Hi List,<br><br>I have a working duplicate of GGEE&#39;s [lowpass] in purepd, and have noticed an interesting  thing on my setup here.  GGEE&#39;s [lowpass] seems to be sharp by a semitone or so, while the purepd impl produces coefficients which are in tune with a osc~ at the same frequency.  This is very obvious when using small bandwidth values.  I&#39;ve verified my omega, alpha, and a0-a2, b0-b2 values against GGEE&#39;s lowpass.h/lowpass.c as correct and a perl script doing the same calculations.<br>
<br>The attached .ogg file shows the ggee coefficients in a biquad~ with noise~ running through it, a purepd [lowpass], and then a pure osc~ at the same cuttoff frequency.  It switches between the ggee, purepd, and the osc.  The attached .pd file can be used to reproduce the behavior.<br>
<br>Can you reproduce this behavior on your machine?  GGEE&#39;s code appears legit, so I suspect the issues some place else (like samplerate, etc).<br><br>Cheers!<br>~brandon<br>