---
name: "rtf_create_chebychev"
section: "3"
platform: "linux"
package: "librtfilter-dev"
version: "1.1-4+b3"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/rtf_create_chebychev"
---

# rtf\_create\_chebychev(3)

Creates IIR Chebychev and Butterwoth filters

## 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_create_filter/3.md), [**rtf\_destroy\_filter**(3)](/rtf_destroy_filter/3.md)