Idea for a new PFM3 FX auto filter

[matrix12x]

I was recently playing with a Korg Triton... and one of the FX in the Triton would be great here, the "auto filter."

So, its basically 2 band pass filters where one is hard panned right and has panned left. An LFO modulates the cutoff freq of the first BPF and the same LFO but 180 out of phase modulates the second BPF. LFO waveform is the "random" waveform. resonance/Q is set relatively high (but not self oscillating).

Parameters could be:
LFO Rate
Mix (mixing filtered and unfiltered sound)

How this differs from using the current BPF and modulating that using the existing LFOs is the second BPF being modulated 180 out of phase with the first one for a nice stereo effect and the "mix" parameter. this gives a good amount of motion to pads. In the existing BPF, you can't mix the un filtered sound with the filtered sound.

Thoughts?

I would probably start with the existing BPF code.

[Toltekradiation]

Seems like a cool filter trick,
from the Triton manual, i could not find an "auto filter", but there is an "Auto Wah" filter which seems pretty close.

is that this one ?

edit :
the Triton manual https://cdn.korg.com/us/support/download/files/04d7a63fe4ac088ee33dc5fe89cc04d2.pdf

[Toltekradiation]

got it : Stereo Random Filter, page 192

[matrix12x]

yep thats it exactly.

[matrix12x]

That block diagram for the Stereo Random Filter is exactly what I was thinking about implementing. Maybe the parameters should be 1) phase and 2)mix (wet/dry). I'm not sure why I remembered it as auto filter. 

How would I take the current BPF code and modulate it like in this block diagram? or is it really 2 BPFs (L and R) code wise?

We could use the existing LFO and a mod matrix slot to modulate it.

[Toltekradiation]

ok, here is a first version

it's two bp filters, done in paraphonic mode,
so there is a dry/wet parameter and two params : Spread and Reso
it can be modulated from the matrix.

[matrix12x]

Nice. 
It sounds exactly like I had hoped. I'm going to play with it and do some sound design tomorrow. I'm really excited about this. 

@toltekradiation great job as always!!

[Toltekradiation]

Cool,
yes i like it as well, it give nice textures

i think it may benefit letting some bass go through it,
to give a little more body, like frequencies <150 hz.

i did things like that for the flanger, chorus.

[matrix12x]

After playing for a while, I agree re: bass. I noticed that over the range of the mix parameter, I am always playing under 0.6 or so with this effect or it gets oo thin, which makes sense because it is a BPF.

Question: modulating FX2 parameter 1, modulates spread?
Maybe spread should be hard coded to max, and the parameter should be cutoff freq.

[Toltekradiation]

yes, it needs some clarifications :

in the new version attached, things go like this :

The frequency of the bp filters is (f + spread) and (f - spread) for Left and Right channels, folded around -1, 1
Spread param is now bipolar, so at value 0.5, actual spread = 0

The Spread param is not accessible from the matrix, only from the ui and midi CC
From the matrix, the frequency of the bandpass filters is reachable (= f)


Edit : lowpassed signal now go through.

[matrix12x]

thanks. Playing it now. Sounds even better with the bass. :-)

[Toltekradiation]

there is more than just bass going thru,
finally i went for a soft lowpass version of the input to be mixed with the two bandpass filters.
i think it sounds better balanced this way.

[Toltekradiation]

i found a video that show some example of that Triton fx :
https://www.youtube.com/watch?v=ZasgoU6j7lg

that give me some urge to rework my version !

[matrix12x]

cool video. Yeah, thats the exact sound that inspired this idea.
I look forward to what you come up with next.

[Toltekradiation]

ok, here is a reworked version that may suit better,
there is more resonance as it's 2 poles instead of previously 1.
With modulation, it may sound vocal on some types of sounds !