preenfm Forum

PreenFM => preenfm2 and preenfm3 => Topic started by: widdly on August 26, 2014, 07:19:30 AM

Title: Modulating cutoff for the bandpass filter
Post by: widdly on August 26, 2014, 07:19:30 AM

I cannnot get the bandpass filter cutoff to modulate.  If I create a patch with a LP filter and set a modulation matrix to use P1 to modulate the cutoff it works properly.  When I change the filter type to BP, I cannot seem to move the cutoff using P1.  Anyone else having this problem?  Perhaps I'm missing something.

Title: Re: Modulating cutoff for the bandpass filter
Post by: Xavier on August 26, 2014, 01:45:33 PM

It's a know limitation.
Because changing the BP middle frequency requires several heavy operation, so i didn't want to make it change all the time with a modulator.
I think i'll change that.

Title: Re: Modulating cutoff for the bandpass filter
Post by: widdly on August 26, 2014, 04:16:01 PM

I just had a look at the code.  The LP and HP code is pretty tight.  I wonder if you could change the BP to a LP and HP in series.  Remove the resonance parameter and add a width parameter.  The width would be an offset between the LP cutoff and the HP cutoff.  The Yamaha SY-77 had something like that.

Title: Re: Modulating cutoff for the bandpass filter
Post by: toneburst on August 28, 2014, 05:05:54 PM

The Machinedrum and Monomachine (and possibly other Elektron gear) have a similar setup and cascaded low and high-pass filters.

a|x

Title: Re: Modulating cutoff for the bandpass filter
Post by: toneburst on August 28, 2014, 05:07:29 PM

@widdly it would be a shame not to have resonance on the BP filter, though.

a|x