I have a slight problem in conjunction with using the Butterworth filters in iemlib (specifically, the lp2~ extern). It seems that if the cutoff frequency is changed for a filter object that has now slew-rate argument (for instantaneous cutoff frequency change), that a click is introduced. I assume that this is an artifact of changing that state variables of the filter.
In my case, this problem surfaced in the use of a patch to implement one voice of a polyphonic instrument - when the voice gets re-used, and the new cutoff frequency is different than the one for the last note that the voice got used for, then I get a click at note onset.
Assuming that this is not a bug in the iem filter code, this leads me to the question of is there a dc-block extern available for PD? I guess for now I could try chaining another low pass filter to try to reduce the click; but from my experiences with Csound and Perry Cook's STK, there is a special type of filter (one pole, one zero I think - but could be wrong) that is used to get rid of DC offset.
Larry
Hi Larry,
I don't know of any general technique by which you can change a filter's characteristics instantaneously without causing clicks in the output. I think the only surefire way to proceed is as in the 35.sampler.poly example in which the voice mutes itself for a very short interval in order to be able to make discontinuous changes. THis causes a short delay in the output, usually 5 milliseconds the way I like to set it.
cheers Miller
On Wed, Nov 28, 2001 at 10:07:08PM -0500, Larry Troxler wrote:
I have a slight problem in conjunction with using the Butterworth filters in iemlib (specifically, the lp2~ extern). It seems that if the cutoff frequency is changed for a filter object that has now slew-rate argument (for instantaneous cutoff frequency change), that a click is introduced. I assume that this is an artifact of changing that state variables of the filter.
In my case, this problem surfaced in the use of a patch to implement one voice of a polyphonic instrument - when the voice gets re-used, and the new cutoff frequency is different than the one for the last note that the voice got used for, then I get a click at note onset.
Assuming that this is not a bug in the iem filter code, this leads me to the question of is there a dc-block extern available for PD? I guess for now I could try chaining another low pass filter to try to reduce the click; but from my experiences with Csound and Perry Cook's STK, there is a special type of filter (one pole, one zero I think - but could be wrong) that is used to get rid of DC offset.
Larry
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Larry Troxler -
Miller Puckette