Sorry I was unclear in my original email. This is separate from the amplitude envelope.. I’m talking about a modulating envelope that’s only connected to the resonant frequency of the filter.. it shifts it by about 1-semitone over the course of 1 second or so..
Sent from my iPhone > On Apr 26, 2023, at 1:07 AM, Andy Farnell <[email protected]> wrote: > > 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?
