[sdiy] jitter, warmth, and so on

[John Mahoney]

Detailed examination of VCOs is very much in line with the purposes 
of the synth-DIY group, so I hope that the arguments about the value 
of "dissecting" oscillators are done. (There's probably a correlation 
between heated threads like that and the number of "unsubscribe" 
messages, although that is merely a hypothesis of mine.)

Regarding VCOs, are we merely exploring the area of jitter, or are we 
looking for something in particular? Examining jitter isn't 
necessarily a bad thing, but do we know if it's a worthwhile pursuit? So...

I'm pretty sure that this has been mentioned before, in one form or 
another, but I'll suggest it again. Let's:
	1) Assemble a set of audio files containing sound samples of various 
oscillators.
	2) See if we can collectively identify the audible differences of 
them. (A blind test, preferably.)
	3) Try to correlate the electrical and sonic characteristics.

Does that make sense? If so, we need to start with:
	0) Establish a standard format for the audio samples. Say, 24-bits, 
44.1K or 96K sampling rate, and audio frequencies of 55, 220, 880, 
and 1760 Hz (A in various octaves). WAV files, not MP3, right? (Oh... 
Should the audio frequencies be factors of 44100 so the wavelengths 
are whole numbers of samples? At least, programmatically generated 
waves can be such.)

The issues of differences in preamps, sound cards, and A/D converters 
should not be too important, because our study will be based on the 
differences (audible and otherwise) in the recorded samples. It will 
be important to match the signal levels of the samples, but that's 
about it. If a recorded sound has a bunch of jitter from the ADC, 
we'll [theoretically] hear it, and we'll see it in the measurements; 
although we won't know the source of that jitter, I'm not convinced 
that we need to know. It won't hurt to have the same oscs sampled by 
multiple people.

As things progress, we can use tricks such as taking single cycles 
from certain oscs and looping them, in order to preserve unique 
waveshapes while removing jitter. I believe that this technique has 
been used already (by Elhardt) but I'm not sure.

David Cornutt used Csound (as I recall) to generate waves with 
certain characteristics, and this will also be a very useful technique.

Ideally, one person could record all the samples, but it's unlikely 
that any of us has access to enough different VCOs to make it worthwhile.

I'll be glad to host the sample files, if we can get this together. I 
can also make a few samples: Synthesizers.com, Korg Mono/Poly 
(SSM2033), Moogerfooger (within frequency limits, since it's 
ostensibly an LFO), OB-X, and a digital keyboard or two.

In short, let's *find* the best sounds first -- if we can! -- and 
then try to find the essential aspects of them. (I know, people 
thought an A6 was a Minimoog, and I don't care. Let's move on!)

Then again, maybe the premise is that Moog oscs sound great, so let's 
see what makes them sound that way. I guess that I'm saying we should 
toss out that premise.

This is probably a silly idea. Having already typed it all out, 
though, I'm hitting the send button!
--
john