Re: Dirty Digital [sic.]

In article <sMadnWiTJvwU9_rVnZ2dnUVZ_jydnZ2d@xxxxxxxxxxx>, Arny
Krueger
<arnyk@xxxxxxxxxx> wrote:
"Jim Lesurf" <noise@xxxxxxxxxxxxxxx> wrote in message
news:4fb66c918dnoise@xxxxxxxxxxxxxxx

I find it hard to fathom why he persistently follows the same muddled
line of his articles over many years. But I suspect that it stems from
a 'cart before horse' thought process. This starts with his belief
that CD inherently and unavoidably has the alleged 'hard grey sound'
and then jumping onto what he reports as the 'reason'. Alas, that
approach seems classic with some people in audio. Founded on a faith
held as certainty, then 'factoids' are assembled to provide
(unreliable) 'support'. Shame.

John Atkinson has held tight to his practice of using undithered tones
to test digital equipment over in SP.

Well, I can see that using undithered waveforms makes sense for some
purposes. Also that when the signal level approaches 0dBFS the quantisation
as a percentage will be fairly small.

But I'd worry about it when trying to assess the 'distortion' performance
of something like a CD Player. The fundamental problem in information
theory terms is that the test waveform is *not* a sinusoid, but some other
'near-sinusoidal' waveform whose details vary with choice of nominal
frequency, amplitude, and phase. In effect, you are running a curious sort
of intermodulation distortion test, whose details you may not understand.

The snag then becomes that - even if your analysis avoids the quantisation
created components - using others to measure player nonlinarity doesn't
establish the result means anything when the input signal is any other
wavform shape. if you don't correctly understand the input, how can you
decide what consitutes a meaningful measure of 'distortion' for any other
circumstances? THD as traditionally defined, it isn't.

One of the points of dither (as distinct from its close relation, noise
shaping) here is - as I think John Phillips pointed out - to decorrelate
the quantisation effects out of the measurement. So getting the ability to
find the specific effects of nonlinearity on the deterministic part of the
waveform, and use statistics to reduce other effects.

Slainte,

Jim

--
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Electronics http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
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.

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