FIRGenLowpass

Computes lowpass FIR filter coefficients.

Syntax

IppStatus ippsFIRGenLowpass_64f(Ipp64f rFreq, Ipp64f* taps, int tapsLen, IppWinType winType, IppBool doNormal);

Parameters

rFreq	Normalized cutoff frequency, must be in the range (0, 0.5).
pTaps	Pointer to the array where computed tap values are stored. The number of elements in the array is tapsLen.
tapsLen	Number of elements in the array containing the tap values; must be equal or greater than 5.
winType	Specifies what type of window is used in computations. The winType must have one of the following values:
	ippWinBartlett Bartlett window;
	ippWinBlackman Blackman window;
	ippWinHamming Hamming window;
	ippWinHann Hann window.
doNormal	Specifies normalized or non-normalized sequence of the filter coefficients is computed. The doNormal must have one of the following values:
	ippTrue The function computes normalized sequence of coefficients.
	ippFalse The function computes non-normalized sequence of coefficients.

Description

The function ippsFIRGenLowpass is declared in the ipps.h file. This function computes tapsLen coefficients for lowpass FIR filter with the cutoff frequency rFreq by windowing the ideal infinite filter coefficients. The parameter winType specifies the type of the window. For more information on window types used by the function, see Windowing Functions. The computed coefficients are stored in the array pTaps.

The example below shows how the function ippsFIRGenLowpass can be used.

Return Values

ippStsNoErr	Indicates no error.
ippStsNullPtrErr	Indicates an error when the pTaps pointer is NULL.
ippStsSizeErr	Indicates an error when the tapsLen is less than 5, or rFreq is out of range.

Using the Function ippsFIRGenLowpass

void func_firgenlowpass()

    int len = 512;

    Ipp64f pDst[512];

    Ipp64f magn = 4095;

    Ipp64f rFreq = 0.2;

    int tapslen = 27;

    int numIters = 512;

    IppsFIRState_64f* pState;

    IppStatus st;

    Ipp64f* FIRDst = ippsMalloc_64f(512*sizeof(Ipp64f));

    Ipp64f* taps = ippsMalloc_64f(tapslen*sizeof(Ipp64f));

    Ipp64f* pDL = ippsMalloc_64f(tapslen*sizeof(Ipp64f));

    ippsZero_64f(pDL,tapslen);

    //generate source vector

    ippsVectorJaehne_64f(pDst, len, magn);// create a Jaehne vector

    //computes tapsLen coefficients for lowpass FIR filter

    ippsFIRGenLowpass_64f(rFreq, taps, tapslen, ippWinBartlett, ippTrue);

    ippsFIRInitAlloc_64f(&pState, taps,tapslen, pDL);

    //filter an input vector

    ippsFIR_64f(pDst, FIRDst, numIters, pState);

Result: