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Helo, I'm using DSP563xx and want to implement 2nd order low pass butterworth IIR filter (fc=250Hz, fs=48000). I did something (with do loop) but it doesn't work correctly. I think that, there is some problem with coefficients scaling. There is a big difference betwen "b" and "a" coef. b = 1.0e-003 * 0.26165269506589 0.52330539013179 0.26165269506589 a = 1.00000000000000 -1.95372794914078 0.95477455992104 Thanks for any help Jacob

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Dear Jacob, sorry to say, I do not kow what you did exactly (regarding algorithm, filter form (Direct Form II, II, Canonic or whatever)). I guess that you are trying to implement a second order biquad filter structure. To figure out the 'big' difference between "b" (nominator) and "a" denominator coefficients (which all have to be smaller than 1.0 by the way) I give you a link to a Motorola Application Note that unfortunately cannot be found on their actual website: http://www.harmony-central.com/Computer/Programming/fir-iir-filter-app-note.pdf Please study this carefully in order to stay tuned with the theory which is the foundation of what you are trying to do right now. This Application Note helped me a lot when I was in the same situation like you are now some years before. Keep on hacking Christian > Helo, > > I'm using DSP563xx and want to implement 2nd order low pass > butterworth IIR filter (fc=250Hz, fs=48000). I did something (with do > loop) but it doesn't work correctly. I think that, there is some > problem with coefficients scaling. There is a big difference > betwen "b" and "a" coef. > > b = > > 1.0e-003 * > 0.26165269506589 0.52330539013179 0.26165269506589 > > a = 1.00000000000000 -1.95372794914078 0.95477455992104 > > Thanks for any help > > Jacob > _____________________________________ > /groups.php3 -- +++ GMX - Mail, Messaging & more http://www.gmx.net +++ Bitte lächeln! Fotogalerie online mit GMX ohne eigene Homepage!

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