[sdiy] Re: Variable Waveshape LFO

[François CHAUVET]

Don Tillman wrote:

>The two-diodes-and-a pot in the VCO core approach works well, but that
>isn't voltage controlled and may have a slight detuning effect on the
>pitch. So that's good for LFO's with manual control.

>You could do a voltage controlled version of that, with OTA's
>replacing the pot, but there would be a much greater effect on the
>pitch. So that's okay for LFO's with voltage controlled waveshape.

A "slight" detuning effect? I did that about 20 years ago, and detuning was
well over one octave! Be it with two diodes & a pot, or with OTAs...

>My approach is a post-processor on a sawtooth wave, which is a little
>more work, but it's voltage controlled and is guaranteed not to affect
>the pitch. So that's good for audio VCO's with voltage controlled
>waveshape.

This is exactly the technique I use. Pitch is not affected at all, but I
still have an enormous glitch at the reset of the (reference) sawtooth wave.
This can however be filtered out, but  the waveshape's "corners" are a bit
"rounded". No real problem for an audio VCO, but might be (a bit) disturbing
when using it as a LFO... although I can't really see what the problem would
exactly be (this is supposed to be a musical synth, not an analog computer,
after all).

-- françois


-- 
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.432 / Virus Database: 268.16.10/624 - Release Date: 12/01/2007
14:04