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Noise modulation and subjective performance of DACs

Posted 25th December 2012 at 04:22 AM by abraxalito
Updated 25th March 2014 at 07:44 AM by abraxalito

I've recently come to the view that the best metric of SQ in DACs is noise modulation, however as yet I'm unclear how best to go about making the measurement. Stereophile tried, and here's what they did - Noise, Modulation, & Digital/Analog Conversion | Stereophile.com

Robert Harley reports no correlation with listening so I deduce from this that the test method isn't looking for the right thing. My own gut feel is we need a multitone test waveform rather than a single sinewave as a sinewave has a crest factor quite unlike music and if a sine provoked the condition we'd see it on the 'N' part of a THD+N vs level test.

Having said that, of course we do indeed see something weird going on - on Weiss Medea's implementation of the ESS Sabre. The THD+N plot versus level shows kinks which most certainly are not increased THD at various levels, so can only be noise floor modulation. See a critique I made on WBF here - http://www.whatsbestforum.com/showth...l=1#post133677

Anyone have any ideas?

Update - someone on Head-Fi just posted up this FFT of the output of an ESS9018 with two different levels of stimulus. Cyan is -35dB, blue is 1dB lower at -36dB. Can you spot any noise modulation?
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  1. Old Comment
    There is something there, the ML 30 is the best DAC I've heard, what's the biggest difference between analog and digital? The noise floor is several orders of magnitude "different" than digital.

    I think the right dithering plays apart in this (note the ML30has a Pacific Microsonics filter, those guys were experts with DAC & ADC.

    Its why we need a good computer to R2R implementation so we can try programs like signalyst to do our over sampling/filtering/dithering and decide with our ears.
    permalink
    Posted 28th December 2012 at 11:26 AM by regal regal is offline
  2. Old Comment
    fas42's Avatar
    The noise floor on digital is excellent, as recorded; the trouble is that it gets mangled on replay. So, dithering has absolutely nothing to do with it, it's all about sorting out the issues mucking up the sound while it's being reproduced.

    If your ears can hear a difference, then there is pretty savage distortion taking place - dynamic distortion! Conventional static measurements of distortion in digital replay have about 0.01% value, meaning, in assessing what actually happens during replay - can be completely disregarded ...

    Frank
    permalink
    Posted 28th December 2012 at 10:23 PM by fas42 fas42 is online now
  3. Old Comment
    abraxalito's Avatar
    The trouble with digital is that there's not a 'floor' for the noise, its a noise elevator - that is unless the ADC is SAR type, correctly dithered.
    permalink
    Posted 29th December 2012 at 09:11 AM by abraxalito abraxalito is offline
  4. Old Comment
    fas42's Avatar
    There's a noise, or distortion, elevator in digital for sure, but it is purely an implementation problem, not a design issue. What is very fortunate for the legacy of recorded music, is that in the majority of cases refining of the implementation of the playback side sorts out most issues; and then for the last bits and pieces very powerful processing algorithms chewing away at what has been captured in digital form will salvage, reverse damage done, to generate a version subjectively satisfying ...

    As an example of the latter, early digital recorders were bad mouthed by audio people for introducing severe phase shifts. Knowing the characteristics of particular units, DSP can perfectly, transparently, unshift the phase "damage" to satisfy those sensitive to such factors.

    Frank
    permalink
    Posted 29th December 2012 at 09:59 AM by fas42 fas42 is online now
    Updated 29th December 2012 at 10:08 AM by fas42
 
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