Bessel_CascadeCoef

Advanced Analysis Library Only

AnalysisLibErrType Bessel_CascadeCoef (double samplingFreq, double lowerCutoffFreq, double upperCutoffFreq, IIRFilterPtr filterInformation);

Purpose

Generates the set of cascade form filter coefficients to implement an IIR filter as specified by the Bessel filter model.

filterInformation is the pointer to the filter structure that contains the filter coefficients and the internal filter information. You must allocate this structure by calling AllocIIRFilterPtr before calling this cascade IIR filter design function.

To redesign another filter, first call FreeIIRFilterPtr to free the present filter structure and then call AllocIIRFilterPtr with the new type and order parameters before you call Bessel_CascadeCoef.

If the type and order remain the same, you can call Bessel_CascadeCoef without calling FreeIIRFilterPtr and AllocIIRFilterPtr. In this case, you must properly reset the filtering operation for that structure by calling ResetIIRFilter before the first call to IIRCascadeFiltering.

Example

/* Design a cascade lowpass Bessel IIR filter. */
double fs, fl, fh, x[256], y[256];
int type, order, n;
IIRFilterPtr filterInfo;
n = 256;
fs = 1000.0;
fl = 200.0;
order = 5;
type = 0;            /* lowpass */
Uniform(n, 17, x);
filterInfo = AllocIIRFilterPtr(type, order);
if(filterInfo!=0) {

Bessel_CascadeCoef(fs, fl, fh, filterInfo);
IIRCascadeFiltering(x, n, filterInfo, y);
FreeIIRFilterPtr(filterInfo);

}

Parameters

Input
Name Type Description
samplingFreq double-precision Specifies the sampling frequency in Hertz.
lowerCutoffFreq double-precision The lower cutoff frequency of the filter in Hertz.
upperCutoffFreq double-precision The upper cutoff frequency of the filter in Hertz.
filterInformation IIRFilterPtr Pointer to the filter structure that contains the filter coefficients and the internal filter information.

You must allocate this structure by calling AllocIIRFilterPtr before calling this cascade IIR filter design function.

Return Value

Name Type Description
status AnalysisLibErrType A value that specifies the type of error that occurred. Refer to analysis.h for definitions of these constants.