key follow formula

[Logado]

Can somebody tell formula.
I thought that there just pitch multiplied by the coefficient. But I began to compare realized that there a little more complex.

[tulamide]

Key follow means, that, for example, a filter will adjust its cutoff according to the octave steps from the reference note.
Mostly the reference note is middle C, so if a note plays 1 octave higher (and key follow is at 100%) the filter will open up to double the cutoff frequency.

reference is C3, note played is C4, lowpass is set to 1 kHz, follow key is at 100% --> the filter will open up to 2kHz
reference is C3, note played is C2, lowpass is set to 1 kHz, follow key is at 100% --> the filter will open up to 500 Hz
reference is C3, note played is F#2, lowpass is set to 1 kHz, follow key is at 100% --> the filter will open up to 1.5 kHz

That said, and if pitch is the midi note number, it should work with

cutoff + ((pitch - 60) / 12 * cutoff * fkdepth)

where fkdepth is a percentage value in the range [0, 1], for the strength of the follow key function

[Logado]

thank you, understood

[tulamide]

Hey Logado,

I made a big mistake (that also nobody else seem to have noticed). It leads to the change being made absolute rather than relative!

Here is the corrected, relative version:

Code: Select all

cutoff = 1000      #a cutoff frequency like from a filter
reference = 60.0   #To what midi note does the function refer to (middle c = 60)
pitch = 60.0      #The current pitch as midi note
fkdepth = 1.0      #The strength of the follow-key-function

f = 0.0
oct = (pitch / 12.0) - (reference / 12)

if oct < 0
   f = 1 / (oct.abs * 2)
elsif oct == 0
   f = 1.0
else
   f = oct.abs * 2
end

result = cutoff * (f * fkdepth)

[Logado]

I think it works well now. But if keyfollow set to zero filter is always closed. I need to add сlassic dry/wet mix?

[Nubeat7]

yes if depth is 0% , cutoff knob should set the the filter

why not do all the calculation in the pitch range

so it would be cutoff(pitch) = (pitch - reference)*depth+cutoff(pitch)

and then convert the range from pitch to 0..1

its like in the stock module just that you also subtract the reference octave from the pitch

[Logado]

I'm happy

[tulamide]

Yes, that was a second absolute-relative error I made. Thanks Nubeat, for correcting it

I never saw a key follow funtion in the stock modules. So It was all from my head. Maybe that is an excuse?

[Logado]

Yes, that was a second absolute-relative error I made. Thanks Nubeat, for correcting it

I never saw a key follow funtion in the stock modules. So It was all from my head. Maybe that is an excuse?

Do not worry, you guided me on the right path.

[Nubeat7]

don't mind tulamide, its an interesting thread, i never invested that much thoughts and your explanation makes it very clear i think its also a good thing to do it with a reference octave!