//////////////////////////////////////////////////////////////////////
// Call to setup filter parameters
// SampleRate in Hz
// FLowcut is low cutoff frequency of filter in Hz
// FHicut is high cutoff frequency of filter in Hz
// Offset is the CW tone offset frequency
// cutoff frequencies range from -SampleRate/2 to +SampleRate/2
// HiCut must be greater than LowCut
// example to make 2700Hz USB filter:
// SetupParameters( 100, 2800, 0, 48000);
//////////////////////////////////////////////////////////////////////
void CFastFIR::SetupParameters( TYPEREAL FLoCut, TYPEREAL FHiCut,
TYPEREAL Offset, TYPEREAL SampleRate)
{
int i;
if( (FLoCut==m_FLoCut) && (FHiCut==m_FHiCut) &&
(Offset==m_Offset) && (SampleRate==m_SampleRate) )
{
return; //return if no changes
}
m_FLoCut = FLoCut;
m_FHiCut = FHiCut;
m_Offset = Offset;
m_SampleRate = SampleRate;
FLoCut += Offset;
FHiCut += Offset;
//sanity check on filter parameters
if( (FLoCut >= FHiCut) ||
(FLoCut >= SampleRate/2.0) ||
(FLoCut <= -SampleRate/2.0) ||
(FHiCut >= SampleRate/2.0) ||
(FHiCut <= -SampleRate/2.0) )
{
fprintf(stderr, "Filter Parameter error:\n");
return;
}
//calculate some normalized filter parameters
TYPEREAL nFL = FLoCut/SampleRate;
TYPEREAL nFH = FHiCut/SampleRate;
TYPEREAL nFc = (nFH-nFL)/2.0; //prototype LP filter cutoff
TYPEREAL nFs = K_2PI*(nFH+nFL)/2.0; //2 PI times required frequency shift (FHiCut+FLoCut)/2
TYPEREAL fCenter = 0.5*(TYPEREAL)(CONV_FIR_SIZE-1); //floating point center index of FIR filter
for(i=0; i<CONV_FFT_SIZE; i++) //zero pad entire coefficient buffer to FFT size
{
m_pFilterCoef[i].re = 0.0;
m_pFilterCoef[i].im = 0.0;
}
//create LP FIR windowed sinc, sin(x)/x complex LP filter coefficients
for(i=0; i<CONV_FIR_SIZE; i++)
{
TYPEREAL x = (TYPEREAL)i - fCenter;
TYPEREAL z;
if( (TYPEREAL)i == fCenter ) //deal with odd size filter singularity where sin(0)/0==1
z = 2.0 * nFc;
else
z = (TYPEREAL)MSIN(K_2PI*x*nFc)/(K_PI*x) * m_pWindowTbl[i];
//shift lowpass filter coefficients in frequency by (hicut+lowcut)/2 to form bandpass filter anywhere in range
// (also scales by 1/FFTsize since inverse FFT routine scales by FFTsize)
m_pFilterCoef[i].re = z * MCOS(nFs * x)/(TYPEREAL)CONV_FFT_SIZE;
m_pFilterCoef[i].im = z * MSIN(nFs * x)/(TYPEREAL)CONV_FFT_SIZE;
}
//convert FIR coefficients to frequency domain by taking forward FFT
m_Fft.FwdFFT(m_pFilterCoef);
}
///////////////////////////////////////////////////////////////////////////
// function to convert LP filter coefficients into complex hilbert bandpass
// filter coefficients.
// Hbpreal(n)= 2*Hlp(n)*MCOS( 2PI*FreqOffset*(n-(N-1)/2)/samplerate );
// Hbpimaj(n)= 2*Hlp(n)*MSIN( 2PI*FreqOffset*(n-(N-1)/2)/samplerate );
void CFir::GenerateHBFilter( TYPEREAL FreqOffset)
{
int n;
for(n=0; n<m_NumTaps; n++)
{
// apply complex frequency shift transform to low pass filter coefficients
m_ICoef[n] = 2.0 * m_Coef[n] * MCOS( (K_2PI*FreqOffset/m_SampleRate)*((TYPEREAL)n - ( (TYPEREAL)(m_NumTaps-1)/2.0 ) ) );
m_QCoef[n] = 2.0 * m_Coef[n] * MSIN( (K_2PI*FreqOffset/m_SampleRate)*((TYPEREAL)n - ( (TYPEREAL)(m_NumTaps-1)/2.0 ) ) );
}
//make a 2x length array for FIR flat calculation efficiency
for (n = 0; n < m_NumTaps; n++)
{
m_ICoef[n+m_NumTaps] = m_ICoef[n];
m_QCoef[n+m_NumTaps] = m_QCoef[n];
}
#if 0 //debug hack to write m_Coef's to a file for analysis
QDir::setCurrent("d:/");
QFile File;
File.setFileName("hbpcoef.txt");
if(File.open(QIODevice::WriteOnly))
{
qDebug()<<"file Opened OK";
char Buf[256];
for( n=0; n<m_NumTaps; n++)
{
sprintf( Buf, "%19.12g %19.12g\r\n", m_ICoef[n], m_QCoef[n]);
File.write(Buf);
}
}
else
qDebug()<<"file Failed to Open";
qDebug()<<"HBP taps="<<m_NumTaps << m_SampleRate;
#endif
}
CFastFIR::CFastFIR()
{
int i;
m_pWindowTbl = NULL;
m_pFFTBuf = NULL;
m_pFFTOverlapBuf = NULL;
m_pFilterCoef = NULL;
//allocate internal buffer space on Heap
m_pWindowTbl = new TYPEREAL[CONV_FIR_SIZE];
m_pFilterCoef = new TYPECPX[CONV_FFT_SIZE];
m_pFFTBuf = new TYPECPX[CONV_FFT_SIZE];
m_pFFTOverlapBuf = new TYPECPX[CONV_FIR_SIZE];
if(!m_pWindowTbl || !m_pFilterCoef || !m_pFFTBuf || !m_pFFTOverlapBuf)
{
//major poblems if memory fails here
return;
}
m_InBufInPos = (CONV_FIR_SIZE - 1);
for( i=0; i<CONV_FFT_SIZE; i++)
{
m_pFFTBuf[i].re = 0.0;
m_pFFTBuf[i].im = 0.0;
}
#if 1
//create Blackman-Nuttall window function for windowed sinc low pass filter design
for( i=0; i<CONV_FIR_SIZE; i++)
{
m_pWindowTbl[i] = (0.3635819
- 0.4891775*MCOS( (K_2PI*i)/(CONV_FIR_SIZE-1) )
+ 0.1365995*MCOS( (2.0*K_2PI*i)/(CONV_FIR_SIZE-1) )
- 0.0106411*MCOS( (3.0*K_2PI*i)/(CONV_FIR_SIZE-1) ) );
m_pFFTOverlapBuf[i].re = 0.0;
m_pFFTOverlapBuf[i].im = 0.0;
}
#endif
#if 0
//create Blackman-Harris window function for windowed sinc low pass filter design
for( i=0; i<CONV_FIR_SIZE; i++)
{
m_pWindowTbl[i] = (0.35875
- 0.48829*MCOS( (K_2PI*i)/(CONV_FIR_SIZE-1) )
+ 0.14128*MCOS( (2.0*K_2PI*i)/(CONV_FIR_SIZE-1) )
- 0.01168*MCOS( (3.0*K_2PI*i)/(CONV_FIR_SIZE-1) ) );
m_pFFTOverlapBuf[i].re = 0.0;
m_pFFTOverlapBuf[i].im = 0.0;
}
#endif
#if 0
//create Nuttall window function for windowed sinc low pass filter design
for( i=0; i<CONV_FIR_SIZE; i++)
{
m_pWindowTbl[i] = (0.355768
- 0.487396*MCOS( (K_2PI*i)/(CONV_FIR_SIZE-1) )
+ 0.144232*MCOS( (2.0*K_2PI*i)/(CONV_FIR_SIZE-1) )
- 0.012604*MCOS( (3.0*K_2PI*i)/(CONV_FIR_SIZE-1) ) );
m_pFFTOverlapBuf[i].re = 0.0;
m_pFFTOverlapBuf[i].im = 0.0;
}
#endif
m_Fft.SetFFTParams(CONV_FFT_SIZE, false, 0.0, 1.0);
m_FLoCut = -1.0;
m_FHiCut = 1.0;
m_Offset = 1.0;
m_SampleRate = 1.0;
}
