NAME

butter - Find butterworth filter


SYNOPSIS

 call butter(hilo,cutoff,npoly,num,den)


INPUT PARAMETERS

hilo - real
      >0 low-pass, <0 high-pass
cutoff - real
      cut-off frequency
npoly - integer
      number of poly


OUTPUT PARAMETERS

num- real(npoly)
       numerator
den - real(npoly)
       denominator


DESCRIPTION

 Find the numerator and denominator Z-transforms of the Butterworth filter.
 hilo={1.,-1.} for {low,high}-pass filter
 cutoff in Nyquist units, i.e. cutoff=1 for (1,-1,1,-1...)


SEE ALSO

Bandpass


LIBRARY

sepfilterf90