1.4.2.17 DSP_FilterIIRBQ16_parallel8_fast Function

Performs a 8 parallel single-pass IIR Biquad Filters, and sums the result.

Description

int16_t DSP_FilterIIRBQ16_parallel8_fast(int16_t Xin, PARM_EQUAL_FILTER_16 *pFilter);

Calculates a 8 parallel, single pass IIR biquad filters on Xin, sums the result and delivers the result as a 16-bit output. All math is performed using 16 bit instructions, which results rounded to 16-bits for the output. The delay register is stored as a 16-bit value for subsequent functions. Output is tuned by 2 multiplier factors. First each parallel section has a fractional gain (attenuation) that enables individual scaling of that section. Second, a global binary (log2N) gain is applied to the result. The combination of gain factors enable both gain and attenuation. All values are fractional Q15. The function will round outputs and saturate if maximum or minimum values are exceeded.

Y = Y7/8 + Y6/8 + Y5/8 + Y4/8 + Y3/8 + Y2/8 + Y1/8 + Y0/8 where each Yn filter element represents a unique IIR biquad: Yn = X(0)*b0 + (b1 * X(n-1)) + (b2 * X(n-2)) - (a1 * Yn(-1)) - (a2 * Yn(-2))

Preconditions

Delay register values should be initialized to zero. The sum of all fracgain should be <= 1

Parameters

Xin input data element X (int16_t)

pFilter pointer to filter coef and delay structure

Returns

Sample output Y (int16_t)

Remarks

The delay register values should be initialized to zero prior to the first call to the function, they are updated each pass. A gain of 2 has been hard coded into the function. This implies that all coefs should be input at half value. This is purposeful, since many filter designs need a div2 to have each coef between the required -1

Example

PARM_EQUAL_FILTER_16 filtArrayPara[8]; _// note change in data structure_

uint16_t dataY, dataX;

_// fill entire Filter Array with coefs_

for (i=0;i<8;i++)

{

filtArrayPara[i].Z[0]=0;

filtArrayPara[i].Z[1]=0;

filtArrayPara[i].G.fracGain = 0x7FFF; _// gain = 1 default_

filtArrayPara[i].G.expGain = 1; _// log2N; gain of 2_

_// note all coefs are half value of original design, gain handled in algorithm_

_// none pass -- default_

filtArrayPara[i].b[0]=0; _// feed forward b0 coef_

filtArrayPara[i].b[1]=0; _// feed forward b1 coef_

filtArrayPara[i].b[2]=0; _// feed forward b2 coef_

_// note all coefs are half value of original design, gain handled in algorithm_

_// note subtract is handled in algorithm, so coefs go in at actual value_

filtArrayPara[i].a[0]=0; _// feedback a1 coef_

filtArrayPara[i].a[1]=0; _// feedback a2 coef_

}

_// 1K bandpass Q=0.9_

filtArrayPara[7].G.fracGain = 0x4000; _// gain = 0.5 because using 2 outputs_

_// note all coefs are half value of original design, gain handled in algorithm_

filtArrayPara[7].b[0]=0x04ad;

filtArrayPara[7].b[1]=0; _// feed forward b1 coef_

filtArrayPara[7].b[2]=0xfb53; _// feed forward b2 coef_

_// note all coefs are half value of original design, gain handled in algorithm_

_// note subtract is handled in algorithm, so coefs go in at actual value_

filtArrayPara[7].a[0]=0x8a90; _// feedback a1 coef_

filtArrayPara[7].a[1]=0x36a4; _// feedback a2 coef_

_// 300 Hz bandpass Q=0.9_

filtArrayPara[6].G.fracGain = 0x1000; _// gain = 0.125 as an example_

_// note all coefs are half value of original design, gain handled in algorithm_

filtArrayPara[6].b[0]=0x017b; _// feed forward b0 coef_

filtArrayPara[6].b[1]=0; _// feed forward b1 coef_

filtArrayPara[6].b[2]=0xfe85; _// feed forward b2 coef_

_// note all coefs are half value of original design, gain handled in algorithm_

_// note subtract is handled in algorithm, so coefs go in at actual value_

filtArrayPara[6].a[0]=0x8316; _// feedback a1 coef_

filtArrayPara[6].a[1]=0x3d08; _// feedback a2 coef_

for (i=0;i<256;i++)

{

_// *** get input data here_

dataX = compound_300_1K_hz16[i];

dataY = DSP_FilterIIRBQ16_cascade8_fast(dataX, filtArray);

_// *** do something with the DataY here_

}

C

int16_t DSP_FilterIIRBQ16_parallel8_fast (int16_t Xin , PARM_EQUAL_FILTER_16 * pFilter );