[sdiy] Imperfect VCO

[Scott Gravenhorst]

Harry Bissell Jr <harrybissell at prodigy.net> wrote:
>The ringing effect could be synthesized by a SVF
>in resonance... you could differentiate the saw wave
>(RC hipass filter) to get a single, narrow spike...

You know, this had crossed my mind, but I also figured that
there would be more and more of the ramp passed through as
the frequency increases.  That's why I mentioned using a VCO
that has a built in reset pulse available to trigger the ring
generator.  Thinking again, I can't say using the
differentiator method is a bad thing though (except maybe
when a triangle waveform is to be mangled).

>then feed this to a filter at high resonance to
>generate
>the ringing signal, then add the two back together...
>
>I suspect if the ring frequency is too high, or too
>short in duration... that MC is correct (not audible).

Absolutely agreed, I was thinking more on the lines of
ringing in the 2 to 8 times the VCO frequency range, where it
might be useful in adding harmonics.  Calibrating that might
be tricky.  Then again, other techniques could be used to
make all kinds of interesting repeatable things happen at the
behest of the reset trigger pulse, like a chain of VC oneshots.  

The classic integrator/schmitt trigger triangle VCO also
produces a nice edge at the output of the schmitt trigger
that could be used for this.

>Is it 'worth' it...? let us know your result :^P

Well, it sounds like drawing board and breadboard time.



>--- Scott Gravenhorst <music.maker at gte.net> wrote:
>> 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.
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>> questioned.
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>> 
>> -- 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/
>> 
>

=========================================================  
- 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/