biquad~ coefficient help?
Hi Folks,
Can someone give me a bit of help dealing with the coefficients for [biquad~]?
I’m trying to do the following:
Lowpass @ 3dB/octave
Highpass @ 3dB/octave
Highpass @ 6dB/octave
I realize I can do the 6dB Highpass with [onepole~], but for a variety of reasons, I’d like to do it all with [biquad~]
Thanks!
well, you can do them all with onepole~.
but for biquad just use [filtercoeff~].
How do you do 3dB/octave with onepole~? I though it was fixed at 6dB/octave. As for filtercoef~ and filtergraph~ both, the number I’m struggling with is the Q number. On a lowpass, is Q=1 a -6dB/octave? If so, does that me Q=0.5 is a -3dB/octave? Thanks.
Check out these two equations which turn bandwidth to quality factor and the reverse, hopefully it will help:
Hey Luke, thanks for that! Am I correct in thinking that a bandwidth of 1 means 1 octave and a bandwidth of 2 means 2 octaves? What’s puzzling me is that even when I widen the bandwidth, it seems like the slope is still at 6dB/octave. Perhaps it’s the way [filtergraph~] is drawing it, but it seems that if I set the bandwidth to 2, then it drops a total of 12dB inside that band, and if I set it to 3, it looks like it’s dropping 18dB. Either way–assuming I’m seeing it correctly, which is always a risky assumption–it looks like it is still maintaining a slope of 6dB/octave.
Bandwidth of a filter and the slope are independent of each other. For a brief explanation of slope, have a look at the following link I found: http://www.soundfirst.com/Filter_Slopes.html
Q is a factor of bandwidth and center frequency: http://www.sengpielaudio.com/calculator-bandwidth.htm
Hope this helps!