Cheby Cheby Cheby.

Theo t.hogers at
Fri Mar 31 18:47:50 CEST 2000

Yhea, the idea is a VCF with vowel like character.
There are other ways to do this, as you pointed out.
A formant resonant filter with a few mod's will do the job.
(the res. filter was a kind of boast only parametric eq., it can be mod. to
CV controlled sweep)
Don't know the MOTM or MAM units, suppose they look like the formant thing.

The point is that the circuit becomes quite bulky if you go that way.
A Cheby with exstreamly "bad" behaviour should make a far more simple unit.
I'am going to do a DSP implementation first, (that is not as hard as you
might exspect).
When the sonic results are what I hope for, its time for a analog version.

I'am not sure if it is possible to build a CV controlled filter that keeps
its Cheby character when
the cutoff freq. is swept. Maybe some of the hardcore analog filter masters
have a opinion on that?
For now point of departure is a state variable VCF design.
If it all works out it will be included in the Q-o-matic, a kind of anti
tank device
to kill of mutants and other M-F#$%ers. (actualy I like the moog part, but
well u know..)
Schedule for the Q-o-matic is early next year.
The proto already has two 24dB multi-mode VCF's that can be either in
parallel or in series.
The whole Cheby thing would be just another feature to set it apart from the

Cheers Theo.

----- Original Message -----
From: Tony Clark <clark at>
To: <synth-diy at>
Sent: Friday, March 31, 2000 10:37 PM
Subject: Re: My math is crap! talk group.

> > PS: The "exstreme" Chebyshev makes a kind of "vowel" VCF, at least
> > what I hope of it.
> > Don't know if it is even possible to build it.
> > Simulation suggested that 7th order had the right bumps and holes in the
> > frequentie responce.
>    Just curious, are your intentions to make a fixed "vowel" VCF?
> Otherwise, I'd suggest a triple-bandpass filter ala MOTM or MAM, etc.
> And if three ripples aren't enough, just chain another module in
> parallel.  At least then you can sweep the filters to get those true
> vocal-like sounds.
>    And sure, it's quite possible to build them, but if I recall
> correctly, getting the component values "just right" starts getting fun
> after 4-th order.
>    Good luck.
>    Tony
> ------------------------------------,----------------------------------
> I can't drive (my Moog) 55!         |     The E-Music DIY Archive
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