[LAD] [maybe OT] question regarding the FIL equalizer

Hi LAD, I have a technical question regarding the FIL equalizer (by Fons Adriaensen). The code uses Mitra-Regalia lattice filter (as described in [1]). After reordering things here and there I see it's indeed the case (surprise!). [1] might be hard to get, but there is [2] with a lot of details too, especially for bandwidth. The only remaining point that I don't get is the bandwidth manipulations. [1] uses for its parameter 'a' ('_s2' in FIL) the formula: a = (1 - tan(Omega/2)) / (1 + tan(Omega/2)) 'Omega' being I don't really know what (-3dB notch bandwidth for a gain of 0 maybe, if I read the paper correctly). FIL uses bandwith expressed in octave and does: _s2 = (1-b)/(1+b) with: b = bandwidth * 7 * (f0/fs) / sqrt(gain) ('f0' is the center frequency of the equalizer, 'fs' is the sampling rate) Reading [2] we see the factor 'sqrt(gain)' ('gain' is 'K') that we find in the FIL's formula (specifically the formula for k2 at page 13, after equation (17)). But the "bandwidth * 7 * (f0/fs)" remains a total mistery to me. It seems to be 'gamma' as found in [2], but 'gamma' is way more complicated than what we see in FIL's code. So the questions are: - can someone explain to me what this bandwidth computation means? - how it is derived starting from a bandwidth expressed in octave? - And if we use the notations of [1] and [2] how do we relate it to Omega or the various versions found in [2]? (which one is it by the way? I thought it was the "at the bandedge frequencies the gain is 'gain/2 dB'" one but it's not the case) (I wrote a little program to plot things and as far as my program is correct bandedge frequencies don't have a gain of 'gain/2 dB') Regards, Cédric. [1] P. A. Regalia and S. K. Mitra, “Tunable Digital Frequency Response Equalization Filters,” IEEE Trans. Acoust., Speech, Signal Process., vol. ASSP-35 (1987 Jan.). [2] http://www.musicdsp.org/files/EQ-Coefficients.pdf