[sdiy] Moog wander

[Magnus Danielson]

From: René Schmitz <uzs159 at uni-bonn.de>
Subject: Re: [sdiy] Moog wander
Date: Sun, 16 Apr 2006 23:24:14 +0200
Message-ID: <4442B5FE.9030402 at uni-bonn.de>

> Its an interesting thought, maybe its bogus but anyway:
> 
> If the triggering circuit of your scope or frequency counter or what 
> ever can't be trusted, then why should we trust the reset circuitry 
> within the VCO?

It is bogus, since the reset circuit within the VCO does contribute to its
character where as the trigger circuit in my counter shall make minimal impact
on my measurement of that character. However, it is not bogus when you start to
think about what we can do about the state of things.

I'm expecting to see AM, PM and FM in there.

Modulation of the trigger point causes both an obvious amplitume modulation
(the sawtooth may charge to a lower or higher voltage) but also to a phase
modulation as (the sawtooth may charge a shorter or longer time, shifting the
phase of that cycle). Gaussian and 1/f AM & PM noise will certainly enter at
the reset circuit. Over in the expo-circuit and integrator we will certainly
see Gaussian and 1/f noise contributing to the FM. What I am curious about is
how gaussian and 1/f noise exponentiated through the expo curcuit is going to
contribute noise-wise.

Whenever I look over longer time intervals (such as 1024 frequency measures
back-to-back with 100 ms inbetween) I clearly see some random walking about
from the Mini (VCO 1 at about 167 Hz) and also a raise in the noise at the
bottom of the frequency scale when looking at the FFT of the frequency
measures (thus FFTing the frequency modulation). I have a longer run going
right now for tau = 1s.

For such long periods will my trigger noise be not my major source of error.

Cheers,
Magnus