IIR/ SIR Filters

[Debutante]

Hello everyone! Once again , just out for some general info. Would anyone care to elaborate on the differences between these two forms of filtering...what they are designed for, where they are best suited, why you would pick one over the other, personal preferences...anything at all....CHEERS!

[Borogove]

Hello everyone! Once again , just out for some general info. Would anyone care to elaborate on the differences between these two forms of filtering...what they are designed for, where they are best suited, why you would pick one over the other, personal preferences...anything at all....CHEERS!

A very similar question from the developer side came up recently.

SIR (sampled impulse response) filters are, technically, FIR (finite impulse response) filters aka convolution filters.

For FIRs, it's technically straightforward to shape any arbitrary desired frequency response and phase response (pro). However, narrow frequency response features like precise resonant-peak tuning requires very long impulse response, which requires lots of computing power (con). Arbitrary control of phase response (which means delay time) means that FIR can easily do reverb and filtering at the same time, which is great for getting the sound of a particular room (pro).

IIRs correspond directly to analog filter designs, so they're familiar to synthesists (pro). With IIRs, sharp resonant peaks can be precisely tuned, CPU-cheaply (pro). Since it's not technically simple to control phase and frequency response separately, it's hard (though not impossible) to shape a desired reverb effect with IIRs (con).

Mostly, we use IIRs for gross shaping of instrument timbre in subtractive synthesis, and the occasional resonant squlechy noise. Mostly, we use FIRs for precise, complex frequency responses, room simulation, and reverb.

[Stupid American Pig]

BTW Borogrove, how yer modular effect thingy coming along, or are you not doing that anymore?

[Debutante]

Hello everyone! Once again , just out for some general info. Would anyone care to elaborate on the differences between these two forms of filtering...what they are designed for, where they are best suited, why you would pick one over the other, personal preferences...anything at all....CHEERS!

A very similar question from the developer side came up recently.

SIR (sampled impulse response) filters are, technically, FIR (finite impulse response) filters aka convolution filters.

For FIRs, it's technically straightforward to shape any arbitrary desired frequency response and phase response (pro). However, narrow frequency response features like precise resonant-peak tuning requires very long impulse response, which requires lots of computing power (con). Arbitrary control of phase response (which means delay time) means that FIR can easily do reverb and filtering at the same time, which is great for getting the sound of a particular room (pro).

IIRs correspond directly to analog filter designs, so they're familiar to synthesists (pro). With IIRs, sharp resonant peaks can be precisely tuned, CPU-cheaply (pro). Since it's not technically simple to control phase and frequency response separately, it's hard (though not impossible) to shape a desired reverb effect with IIRs (con).

Mostly, we use IIRs for gross shaping of instrument timbre in subtractive synthesis, and the occasional resonant squlechy noise. Mostly, we use FIRs for precise, complex frequency responses, room simulation, and reverb.

...I dare anyone to beat that reply!

[tobybear]

..I dare anyone to beat that reply!

Not trying to beat it, but www.dspguru.com has some more interesting info on this topic in its FAQs:

http://www.dspguru.com/info/faqs/firfaq.htm

http://www.dspguru.com/info/faqs/iirfaq.htm

Cheers

Toby

www.tobybear.de

[Debutante]

...Thanks alot guys!,... and the dspguru site was great. I hope they finish th IIR Faq though...soon

[Borogove]

BTW Borogrove, how yer modular effect thingy coming along, or are you not doing that anymore?

On indefinite hold. I started a comic book.