The functions described in this section initialize an infinite impulse response (IIR) filter and perform filtering. Intel IPP supports two types of filters: arbitrary order filter and biquad filter.
The figure below shows the structure of an arbitrary order IIR filter.
Here x[n] is a sample of the input signal, y[n] is a sample of the output signal, order is the filter order, and b0, b1, . . ., b order, a1, . . ., a order are the reduced filter coefficients.
The output signal is computed by the following formula:
.
Reduced coefficients are calculated as ak = Ak/A0 and bk = Bk/A0
where A0, A 1,...Aorder, B0, B1,...Border are initial filter coefficients (taps).
A biquad IIR filter is a cascade of second-order filters. Figure below illustrates the structure of the biquad filter with k cascades of second-order filters.
To initialize and use an IIR filter, follow this general scheme:
- Call ippsIIRInitAlloc to allocate memory and initialize the filter as an arbitrary order IIR filter, or call ippsIIRInitAlloc_BiQuad to allocate memory and initialize the filter as a cascade of biquads. Or alternatively call ippsIIRInit to initialize the filter as an arbitrary order IIR filter in the external buffer, or ippsIIRInit_BiQuad to initialize the filter as a cascade of biquads in the external buffer. Size of the buffer can be computed by calling the functions ippsIIRGetStateSize or ippsIIRGetStateSize_BiQuad, respectively.
- Call ippsIIROnerepeatedly to filter a single sample through an IIR filter or call ippsIIR to filter consecutive samples at once.
- Call ippsIIRGetDlyLine and ippsIIRSetDlyLine to get and set the delay line values in the IIR state structure.
- Call ippsIIRSetTaps to set new tap values in the previously initialized filter state structure.
- After all filtering is complete, call ippsIIRFree to release dynamic memory associated with the filter state structure created by ippsIIRInitAlloc or ippsIIRInitAlloc_BiQuad.
Alternatively, you may use the direct version of the functions. These functions perform filtering without initializing the filter state structure. All required parameters are directly set in the function.