Hello
I am using some FIR and IIR filters. I use coefficients from Dsptutor's
java applets. First of all , have you ever experienced Dpstutor's designs
on projects ?
I am using fir and iir filtering functions from Paul Embree's book. I am
building a PC\Windows application using Directshow and Winapi.
In my application , I use these filtering functions with coefficients I already
got , but unfortunately they seem not working. I mean , you can't hear any
sound after a few seconds. I am pasting my filtering functions , if it is
possible can you check them for any errors ?
/*
INPUT fInput input for filter
INPUT pCoefficients address of filter coefficients
INPUT nCoefficientNumber number of coefficients
INPUT\OUTPUT pMemory address of past values
*/
float FIRFilterEvaluate (float fInput,float* pCoefficients,int
nCoefficientNumber,float* pMemory)
{
int i ;
float *pMemoryPositioner,*pMemoryPositionerTemp,*pCoefficientPositioner ;
float fOutput ;
pMemoryPositioner = pMemory ; // We get address of pMemory to make processes on
it
pMemoryPositionerTemp = pMemoryPositioner ; // To update original history , we
need a temp pointer
pCoefficientPositioner = pCoefficients + nCoefficientNumber - 1 ; // We move
the pointer to last coefficient
// WE WILL MAKE SUMMATION OF "nCoefficientNumber" MULTIPLICATIONS
fOutput = *pMemoryPositioner++ * (*pCoefficientPositioner--); // We gave first
multiplication to summation
for(i=2 ; i
{
*pMemoryPositionerTemp++ = *pMemoryPositioner ;
fOutput += (*pMemoryPositioner++) * (*pCoefficientPositioner--) ;
}
fOutput += fInput * (*pCoefficientPositioner) ; // We gave last multiplication
to summation
*pMemoryPositionerTemp = fInput ;
return fOutput ;
}
float IIRFilterEvaluate ( float fInput,float* pCoefficients ,int n,
float * pMemory)
{
int i ;
float *pMemoryPositionerTemp1 ,*pMemoryPositionerTemp2,*pCoefficientPositioner
;
float fOutput,new_hist,history1,history2 ;
pCoefficientPositioner = pCoefficients ;
pMemoryPositionerTemp1 = pMemory ;
pMemoryPositionerTemp2 = pMemoryPositionerTemp1 + 1 ;
fOutput = fInput * (*pCoefficientPositioner++);
for(i=0 ; i
{
history1 = *pMemoryPositionerTemp1 ;
history2 = *pMemoryPositionerTemp2 ;
fOutput = fOutput - history1 * (*pCoefficientPositioner++);
new_hist = fOutput - history2 * (*pCoefficientPositioner++); // poles
fOutput = new_hist + history1 * (*pCoefficientPositioner++);
fOutput = fOutput + history2 * (*pCoefficientPositioner++ ) ; // zeros
*pMemoryPositionerTemp2++ = *pMemoryPositionerTemp1 ;
*pMemoryPositionerTemp1++ = new_hist ;
pMemoryPositionerTemp1++ ;
pMemoryPositionerTemp2++ ;
}
return fOutput ;
}
