[sdiy] filtering cv

[synth at oldmail.charlielamm.com]

On Wed, 14 Jul 2004, gregory zifcak wrote:

> what happens if you patch an analog sequencer through a resonant low-pass 
> filter to the pitch cv input of an oscillator? 

i'm assuming that depending 
> on the cutoff, the change would be slewed, giving a portamento effect. then 
> what happens if you turn up the resonance? what does the change sound like? 
> what about self-oscillation? what would the sequencer output look like?

I will answer your questions with strokes of a broad brush....the group 
may want to refine this answer:

--If the filter is designed to only pass audio ("AC coupled" or equiv) 
your
won't get much of anything out the other end, especially if your sequencer
isn't "stepping" very quickly.

--If the filter is designed to allow DC and equiv control signals to pass
from input to output, the output will generally match the input.

--If the filter is self-osciallating and is creating a sine wave at some
sort of audio frequency (say 30hz to 15K) you are in business.  You can
use this output to frequency modulate your oscillators. In this config,
sometimes the output of the VCO's will be bell-like depending on the
nature of the sine wave coming out of the VCF.  However, your sequencer
control signal won't really effect the output unless you modulate the
filter freq with it, as opposed to just putting the seq output into the
audio input of the filter.

But here is a big caveat.  Some sequencers allow very quick stepping (say
100 to 10K steps each second), making them a rough equivalent of an audio
osciallator.  If this is the case, you should be able to use its output as
you would any audio signal, as far as filtering is concerned.

If you provide more details about what sort of hardware or software you 
are using, offline if you want, I can probably provide more details about 
this.


> 
> sorry for the lack of diy. just suppose they are homebuilt modules:)
> 
> greg
> 
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