19 Mar
2013
19 Mar
'13
4:17 a.m.
[Harry van Haaren]
On Mon, Mar 18, 2013 at 11:45 PM, Fons Adriaensen
<fons(a)linuxaudio.org>wrote;wrote:
[...]
A 2nd-order IIR filter is often called a "biquad"; at musicdsp, look
for that instead. There should also be plenty of formulae for
computing 2nd-order lowpass filter coefficients. Those following
tradition (like RBJ's lovely cookbook at musicdsp) will ask for filter
Q, which is 0.5 for critical damping.
A critically damped
second order lowpass with a rise time of 30 ms or so will eliminate all
audible artefacts. It's very low on CPU and you only need to run it while
the gain is changing.
Although I understand the words & their meaning, I have no idea how to
start implementing such a filter.
I've found a 1st order algorithm on musicdsp: How is the "rise time" determined here?
As a function of the filter's damping (zeta = 2*Q) and frequency:
http://en.wikipedia.org/wiki/Rise_time