FIRGen

Generates finite filter coefficients by windowing infinite filter coefficients. The low-pass, high-pass, band-pass, and band-stop filter coefficients are supported. The supported windows are the Bartlett window, Blackman window, Hamming window, and Hann window.

This function computes the len coefficients h(n) for the FIR filter with the cutoff frequency freq(F) by converting ideal infinite filter coefficients hd(n) via windowing window(n).

The main formula is as follows: $\text{[math]}$ .

For details about windowing, see the HMPP windowing functions.

$\text{[math]}$ .

The formula for the low-pass time domain is as follows:

The formula for the high-pass time domain is as follows:

The formula for the band-pass time domain is as follows:

The formula for the band-stop time domain is as follows:

The normalization formula for the low-pass time domain is as follows:

The normalization formula for the high-pass time domain is as follows:

The normalization formula for the band-pass time domain is as follows:

The normalization formula for the band-stop time domain is as follows:

The FIRGen function calling process is as follows:

Initialize the buffer by calling Init.
Call the main function.
Release the buffer by calling Release.

The function interface is declared as follows:

Initialization:
HmppResult HMPPS_FIRGenInit_64f(int32_t tapsLen, uint8_t **buffer);
Main functions:
HmppResult HMPPS_FIRGenLowpass_64f(double freq, double *taps, int32_t tapsLen, HmppWinType winType, HmppBool doNormal, uint8_t *buffer);

HmppResult HMPPS_FIRGenHighpass_64f(double freq, double *taps, int32_t tapsLen, HmppWinType winType, HmppBool doNormal, uint8_t *buffer);

HmppResult HMPPS_FIRGenBandpass_64f(double freqLow, double freqHigh, double *taps, int32_t tapsLen, HmppWinType winType, HmppBool doNormal, uint8_t *buffer);

HmppResult HMPPS_FIRGenBandstop_64f(double freqLow, double freqHigh, double *taps, int32_t tapsLen, HmppWinType winType, HmppBool doNormal, uint8_t *buffer);
Memory release:
HmppResult HMPPS_FIRGenRelease(uint8_t *buffer);

Parameters

Parameter	Description	Value Range	Input/Output
tapsLen	Length of the finite filter coefficient	[5, INT_MAX]	Input
freq	Cut-off frequency	(0, 0.5)	Input
freqLow	Low cut-off frequency	(0, 0.5) and less than the value of freqHigh	Input
freqHigh	High cut-off frequency	(0, 0.5) and greater than the value of freqLow	Input
taps	Pointer to the vector that stores calculated tap values	The value cannot be NULL.	Output
winType	Window type used in the computation	HMPP_WIN_BARTLETT, HMPP_WIN_BLACKMAN, HMPP_WIN_HAMMING, or HMPP_WIN_HANN	Input
doNormal	Whether to normalize filter coefficients	HMPP_TRUE or HMPP_FALSE	Input
buffer (in the Init function)	Pointer to the memory that stores the pointer to the buffer	The value cannot be NULL.	Output
buffer (in the main and release functions)	Pointer to the buffer	The value cannot be NULL.	Input

Return Value

Success: HMPP_STS_NO_ERR
Failure: An error code is returned.

Error Codes

Error Code	Description
HMPP_STS_NO_ERR	No error occurs.
HMPP_STS_NULL_PTR_ERR	Any of the specified pointers is NULL.
HMPP_STS_SIZE_ERR	tapsLen < 5 freq ≤ 0, or freq ≥ 0.5 freqLow or freqHigh ≤ 0, freqLow or freqHigh ≥ 0.5, freqLow ≥ freqHigh
HMPP_STS_WIN_TYPE_ERR	The window type is incorrect.
HMPP_STS_OVERFLOW	The function overflows.
HMPP_STS_MALLOC_FAILED	The Init function failed to allocate the memory required by the algorithm model.

Note

Before this interface is called for calculation, the Init interface must be called to initialize the buffer standard structure.
After the buffer structure has been initialized, if a main function fails to be executed, the Release function must be used to release the buffer structure.

Example

#define TPAS_LEN_S 8
void FIRGenBandpassExample(void)
{
    int32_t tapsLen = TPAS_LEN_S;
    double freqLow = 0.05;
    double freqHigh = 0.48;
    HmppWinType winType = HMPP_WIN_BARTLETT;
    HmppBool doNormal = HMPP_TRUE;
    double taps[TPAS_LEN_S] = { 0.0 };

    uint8_t *buffer = NULL;
    HmppResult result;

    result = HMPPS_FIRGenInit_64f(tapsLen, &buffer);
    printf("HMPPS_FIRGenInit_64f result = %d\n", result);
    if (result != HMPP_STS_NO_ERR) {
        return;
    }
    result = HMPPS_FIRGenBandpass_64f(freqLow, freqHigh, taps, tapsLen, winType, doNormal, buffer);
    printf("HMPPS_FIRGenBandpass_64f result = %d\n", result);
    HMPPS_FIRGenRelease(buffer);
    buffer = NULL;
    if (result != HMPP_STS_NO_ERR) {
        return;
    }

    int32_t i;
    printf("tapsLen = %d\ntaps =", tapsLen);
    for(i = 0; i < tapsLen; ++i){
        printf(" %f", taps[i]);
    }
    printf("\n");
}

Output:

HMPPS_FIRGenInit_64f result = 0
HMPPS_FIRGenBandpass_64f result = 0
tapsLen = 8
taps = -0.000000 0.010000 -0.196259 0.517494 0.517494 -0.196259 0.010000 -0.000000

Parent topic: Filtering Algorithms