# rtf_create_chebychev man page

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

## Referenced By

rtf_create_butterworth(3) is an alias of rtf_create_chebychev(3).