Remove interpolation of IIR filter coefficients #1345
Conversation
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Very good to see you are already trying to put this into Fluidsynth. I'm not sure what IIR means or what that does to the filter. And I know even less on what fres_mod changes to the cutoff frequency but I'm sure you got this down to a tee. As you can tell, at this point I'm pretty much lost on what all this means but glad you were able to find the issue and stop anymore clicks and pops to the sound as well. Wow this seems like it will not be easy to find what is behind the problem at all then. Sure, on stuff like this it will be your call to do what you assume is the best way forward. So you had to remove it. I just listened to both samples and find it hard to hear that much of difference, in other words, to me each sample has clicks and pops, but the second has barely any less, why is that ? |
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You need to listen till the end. The first clicks appear in DF2.ogg after 22 sec. |
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Yes I'm able to hear the clicks in DF2.ogg but also get clicks in DF2-nointerp.ogg as well |
During implementation of #1342, I found the IIR filter producing strange cracks and clicks. I haven't done a deep investigation but it seems that this was caused by big and frequent changes of the cutoff frequency by
fres_mod.I found that the clicks were produced by the code that interpolates the filter coefficients. I.e. setting
if(dsp_filter_coeff_incr_count > 0)toif(FALSE)didn't cause any more clicks.Without a deeper investigation of the numeric logic I don't know how to fix this. Yet, I don't think this justifies the more complex logic, and therefore I'm suggesting to remove that interpolation logic.
Attached is a ZIP with two audio samples. DF2.ogg (Direct Form 2) is the filter as implemented before this PR. DF2-nointerp.ogg is the same filter without any interpolation.
filter-coeff-interp.zip