-
Make a VCO
-
Plug the sawtooth output into a VCF
-
Set the VCF’s frequency, resonance and drive all to min
-
Plug the VCF’s HPF output into a Scope
-
Plug the original wave coming from the VCO into the same Scope
-
Compare!
It seems like with filter frequency at min, the HPF of a moderate frequency wave should look similar to that wave. But no! Try different kind of waves and see. My favorite is what happens to a digital square wave, but all waves are affected, even sines.
Is this known?
(Note that LPF doesn’t have the symmetrical problem. With the filter’s frequency at max, the LPF of a moderate frequency wave is always very similar to that wave.)
Background: I’m trying to match a cello sustain sound by passing a sawtooth wave through a bunch of VCF’s plugged into a mixer. Naively I assumed that with the default VCF settings, LPF+HPF=IN and the whole thing can work as an equalizer. But instead it noticeably reduces volume and cuts high frequencies. I narrowed it down to the HPF problem above. For a cello sound in particular, the frequencies affected by the problem are very noticeable and important.