On 3/3/16 7:23 PM, robert bristow-johnson wrote:
6. another form to consider is the Lattice or, if you're doing it in fixed-point, the Normalized Ladder form. these are all second-order so they all have the same transfer function and you can calculate coefficients as a function of Cookbook coefs or from emulating an analog circuit with trapezoid-integration or Euler's forward method or Euler's backward method or predictor-corrector or whatever source of your heart's desire. so you can have Andrew's or Hal's or Andy Moorer's or Stanley Whites or harris-Brooking's or Massie's or Regalia-Mitra's or whatever definition of a second-order IIR filter you like.
forgot to mention Orfanidis's and Knud Christenson's coefficient definitions...
that is an orthogonal issue. but, if you really wanna crank on the knobs (perhaps with an LFO for tremolo/vibrato), i would do this with a Lattice filter because it decouples the Q from one of the pole coefficients (k2) which means it depends only on the resonant frequency. there is an LPF output tap and an APF output tap and a tap in between (dunno what i would call it) and you can combine those three taps in any arbitrary way and get any arbitrary numerator to your biquad transfer function. but i think that the slewing/stabilty behavior of a Lattice is better than that of any other filter topology that i have tried.
-- r b-j r...@audioimagination.com "Imagination is more important than knowledge." _______________________________________________ dupswapdrop: music-dsp mailing list music-dsp@music.columbia.edu https://lists.columbia.edu/mailman/listinfo/music-dsp
