CxIIRCascadeFiltering
Advanced Analysis Library Only
AnalysisLibErrType CxIIRCascadeFiltering (NIComplexNumber xArray[], ssize_t numberOfElements, IIRFilterPtr filterInformation, CxIIRFilterStatePtr filterState, NIComplexNumber yArray[]);
Purpose
Filters the complex input sequence using the cascade IIR filter specified by the filterInformation structure. Each of the IIR cascaded stages is second order for lowpass and highpass filters, and fourth order for bandpass and bandstop filters.
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 and then calling one of the cascade IIR design functions before you call CxIIRCascadeFiltering.
The filterInformation structure contains the internal filter state information for the filtering operation so you can call CxIIRCascadeFiltering in a loop to continually filter new input array data and produce new output filtered data.
If you finish filtering one set of input data and want to filter a completely new data set, call ResetIIRFilter before you call CxIIRCascadeFiltering with the new data. ResetIIRFilter causes the internal filter state information to clear before the next filtering operation.
Example Code
/* Generate a random complex signal and filter it using a designed cascade lowpass Butterworth IIR filter. */
NIComplexNumber x[256], y[256];
double input[256];
double fs, fc;
int type, order;
ssize_t n;
IIRFilterPtr filterInfo = NULL;
CxIIRFilterStatePtr state = NULL;
n = 256;
fs = 1000.0;
fc = 200.0;
order = 5;
type = LOWPASS;
WhiteNoise (n, 1, 17, input);
for(int i = 0; i < n; i++){
x[i].real = input[i];
x[i].imaginary = input[i];
}
filterInfo = AllocIIRFilterPtr(type, order);
state = AllocCxIIRFilterStatePtr(type, order);
if(filterInfo != 0 && state != 0) {
Bw_CascadeCoef(fs, fc, 0.0, filterInfo);
CxIIRCascadeFiltering(x, n, filterInfo, state, y);
FreeIIRFilterPtr(filterInfo);
FreeCxIIRFilterStatePtr(state);
}
Parameters
| Input | ||
| Name | Type | Description |
| xArray | NIComplexNumber [] | Array that contains the raw data to filter. |
| numberOfElements | ssize_t | The number of points in both the input and output arrays. |
| 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 and then calling one of the cascade IIR design functions before calling this function. |
| filterState | CxIIRFilterStatePtr | Pointer to the filter structure that contains the internal filter information. You must allocate this structure by calling AllocCxIIRFilterStatePtr and free this structure by calling FreeCxIIRFilterStatePtr. |
| Output | ||
| Name | Type | Description |
| yArray | NIComplexNumber [] | Array that contains the output of the IIR filtering operation. The size of this array must be at least numberOfElements. |
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 2012 and later