[sdiy] oscillator jitter / phase noise

[Magnus Danielson]

From: "Cornutt, David K" <david.k.cornutt at boeing.com>
Subject: RE: [sdiy] oscillator jitter / phase noise
Date: Tue, 8 Jun 2004 16:06:44 -0500
Message-ID: <F2907359F3D3E246843DDCA786665653025E706F at xch-se-01.se.nos.boeing.com>

David,

> 
> From: Magnus Danielson [mailto:cfmd at bredband.net]
> > 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.
> 
> Magnus, please explain a bit more.  I'm not sure I follow this...
> 
> > 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.
> 
> Hmmm.  If phase modulation is really a form of FM, then it seems
> to follow from this that digital recording can't accurately
> reproduce a frequency-modulated waveform.  But I'm sure that
> isn't what you said.

You are correct, it is not what I meant.

To make things correctly, frequency modulation is a form of phase modulation,
not the other way around.

> What is the "harder to retrieve" form?
> Are you talking about interpolating between samples?  There's
> something I'm not understanding here.

What I'm saying is that interpolating from samples is simply not really
cutting it, especially since each sample isn't really taken at a real equi-
distance from each other, but also has jitter in it. Processing and filtering
done in the sampling process will help to introduce dispersion, which causes
signal dependency jitter on a small time scale which doesn't affect the
acoustical sound much, but spoils the values for measurement. Oversampling
with noise-shaping even further stresses this detail. Just analysing how these
impairments affects the measurement is as such a quite a difficult task. Then
one needs to analyse the waveform in order to better predict the impairments
and then compensate for it. For me it sound much simpler just to build a
time interval counter with sufficient resolution, it's not that hard IMHO.

See my point now?

So, what would be people's reference phat sound? How would you prefer I setup
my MiniMoog which I just got (mint condition, new oscillator board).

Cheers,
Magnus