Bitstream vs PCM

Discussion in 'Archived Threads 2001-2004' started by Saul Schwartz, Jan 16, 2003.

  1. Saul Schwartz

    Saul Schwartz Auditioning

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    On my DVD player under Dolby Digital it has 2 options, Bitstream and PCM. What is the difference between these 2..and which is better?
     
  2. Bob McElfresh

    Bob McElfresh Producer

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    I think by "Bitstream" your player means Dolby Digital Bitstream.
    Short Answer: set it to "Bitstream".
    CD players use a format called "PCM". Some older processors only accept this, or the audiophiles want the un-compressed digital stream. So they pick PCM. It only provides a 2-channel/stereo feature.
    Dolby Digital is a COMPRESSED format but can provide 1-6 separate channels of sound in a digital format. I'm sure your manual somewhere instructs you to use "Bitstream" for Dolby Digital.
    HOW TO TEST:
    Set to Bitstream, and load a DVD. Turn on the receiver to the "DVD" input and you should hear some sound.
    Most DVD menu's are only 2-channel. My Yamaha always says "ProLogic" when the DVD menu is like this.
    Make sure you use a modern/recent movie and if it has a "Audio Setup" feature, be sure to pick the DD5.1 or some such sound track.
    Go to the "Scene Selection" on your DVD and jump right into chapter 2 (This will bypass the opening titles/credits). Watch the face of your receiver when you select chapter 2. Most receivers will change their display to say something like "DD", "Dolby", "Dolby Digital" or a little "Digital" light will come on. This tells you the receiver is picking up a dolby digital bitstream.
    Hope this helps.
     
  3. Saul Schwartz

    Saul Schwartz Auditioning

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    Thanks a bunch.
     
  4. Yee-Ming

    Yee-Ming Producer

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    slightly OT, but this rings a bell...

    about 10 years ago I bought a Philips CD player which touted "bitstream" decoding. at that time, most players were touting stuff like "8X oversampling, 16-bits" etc, which an engineer (student) friend of mine explained meant that the player would read the data off the disc 8 times in 16-bit chunks, to ensure accuracy, before decoding.

    "bitstream" was supposed to be something completely different, where the player would read the next bit and build the analog signal by taking the difference and "adding" it on to the end. in retrospect, it sounds a lot like SACD's DSD today, but obviously this isn't what a 10-year old CD player was literally doing.

    so what exactly was my clunky old "bitstream" CD player doing?

    (apologies if this is rather off topic, but the word "bitstream" just made something go "click" in my head)
     

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