Matching Frequency mod for Filter and frequency shifter

I have a cool thing going with a Bandpass filter and shifting the signal down at the same frequency on the frequency shifter, but can't work out how to modulate both knobs so that I don't have to do it manually. Any math I can use?


  • Hi!

    There's not much to it except that filter cutoff mod follows the same " .125 factor" per octave rule.

  • Hmmm, that seems close but not all the way there. In this example they are already not aligned.

    basically when knob is at full 1, both the frequency shifter and the cutoff frequency should be at 14756, and at -1, the they should both be at 8.18 hz., and at 0 position, the cutoff and frequency knob should be of equal value as well. Maybe there is some additional scaling to be done.

  • I maybe haven't explained it right. I want the two frequency knobs to match each other across the entire range between them (8.18 hz to 14756hz).

  • edited January 4

    you want the filter to match the frequency of the pitch shifted signal ?


    one is fundamental pitch the other is spectrum content ... not much will be left over to hear ;)

    however, its all gonna depend on what "range" = "how many hz do we shift the fundamental (and the rest)" is set to ...

    fundamental pitch doubles up an octave up (a 220hz, octave up is a440 ... octave up/down is double/half the frequency)

    there is no such frequency relation with the filtered spectrum ... so you need to math that up ;)

    not sure if possible, I suck at math, and its not really meant to do that ... ;)

    hope this helps

    there are a few variables here

    a) what fundamental note is sent to f shifter

    b) how is f shift set up

    f-shift not following the double frequency rule compared to pitch shift - is the whole gag about f-shift ;)

    its not meant to do that 😀

  • I’m just concerned with how the knobs work in this case. The sound is actually really interesting (to my ears) especially at higher frequencies, even more so with atonal inputs as opposed to melodic inputs. Great for taking drums and getting something new out of them. The band pass obviously isn’t a brick wall slope so there is actually a lot of other frequency content that gets transformed down. If you boost the signal it’s a lot more interesting as well.

  • edited January 5

    ah atonal like a drum loop or something, that makes more sense

    what makes the f-shift sonically interesting is

    that it shifts the harmonics unrelated to chromatic scale

    f shift was done before proper pitch shift was invented ...

    (you can pitch drums with f shift without changing the lengh of sound (!) - this heavily changes the frequency content (harmonics) as its shifted linear and doesn't double with the octave, thats why it sounds hm unusual - speeding tape up or down behaves very different)

    what you would need to do is listen to fundamental output pitch of f shift (lowest frequency) (🤯 not possible?)

    and adjust filter frequency accordingly ...

    as the input pitch isnt defined - you can send anything into the f shift like drums.

  • edited January 5

    maybe messing with the pitch detector after the f-shift to control filter?

    otherwise there is no way to tell what the basic pitch is you want to connect the filter frequency to ...

  • edited January 5

    @bcrichards Have you tried a simple offset?

    If that doesn't work then I would say that the most sane solution for matching the "Range" and "Cutoff" scales would be to let @giku align them in the first place. In other words, extend the max value of the F.Shifter Range to 19233Hz and extend the min value of the filters down to 1.17Hz.

    But would that make sense? I'm not sure.

    Mind you, the frequencies are shifted in a linear fashion which means that the relations between harmonics will be destroyed as soon as you start shifting them, and it also means that the shift amount or "Range" naturally won't apply to the shifted harmonics, plus they depend on your input signal.

  • Interesting discussion. Wouldn’t the freq.shift range be non-linear? So both filter and f.shift meet at -1 and +1 extremes, but NOT at the middle 0

    not without some scaling that I expect to involve exp or log

  • I'll keep playing with it - thanks guys!

  • edited January 6

    The “CV to Freq” module does the exponential CV to linear frequency conversion, and can be used for this kind of tracking. But it needs scaling, because the output is the frequency in Hertz and very likely too high: For example an A3 on the CV input will give you 440 at the output.

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