[sdiy] Unstability of oscillators and psychoacoustic qualitie s

[Gene Stopp]

I remember the "Tau" VCO kits from CFR back in the 70's... in their
documentation they went out of their way to detail their "warm" sound as
resulting from slight noise modulation of the sawtooth reset theshold -
graphs and everything. Back at the time I remember thinking that either they
were on to something or they were trying to rationalize the behavior of
something they couldn't do anything about ("it's not a bug, it's a
feature!"). Anybody have a copy of their datasheet?

- Gene

Gene Stopp

-----Original Message-----
From: jhaible [mailto:jhaible at debitel.net]
Sent: Tuesday, September 24, 2002 12:36 AM
To: Magnus Danielson
Cc: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Unstability of oscillators and psychoacoustic
qualities


>We have already learned something important and I haven't even started
>measuring anything!!!

That's always a good thing, *especially* with synths.
It's quite impossible for me to make any serious measurments
on a working synth, because I always end up playing it rather
than making scientific measurements.
That's the good thing about theory (and simulation) - paper
and spice don't distract us that way.

>I have to some degree avoided the use of the term "fat" in these
discussions.

What is the difference between "warm" and "fat" for you?

(It's all just words, so I guess there is nothing such as right or wrong
here.
Just curious how you use the words. BTW, when I switch the modulation
off on the Lambda Strings - bringing them to a locked condition
immediately -
I like to call that sound "thin" rather than "cold". This "thin" sound makes
a
wonderful source for further processing with a resinant phaser, too.)


>My point is that I think the issue has not been as clear to designers other
>than "I guess it is a good thing to keep it down" and not "I need to keep
>thermal noise to this leverl to make a warm (or cold) oscillator". I think
>there is a high risc of afterconstruction, thus assuming that certain
thoughts
>where in place even when they where not.

My opinion exactly.

We can only speculate (or ask the designers!). But I'm pretty sure that
it was not intentional on 1st generation synthesizers in the 70's.
I think Yamaha and Korg used linear VCOs because they wanted to avoid
expo converters, not because they calculated that there would be a pleasant
low frequency mistracking from remaining offset voltage, for instance.
And I remember Bob Moog said the noisy PSU was a lucky accident
to prevent the Minimoog VCOs from locking.

JH.