Filter bandwidth in octaves

Dear all

BPF is doing my head in with its RQ, so I need a bit of help if anyone understands. After a few searches I found that the bandwidth in the RQ equations is in Hertz, and trying to convert from a bandwidth in octaves seems to not yield what I would expect…

I take the formula here to convert between octave and q, which works for me in other environments.

I’m certain I’m wrong, since I found no post on this subject, but maybe someone knows how to convert filter bandwidths in octaves to rQ…


edit: Obviously, BBandPass would do the job I reckon. I don’t seem to get the same behaviour… I’ll investigate more.

final update, I was fighting a lost fight:

  • I found a bug and will report to the github repo. Once the filters are exploded, they never recover. I presume the NaN is polluting that channel, and one needs to restart the

  • stemming from that I was blowing my filters and got crazy not understanding why things were moving but not sounding.

  • SOS (and therefore BBandPass) compute differently so I get a lot less problem there than with BPF. I presume the latter does not like crazy modulation that much before blowing all over.

So all in all, I hope this post helps anyone who is trying to get filters to behave with quick jittery modulation. I might post the github bug link so anyone could see if that was fixed.

Further info, thanks to @muellmusik - the ‘bug’ is just a filter generating NaNs which is the expected behaviour… and that crashes the channel in the internal audio driver of the MacOS… so very little to do with SC. is my new friend.