rtf_create_filter man page

rtf_create_filter — Creates a custom filter


#include <rtfilter.h>

hfilter rtf_create_filter(unsigned int nchann, int proctype,
unsigned int num_len, const void *num,
unsigned int denum_len, const void *denum,
int type);


This function creates and initializes a digital linear filter whose the Z-transform is rational and processing nchann channels of a data type specified by proctype.

The numerator and denominator of the rational expression are specified by respectively two arrays num and denum containing the coefficients in the ascending order of the 2 polynoms. The number of elements in each arrays is controlled by num_len and enum_len. denum_len is allowed to be equal to zero as well as denum is allowed to be NULL. In such case, the denominator will be set to 1. The data type of the values in num and denum are specified by type.

The proctype and type must be one the following constants:

RTF_FLOAT specifies real single precision (float)

RTF_DOUBLE specifies real double precision (double)

RTF_CFLOAT specifies complex single precision (complex float)

RTF_CDOUBLE specifies complex double precision (complex double)

The expected data type of the output of the filter has the same precision as the one specified by proctype and is complex proctype or type specifies a complex type. Said otherwise:

If proctype is RTF_FLOAT or RTF_CFLOAT then the output data type will have single precision. Otherwise it will have double precision.
If proctype or type specifies a complex type, then the output will be complex as well. Otherwise, it will be real.

rtf_create_filter() can be used to use a filter that has been designed somewhere else. In particular, this function can be used directly with the output of filter design function of MATLAB. In such case, the usual B and A arrays returned by the filter design functions corresponds exactly to respectively num and denum.

Return Value

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

Performance Consideration

See note of rtf_filter(3)

See Also

rtf_destroy_filter(3), rtf_init_filter(3), rtf_filter(3)

Referenced By

rtf_create_bandpass_analytic(3), rtf_create_chebychev(3), rtf_create_downsampler(3), rtf_create_fir_lowpass(3), rtf_destroy_filter(3), rtf_filter(3), rtf_get_type(3), rtf_init_filter(3).

2010 EPFL rtfilter library