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.