[sdiy] Moogey jitter & drift

[Kenneth Elhardt]

scottnoanh writes:
>>However, this sample proves to me, at least in comparison to a rock-solid
'perfect' digitally generated waveform, there is a *definite* audible
difference.<<

First of all, back when I originally posted the file, only one other person
thought he could hear a difference, but only through his speakers.  He
couldn't hear a difference through headphones.  Nobody else could hear a
difference.  So I quite often see an overexaggeration when somebody says
their is a definite difference.  Especailly when what difference they're
hearing never seems to be specified.  Difference in loudness, or brightness?
Those don't matter, because those have nothing to do with jitter.  I
filtered the digitally perfect waveform with a very subtle 6db filter just
to dull it down slightly to more closely match the Moog, so there is a
slight difference in the upper harmonics.

As far as visually, yes you will see a difference because the way the
44.1KHz sample rate lines up with a slightly jittering and drifting
waveform, will look different than a perfect set of numbers that always hit
the same points every cycle.  You don't see such an obvious difference when
looking at an analog waveform on a scope.  Digitizing seems to make it look
more random in amplitude.

However, to address some of the other talk, this isn't about comparing the
Moog to a digitally perfect waveform anyway.  It's about somebody making
claims that the Moog VCO is somehow significally different than all the
other ANALOG VCOs in the world because the Moog has more jitter.  Nobody had
ever measured it up to that point, that's why I did, and when compared to a
modern stable VCO like the Technosaurus, the Moog had about 3x less jitter.
If more jitter is good, than the Moog must be lousy.  It should have been
case closed on the jitter thing at that point, but some people don't like
their myths shot down with actual numbers.  All analog waveforms have jitter
and drift and other stuff in there.  It's not some exclusive Moog thing.

The longer term drift was even an earlier debate, and I showed how a
completely random drift could be patched up if you didn't think your VCO had
enough of it.  But it got to such points of ridiculousness, that a certain
person tried to maintain that there was something inherently magical when
the pitch of a VCO got to it's present frequency do to change in temperature
as opposed to a change in control voltage, and that the temperture of the
room needs to be taken into account, and that there wasn't a definition for
the word "random", and all kinds of idiocy.  Many VA synths have random
drift settings for their VCO's.  Nothing magical.  A 100Hz sawtooth sounds
the same whether it drifted their by temperature or was pushed their with a
control voltage.

And then Kevin moved on to other things, like power supply noise, and RF
interference, and started bringing up the Sage synth hoax, and if I couldn't
fool 100% of everybody with my 3D rendering, then how could I possibly say
anything about a Moog waveform.  So for him not to be a hypocrite, he better
show measurements for RF interference, power supply noise, room temperature
(not that those have ever been defining characteristics of the sound of a
synth), and he better model and render a 3D synth so real that it fools all
people who see it, otherwise he too can't say anything about a Moog
waveform.

If he wants to show what makes a Moog sound like a Moog, he needs to look at
the whole sound chain in the synth.  The VCO is the least of it.  Almost all
of my different modular VCOs sound identical even if the synth as a whole
sounds different.  He needs to first put up a sample of a Moog sound and one
from a comparison synth so first we can hear the difference, agree what the
difference is, and then look for it.  All his goofy Moog vco stuff means
nothing.  Great, he sees jitter, or drift.  So?  Now what?  We still don't
know what makes a Moog sound like a Moog.

-Elhardt