Thank you, Spencer. It's still going to take me a bit to catch up with the math.
For a SawOsc at 220.0 Hz through a BRF at 880.0 Hz Q has rather interesting behavior between 0.01 and 0.03, cuts out at 0.04, and then doesn't seem to change much between 0.05 and 1.0. I made a nearly-impossible-to-read screencast here http://youtu.be/Z3uBNUfvih4 And sorry, no sound. I should learn how to use internets someday. michael On Mon, Oct 27, 2014 at 5:24 PM, Spencer Salazar <[email protected]> wrote: > Hey Mike, > > I usually assume that mathematically Q = f / Δf and this hasn't gotten me in > trouble yet, but I am not a real audio engineering guy so maybe this could > be false in some cases. > > In ChucK's case, for brf, the code looks like this: > [...] > // set_brf > inline void set_brf( t_CKFLOAT freq, t_CKFLOAT Q ) > { > t_CKFLOAT pfreq = freq * g_radians_per_sample; > t_CKFLOAT pbw = 1.0 / Q * pfreq * .5; > [...] > > so in that last line, Δω = ω/(2Q), so Q = ω/(2Δω) = f/(2Δf). I don't know > for sure if the extra 2 in the denominator is a scaling factor or actually > part of the Q-bandwidth relationship for this filter. I would be surprised > if it was the latter though given the "standard" definition of Q one sees, > given above. > > I can see how it would be confusing because the term Q is also used for the > LPF and HPF filters as resonance, which is the gain of the peak at the > cutoff frequency, in which case the f/Δf relation is not correct or even > applicable. > > spencer > > > On Mon, Oct 27, 2014 at 12:34 PM, Michael Heuer <[email protected]> wrote: >> >> Hello, >> >> I'm currently using the C*APS Eq10 10-band equalizer >> >> http://quitte.de/dsp/caps.html#CAPS_for_Electric_Guitar >> >> via the LADSPA ChuGin >> >> https://github.com/jwmatthys/chugins >> >> as part of an effect but all I really need is something to scoop the >> mids. I thought I might use the BRF band reject filter >> >> http://chuck.cs.princeton.edu/doc/program/ugen_full.html#BRF >> >> I can't tell how to set the bandwidth (or described another way, the >> range of frequencies around the center frequency that are rejected by >> the filter). I went off into reading Miller Puckette's book Theory >> and Techniques of Electronic Music >> >> http://msp.ucsd.edu/techniques.htm >> >> and am now lost somewhere in the imaginary plane. >> >> The definition of the Q parameter seems to vary among the different >> ChucK filters (resonance vs quality vs Q) and I suppose I should >> understand what that means. Feel free to tell me to go back to my >> reading. :) >> >> michael >> _______________________________________________ >> chuck-users mailing list >> [email protected] >> https://lists.cs.princeton.edu/mailman/listinfo/chuck-users >> >> > > > _______________________________________________ > chuck-users mailing list > [email protected] > https://lists.cs.princeton.edu/mailman/listinfo/chuck-users > _______________________________________________ chuck-users mailing list [email protected] https://lists.cs.princeton.edu/mailman/listinfo/chuck-users
