[sdiy] Filters

[john mahoney]

----- Original Message ----- 
From: "The D.U.G." <dug at dugdesign.com>

> Ok.. I could resist to expose my stupidity.
Ignorance, not stupidity. Just means you don't know something, yet. :-)

> In a VCF.
>
> Does Voltage Controlled just mean that it has a CV input?
Yes, at least one.

> Does the voltage modulate the cutoff freq.?
Usually, the cutoff frequency is the only VC parameter. Some filters also
have VC resonance. It can go beyond that, but rarely does (VC filter mode,
for example).

> Is the voltage requried?
> I.E. What if I want to make a guitar fx pedal?
Most filter fx for guitar use an envelope follower to track the level
("volume") of the guitar signal, so higher output from the guitar increases
the output of the envelope follower, which in turn increases the VCF's
cutoff frequency. There is often a lag control to slow down & smooth out the
envelope follower's response.

When you play a chord on the guitar (for example), it quickly goes from soft
to loud, then slowly gets softer again -- the envelope follower will thus
cause the VCF to open up and then slowly close down, so you hear the filter
sweep up and back down. Again, the lag allows you to reduce the speed at
which the filter opens up.

You can also use an LFO to control the VCF, by itself or in conjuction with
an envelope follower.
--
john