"10 bit/54 MHz vs. 12 bit/108 MHz" Video DAC

Discussion in 'Archived Threads 2001-2004' started by EnzoP, Jun 28, 2002.

  1. EnzoP

    EnzoP Auditioning

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    I tried to search for a comparison of these 2 different D/A converters but had no luck. Could someone please lead me to a place that can explain to me what exactly the difference is? or maybe a place that can explain what D/A converters do. thanks.
     
  2. TravisMc

    TravisMc Stunt Coordinator

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    Enzo,

    I might be wrong here.....but generally, what i think it does is where a 56Mhz DAC scans the DVD signal 2 times, a 108Mhz DAC Scans it 4 times

    I recently bought a Sony 715P DVD player, which sports a 108Mhz DAC, and what sony calls, "Four times super scan" or something to that effect

    Basically, its for a clearer picture, But you would be VERY hard pressed to see a difference between 56Mhz Models and 108Mhz model IMHO

    -Travis
     
  3. John Kotches

    John Kotches Cinematographer

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    Guys,

    I am by no means an expert on this topic.... But here's my take. Others with greater expertise are welcome to chime in.

    A D/A convertor takes a digital input and turns it into an analog signal (usually voltage).

    The number of bits limits the resolution.

    The speed discusses the maximum input sampling rate.

    The D/A convertors receive the output of the MPEG decoder, which outputs PCM data @8-bit depth for conversion by the DAC.

    Some DACs do 2x and 4x oversampling, why? There's an output filter which is used to smooth the output so that you no longer have a stepped square wave, but rather a smooth wave more closely resembling a Sine.

    As for the bits... I believe the MPEG output is 8-bit data, with the 9th used for control. Greater than 9-bits are so that the linearity of the lower bits is maintained. Perhaps I am wrong on this.

    One other thing, a poorly implemented 12bit/108MHz DAC can perform worse than a 10bit/54MHz DAC.

    This is the tip of the iceberg, speaking from a technical basis.

    Regards,
     
  4. Micahel C

    Micahel C Stunt Coordinator

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    John, I'd assume that there's a price consideration here as well although I could be wrong. The newly announced Pioneer Universal players show that the DV-47Ai like it's predecessor the 47A, will have the 12bit/108 MHz DAC while it's new "little brother", the 45A will employ the 10 bit/54 MHz DAC. Price difference around $500.00 retail.
     
  5. John Kotches

    John Kotches Cinematographer

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    Micahel,

    I'm not sure what the parts costs differential is between the 10bit/54MHz and 12bit/108MHz parts.

    On the audio side, the cost differential is negligible.

    Regards,
     

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