.\"Copyright 2010 (c) EPFL
.TH RTF_CREATE_CHEBYCHEV 3 2010 "EPFL" "rtfilter library"
.SH NAME
rtf_create_chebychev, rtf_create_butterworth
- Creates IIR Chebychev and Butterwoth filters
.SH SYNOPSIS
.LP
.B #include <rtf_common.h>
.sp
.BI "hfilter rtf_create_chebychev(unsigned int " nchann ", int " proctype ","
.br
.BI "                             double " fc ", unsigned int " num_pole ","
.br
.BI "                             int " highpass ", double " r ");"
.br
.BI "hfilter rtf_create_butterworth(unsigned int " nchann ", int " proctype ","
.br
.BI "                               double " fc ", unsigned int " num_pole ","
.br
.BI "                               int " highpass ");"
.br
.SH DESCRIPTION
.LP
\fBrtf_create_chebychev\fP() creates a IIR chebychev filter processing
\fInchann\fP channels of data type specified by \fIproctype\fP with
\fIfc\fP as normalized cutoff frequency, whose the Z-transform has
\fInum_pole\fP poles and whose the impulse response has a ripple of \fIr\fP
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 \fBnot\fP expressed in decibels).
.LP
\fBrtf_create_butterworth\fP() is the same as \fBrtf_create_chebychev\fP()
but creates a butterworth filter (which a special case of a chebychev filter
with a ripple of 0).
.LP
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).
.LP
If \fIhighpass\fP is 0, it specifies the filter should be a lowpass. If
\fIhighpass\fP is non-zero, the should be a highpass.
.SH "RETURN VALUE"
.LP
Returns the handle to the created filter in case of success, NULL otherwise.
.SH "SEE ALSO"
.BR rtf_create_filter (3),
.BR rtf_destroy_filter (3)