Bw_CascadeCoef
Advanced Analysis Library Only
AnalysisLibErrType Bw_CascadeCoef (double samplingFrequency, double lowerCutoffFreq, double upperCutoffFreq, IIRFilterPtr filterInformation);
Purpose
Generates the set of cascade form filter coefficients to implement an IIR filter as specified by the Butterworth 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 Bw_CascadeCoef.
If the type and order remain the same, you can call Bw_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 Code
/* Design a cascade lowpass Butterworth 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) {
Bw_CascadeCoef(fs, fl, fh, filterInfo);
IIRCascadeFiltering(x, n, filterInfo, y);
FreeIIRFilterPtr(filterInfo);
}
Parameters
| Input | ||
| Name | Type | Description |
| samplingFrequency | double | The sampling frequency in Hertz. |
| lowerCutoffFreq | double | The lower cutoff frequency of the filter in Hertz. |
| upperCutoffFreq | double | 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. |
Additional Information
Library: Advanced Analysis Library
Include file: analysis.h
LabWindows/CVI compatibility: LabWindows/CVI 4.0 and later
Example
Refer to analysis\iirfiltr.cws for an example of using the Bw_CascadeCoef function.