1.4.2.14 DSP_FilterIIRBQ16_cascade8_fast Function

Performs a single-sample IIR Biquad Filter as a cascade of 8 series filters.

Description

int16_t DSP_FilterIIRBQ16_cascade8_fast(int16_t Xin, PARM_EQUAL_FILTER_16 *pFilter_Array);

Calculates a single pass IIR biquad cascade filter on Xin, and delivers the result as a 16-bit output. The cascade of filters is 8 unique biquad filters arranged in series such that the output of one is provided as the input to the next. A unique filter coefficient set is provided to each, and 16 bit delay lines are maintained for each. All math is performed using 16 bit instructions, which results rounded to 16-bits for the output. All values are fractional Q15, see data structure for specifics. The function will saturate the output should it exceed maximum or minimum values.

Y = Y7 <- Y6 <- Y5 <- Y4 <- Y3 <- Y2 <- Y1 <- Y0 where each Yn filter element represents a unique IIR biquad: Yn = Y(n-1)*b0 + (b1 * Y(n-2)) + (b2 * Y(n-3)) - (a1 * Yn(-1)) - (a2 * Yn(-2)) and: for Y0; Y(n-1) = Xin(0)

Preconditions

Delay register values should be initialized to zero.

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 a t 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 filtArray[8];

uint16_t dataY, dataX;

_// example to use 2 filter blocks as notch filters_

_// fill entire Filter Array with coefs_

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

{

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

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

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

_// all pass_

filtArray[i].b[0]=0x4000;

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

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

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

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

}

_// Unique filters for example_

_// 10KHz notch filter -- divide coefs by 2_

b0 = 0.5883783602332997

b1 = -0.17124071441396285

b2 = 0.5883783602332997

a1 = -0.17124071441396285

a2 = 0.1767567204665992

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

filtArray[3].b[0]=0x25a7; _// feed forward b0 coef_

filtArray[3].b[1]=0xf508; _// feed forward b1 coef_

filtArray[3].b[2]=0x25a7; _// 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_

filtArray[3].a[0]=0xf508; _// feedback a1 coef_

filtArray[3].a[1]=0x0b4f; _// feedback a2 coef_

_// 1 KHz notch filter -- divide coefs by 2_

b0 = 0.9087554064944908

b1 = -1.7990948352036205

b2 = 0.9087554064944908

a1 = -1.7990948352036205

a2 = 0.8175108129889816

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

filtArray[7].b[0]=0x3a29; _// feed forward b0 coef_

filtArray[7].b[1]=0x8cdc; _// feed forward b1 coef_

filtArray[7].b[2]=0x3a29; _// 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_

filtArray[7].a[0]=0x8cdc; _// feedback a1 coef_

filtArray[7].a[1]=0x3452; _// 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_cascade8_fast (int16_t Xin , PARM_EQUAL_FILTER_16 * pFilter_Array );