RTF_CREATE_DOWNSAMPLER(3) rtfilter library RTF_CREATE_DOWNSAMPLER(3)NAME
rtf_create_downsampler - Creates downsampling filter
SYNOPSIS
#include <rtfilter.h>
hfilter rtf_create_downsampler(unsigned int nch, int type,
unsigned int r);
DESCRIPTION
rtf_create_downsampler() creates a filter that downsamples signals coming from nch channels of type type (see rtf_create_filter(3)) by a
decimation factor of r (i.e. the sampling frequency of the input will be r times the sampling frequency of the output). This is achieved
internally by applying a lowpass 4-order Chebychev filter to the input data using a normalized cutoff frequency of 0.8/(2*r) and decimating
the result every r samples.
RETURN VALUE
Returns the handle to the created filter in case of success, NULL otherwise.
NOTES
On the contrary of most other filters, the number of samples returned by rtf_filter(3) is different than the input (as expected) but also
may vary at each call if the number of sample supplied in input is not a multiple of r.
SEE ALSO rtf_filter(3), rtf_create_filter(3), rtf_destroy_filter(3)EPFL 2010 RTF_CREATE_DOWNSAMPLER(3)
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RTF_CREATE_CHEBYCHEV(3) rtfilter library RTF_CREATE_CHEBYCHEV(3)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_destroy_filter(3)EPFL 2010 RTF_CREATE_CHEBYCHEV(3)