[PD] biquad~ vs. svf~

Krzysztof Czaja czaja at chopin.edu.pl
Fri Feb 27 14:21:53 CET 2004

hi Tim,

while coding cyclone's filters, I was mainly concerned about
matching impulse responses of msp counterparts (I believe, that
currently most of them match 100% for the entire domain of control
parameters... with svf~, however, there is still some difference at
high Q -- this one is tricky to clone, due to a nonlinear component
thrown into the formula).

In theory, a plain svf performs slightly better than four separate
filters (lowpass, highpass, bandpass, notch).  Cyclone's svf is not
a plain svf, but since it does no oversampling, and calculates
the coefficients once per block, the hope is it does perform well
(although the only test I ever did, apart from checking that it is
useable, was estimating the oversampling costs).

Comparing to the biquad~ internal, svf~ does have an overhead,
obviously -- there is always a price for allowing to control
a filter with signal input (both q and f may be modulated).


Tim Blechmann wrote:
> i'm currently using biquad filters (i'm getting the settings from
> iemlib's lowpass, highpass (...) externals).
> i consider to change my patch to use svf~ from the cyclone library.
> does anyone know, which algorithm is more expensive in terms of cpu
> time? and are there any mayor differences in the characteristics of
> these two filter types?

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