[sdiy] VCO jitter, Slop ... (was: Re: Smith's Evolver Desktop's spikey VCO waveforms)

cheater00 . cheater00 at gmail.com
Tue Jun 11 15:28:50 CEST 2013

Hi Brian,

On Mon, Jun 10, 2013 at 10:15 AM,  <rsdio at sounds.wa.com> wrote:
> I disagree with your hypothesis (Michael?), that analog VCOs sound better or
> fatter due to jitter. My hypothesis would be exactly the opposite. Based on
> many other circuits, I'd say that digital clocks, oscillators, and PLLs are far
> more susceptible to jitter than analog VCOs and PLLs. In fact, the fix for
> jitter in a digital system is to create an analog PLL with a presumably analog
> VCO to smooth out the jitter of the digital, crystal-based clock.

> If anything, it's the lack of jitter in an analog system that probably makes it
> sound fatter than a DCO. If jitter made a VCO sound better, then we could
> fatten up any CD by letting the jitter run out of control.

I think the difference here is that DCO jitter is closely coupled to
the state of the DCO and therefore to the signal that's jittering.
That means the two signals are correlated. On the other hand
modulating a VCO with analogue noise means complete lack of
correlation. I don't know how to exactly do this, but if I were to
test this hypothesis - whether or not the spectrum of correlation (a
generalization of correlation coefficient) matters - then I'd
phase-modulate a perfect waveform with noise with different spectra of
correlation with the original signal.


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