# rtf_create_fir_lowpass - Man Page

Creates FIR lowpass, highpass and bandpass windowed sinc filters

## Synopsis

**#include <rtf_common.h>**

**hfilter rtf_create_fir_lowpass(unsigned int** *nch***, int** *proctype***,**

**double** *fc***, unsigned int** *hlen***,**

**KernelWindow** *wndtype***);****hfilter rtf_create_fir_highpass(unsigned int** *nch***, int** *proctype***,**

**double** *fc***, unsigned int** *hlen***,**

**KernelWindow** *wndtype***);****hfilter rtf_create_fir_bandpass(unsigned int** *nchann***, int** *proctype***,**

**double** *fc_low***, double** *fc_high***,**

**unsigned int** *hlen***,**

**KernelWindow** *wndtype***);**

## Description

**rtf_create_fir_lowpass**() creates a lowpass windowed sinc filter processing *nchann* channels of data type specified by *proctype* with *fc* as normalized cutoff frequency and *hlen* as the half length of the window.

**rtf_create_fir_highpass**() is the same as **rtf_create_fir_lowpass**() but creates a highpass filter.

**rtf_create_fir_bandpass**() is the same but creates a bandpass filter with *fc_low* and *fc_high* as respectively the lowpass and highpass normalized cutoff frequencies.

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).

The parameter *proctype* has the same meaning as in rtf_create_filter(3). Refers to its manpage for more details.

The parameter *wndtype* specifies the type of window applied to the impulse response and can take the following values: **BLACKMAN_WINDOW**, **HAMMING_WINDOW** or **RECT_WINDOW** (see a book on signal processing for details about their meaning).

## Return Value

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

## See Also

## Referenced By

The man pages rtf_create_fir_bandpass(3) and rtf_create_fir_highpass(3) are aliases of rtf_create_fir_lowpass(3).