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Re: you missed out on my last paragraph

Posted by Christine Tham (R) on November 24, 2005 at 21:52:08

In Reply to: Re: you missed out on my last paragraph posted by JamesB on November 24, 2005 at 21:05:25:

*** When you mentioned "ultrasonic noise present in DSD", I thought you were talking about the rise in HF noise that results from the 1 bit noise shaping, the noise that players have filters designed to cut to prevent downstream components having problems, not converter noise. ***

It's actually the same thing. Again, read the application notes from BB and CL. A typical PCM sigma delta ADC does noise shaping on the 1 bit modulated signal, resulting in an ultrasonic noise curve very similar to DSD (I think the latest BB app note even have figures of theoretical curve vs actual measured curve).

*** Every comparison I read between DVDA and SACD talks of the ultrasonic noise of DSD as against the linear response of PCM, is this not the case, or are you talking about something different? ***

PCM derived from a sigma delta ADC does NOT have a linear response. Check actual response curves of real world ADCs, they are NOT flat, because the ultrasonic noise have been filtered away. And if the ultrasonic noise is NOT filtered, then PCM will also have the same noise characteristics as DSD.

PS - Ultrasonic noise is also generated by delta sigma DACs. Again, check real world response curves of actual DVD-Audio players - typically they are NOT flat above 20kHz. For example, on my panasonic DVD-S97, the response is down -0.5dB at 20kHz and rapidly declines after that - again, this is to offset out of band noise generated by the DAC. Hopefully you'll see the actual curve once I publish the review of that player (along with a review of a modded Marantz DV-6500 - that one has an even steeper curve)

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