[Harry van Haaren]
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.
>How is the "rise time" determined here?
As a function of the filter's damping (zeta = 2*Q) and frequency:
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