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normalized filter coefficients


I have been trying to implement tunable biquad
bandpass/bandstop filters using an allpass filter on a
fixed point DSP (TI-54x) and have run into the problem
of the filter going unstable when the z^-1 term goes
over 1.  I am using a direct form II implementation,
but have heard that there is a way to normalize the
coefficients (normalized ladders??) to keep the
coefficients less than 1.  The z^-1 term looks like
B(1+alpha), where B controls center frequency and
alpha controls bandwidth.  I was wondering if anybody
could point me to some documentation regarding this,
online or otherwise?

Student, University of Illinois

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