[sdiy] oscillator jitter / phase noise

[Magnus Danielson]

From: René Schmitz <uzs159 at uni-bonn.de>
Subject: Re: [sdiy] oscillator jitter / phase noise
Date: Fri, 04 Jun 2004 20:29:13 +0200
Message-ID: <40C0BF79.8020909 at uni-bonn.de>

> 
> Hej Magnus et al.,

Hej René,

> > That would be to over-interprent what I was saying. What I mean to say is that
> > it is much harder to retrieve the phase modulation waveform when digitized.
> > It is still encoded in the sampled waveform, but in a form which is harder to
> > retrieve than having the raw waveform into a dedicated instrument.
> 
> What about waveforms that are generated digitally? By what you're saying 
> they would inherently have that difficulty. You would need to find a way 
> to process them, since one of the implicit questions is "why are 
> digitally generated waveforms 'cold'".

Actually it's not directly transferable. When I probe out a waveform from an
analogue synth into a time interval counter, then I have a only the oscillators
and time interval counters stability and time-resolutions to deal with. Going
through an A/D and then a D/A process with associated filters adds a whole
little suite of distorsions of precission in measurements. I don't see what the
benefit would be of taking the detour via sampled waveform. Actually, I think 
we are just loosing time on debating it. Let's do propper measurements the
propper way and let's agree on the audio quality of this and that oscillator
and only THEN we can really discuss what is good and not good ways of transfer
and compare the signal from oscillators, when we agreed on the critical
characteristics and their size, i.e. when we have the knowledge we are trying
to build.

> > The phase modulation is distributed throughout the full cycle, but a high
> > resolution measurement is not possible by simple means as we can do when we
> > have intact through-zero slopes.
> 
> Exactly.

Yes, and when we try to retrieve this distributed phase modulation we get
more dependent on particular waveform properties and we also end up smoothing
the result and thus will part of the modulation be filtered out.

Cheers,
Magnus