NAME

       rtf_create_chebychev, rtf_create_butterworth - Creates IIR Chebychev and Butterwoth filters

SYNOPSIS

       #include <rtf_common.h>

       hfilter rtf_create_chebychev(unsigned int nchann, int proctype,
                                    double fc, unsigned int num_pole,
                                    int highpass, double r);
       hfilter rtf_create_butterworth(unsigned int nchann, int proctype,
                                      double fc, unsigned int num_pole,
                                      int highpass);

DESCRIPTION

       rtf_create_chebychev()  creates  a IIR chebychev filter processing nchann channels of data type specified
       by proctype with fc as normalized cutoff frequency, whose the Z-transform has num_pole  poles  and  whose
       the  impulse  response  has  a  ripple  of  r This latter is expressed as the ratio between the overshoot
       (difference between the max value of the response to a unit step and the unit length) and the unit length
       (ratio not expressed in decibels).

       rtf_create_butterworth()  is the same as rtf_create_chebychev() but creates a butterworth filter (which a
       special case of a chebychev filter with a ripple of 0).

       A normalized frequency is the ratio between the absolute frequency and the  sampling  frequency  (i.e.  a
       value of 1.0 refers to the sampling frequency).

       If  highpass  is 0, it specifies the filter should be a lowpass. If highpass is non-zero, the should be a
       highpass.

RETURN VALUE

       Returns the handle to the created filter in case of success, NULL otherwise.

SEE ALSO

       rtf_create_filter(3), rtf_destroy_filter(3)