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
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 chuck-users@lists.cs.princeton.edu https://lists.cs.princeton.edu/mailman/listinfo/chuck-users