SynthMaker

GreenMaths Volume II - IIR-based system identification

Archive · 2008 1 old post

From the original SynthMaker forum (2004–2014), with its members’ names and dates.

steph_tsf ·

Hello,

I have loved RBJ IIR filters GreenMaths Volume I. Alpha, Omega, Q ..

Now I can design any 2nd order IIR and program it into a SynthMaker Code Module. This goes far beyond plain low pass and high pass. Thanks SynthMaker !

Quite often comes the system identification problem.

Say an existing loudspeaker enclosure. If this is a bass-reflex, one would model it using a 4nd-order IIR as high-pass followed by a 1st-order IIR as lowpass. Then, measuring the phase plot in degrees and measuring the magnitude plot in dB, against frequency in Hertz (lin or log ?). Grabbing something like 32 + 32 points. Then feeding that into an Excel spreadsheet. Specifying a sampling frequency (say 44100 Hz). Having Excel trying to mimic those curves using a 4nd-order IIR as high-pass followed by a 1st-order IIR as lowpass. Minimizing the "error surface" between the real curve and the synthezised curves. Then having Excel delivering the coefficients associated to the numerator and denominators of the two IIRs.

That would be a GreenMaths Volume II - IIR-based system identification. How to start with that ? Already existing somewhere ? Any litterature advised ?

Steph

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