[sdiy] Imperfect VCO

[Czech Martin]

Well, I can tell you what I did in experiment.

I used a Waldorf Microwave I together with some Atari program
that allows for wave drawing (almost) in real time.
This means a wave has 128 (or was it 256?) samples of 8 bit

So I scetched up a triangle. It sounds like an ideal
triangle, so the steps didnt' bother.
Next I introduced little peaks or notches.
As this happens in real time your can hear the effect
at once.

The outcome was that little nonidealities of the wave form
were not audible. Perhaps a slight difference in a A/B
comparison.

To get something interesting you really have to draw
large distortions of the original curve, the more peaks
and the more pointed, the more audible was the effect.
OTOH, a little plateau at the peak had almost no effect.

This will certainly hold if a saw wave is used.
If a sine wave is used, little "artefacts" can be audible.
We can therefore assume that the partials of saw, tri and sqa
waves mask the introduced "artefacts", so that large
changes in the wave form are needed to make some effect.
OTOH a sine wave has no partials, so no masking and earlier
effects.

Therefore I doubt if the normal imperfections of tri, saw and sqa
waves some VCO cicuits have are audible at all. This applies to the steady
state waveform. Other artefacts like momentary phase/frequency
changes were not observed, therefore I can not tell.

Anyway, with wave distortion or mangling you get static
harmonic waves. Most of these will not make you jump and shout.

If you put two waves into one wave shaper, things get spicier, of
course.

If I drew "resonant" peaks, this has some interesting effect.
You are right to say that the resonances should be not
too high in frequency in order to be audible.

I have the impression that simple circuits like diode clippers
give only minor effects, and the more interesting effects
like "folding" , "resonance" need considerable circuit effort.

There is no free lunch.

So on the bottom line: wave mangling is interesting, but you should
not expect wonders from simple circuits.

Drawing your own waves (you can do this with a lot of computer programs
and any sound card), and then running them in loop mode
will give you a good impression and maybe
save one or the other disappointment or expense.

m.c.




-----Original Message-----
From: Scott Gravenhorst [mailto:music.maker at gte.net]
Sent: Donnerstag, 31. Juli 2003 20:30
To: synth-diy at dropmix.xs4all.nl
Subject: RE: [sdiy] Imperfect VCO


>From that accuracy standpoint, that is why I wanted to start with an
accurate VCO and then do wave shaping instead of trying to create a poor
VCO to get a particular sonic character.  Using waveshaping then allows
one control over the harmonic content without worrying about the VCO going
out of tune.

But I'm mystified by Martin's comment that the ringing artifact will
produce no useful character change.  Does that mean I would be largely
wasting my time to develop a VC ringer?  My practical experience isn't
large enough to determine that on my own.

Ian Fritz <ijfritz at earthlink.net> wrote:
>At 08:45 AM 7/31/2003, Czech Martin wrote:
>>Well, using a state var band pass or low pass with resonance
>>is again filtering. If the poles are too far out, you won't hear
>>the ringing, in spite of the fact that it is clearly visible
>>on the scope.
>>
>>I think high frequent wave oddities like ringing with 100kHz
>>or glitches with 10us width are NOT audible on a saw wave signal.
>>And also not on a tri wave.
>>It might be different on a sine wave...
>>
>>m.c.
>
>Right.  As an aside, I would mention that the main reason for developing 
>oscillators with minimal glitching and ringing is not because of their 
>sonic qualities, but rather to obtain more accurate tracking.
>
>   Ian
>

=========================================================  
- Hydrogen is pointless without solar.
- Good or bad, that which gets rewarded, gets done.
- What good are laws that only lawyers understand?
- The media's credibility should always be questioned.
- Governments do nothing well, save collect taxes.

-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
-- Linux Rex         | RedWebMail by RedStarWare
-- FatMan: home1.gte.net/res0658s/FatMan/
-- NonFatMan: home1.gte.net/res0658s/electronics/