Without time to listen to your example Yisheng I'm just voicing a theoretical/academic take; When it comes to LTI (linear time invariant) systems order doesn't matter. With time variant systems it does.
As a very concrete practical example, I made some "rain" weather FX patches that employ short envelopes into resonant bandpass filters. They are IIR filters and meant to "ring". Placing the filters before the envelopes totally changes the effect, A time invariant FIR filter version would not behave differently, but the desired effect actually comes from the ringing, hence the DSP ordering. When things move very slowly, it tends to matter less. regards, andy On Tue, Apr 25, 2023 at 09:19:02PM -0700, Ariadne Lewis-Towbes wrote: > Hi, > > You won't be able to fade between two filtered blocks of complex > (non-sinusoidal) input to the same effect as modulating an arbitrary single > filter's frequency. That said, when modulating an IIR filter such as a > biquad (as shown in your second email's link), you should not need to > compute the z-transform. You may simply modulate the biquad's parameters > repeatedly, and unless you're doing something unusual with respect to > calculating those parameters, the cost will be relatively low. > > Best, > Ariadne Lewis-Towbes > > On 2023-04-25 20:37, Yisheng Jiang wrote: > >I’m trying to render a note that feed into a IIR filter (2-3 poles) > >whose cutoff frequency following an envelope generator, and it’s not > >possible for me to compute the z-transform parameters every rendering > >block.. > > > >Is it approximately the same to generate two pcm streams with the > >starting and ending cutoff frequencies, then cross fade them to make > >the resultant sound?
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