    John Garcia Executive Producer

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    PCM is stereo only, you want bitstream or you are not getting discrete audio.

    What are your receiver settings for your speaker sizes and bass management. Sounds like you have something set incorrectly.
     
  3. JeffHunter

    JeffHunter Stunt Coordinator

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    Dusty,

    have you got a subwoofer yet ? .... basically when your in PCM mode your fronts are proccessing the bass (as well as your sub if you have one). If you don't have a sub set your main fronts to 'large' speaker setting and I don't know how much control you have over the direction of frequencies but if you can direct all sub fequencies to your fronts (if you have no sub) then make sure that is done.
     
  4. dusty

    dusty Agent

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    I have a sub (JBL PB10), and I'm pretty sure the receiver is set up correctly. There are no settings for speaker 'size', but there is a setting for the crossover for the LFE. I have it at 120Hz right now (based on the manuals suggestion). My LCR speakers have the following specifications:

    Sound pressure level: 81 dB/W (1.0m)
    Crossover Frequency: 3.5 kHz
    Frequency Range:
    65 Hz - 22 kHz (-16dB)
    95 Hz - 20 kHz (-10dB)

    They are admittedly cheap speakers. I am still experiencing some confusion on calibrating with the AVIA disc. There are no LFE with the DVD player set to Bitstream for DD.

    There is a setting on my DVD player called PCM Down Conversion. Should this be ON or OFF?

    I'm not sure if its related or not, but some DD signals from my DTV receiver (Sony SAT-A65) are not being output through the receiver. It is connected via a Toslink optical cable. The DTV receiver is setup to output Dolby Digital.

    Any suggestions would be appreciated.

    Thanks!
     
  5. Doug Otte

    Doug Otte Supporting Actor

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    Dusty, I won't go into specifics about your decibel settings, etc.

    I also noticed a difference between digital LFE sound and PCM sound in the woofer. I don't think it necessarily has anything to do w/ the receiver settings. I figure it like this:

    Digital is much cleaner & "drier" sounding: it's actually more accurate to the source material.

    PCM is "boomier" & less musical because the receiver is taking your 2-channel PCM source material & putting the lower frequencies out to the woofer. Because the source material is not digital, it just won't sound as clean.

    Doug
     

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