//////////////////////////////////////////////////////////////////////
// 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
}
////////////////////////////////////////////////////////////////////
// Create a FIR high Pass filter with scaled amplitude 'Scale'
// NumTaps if non-zero, forces filter design to be this number of taps
// Astop = Stopband Atenuation in dB (ie 40dB is 40dB stopband attenuation)
// Fpass = Highpass passband frequency in Hz
// Fstop = Highpass stopband frequency in Hz
// Fsamprate = Sample Rate in Hz
//
// Apass -------------
// /
// /
// /
// /
// Astop ---------
// Fstop Fpass
////////////////////////////////////////////////////////////////////
int CFir::InitHPFilter(int NumTaps, TYPEREAL Scale, TYPEREAL Astop, TYPEREAL Fpass, TYPEREAL Fstop, TYPEREAL Fsamprate)
{
int n;
TYPEREAL Beta;
//m_Mutex.lock();
m_SampleRate = Fsamprate;
//create normalized frequency parameters
TYPEREAL normFpass = Fpass/Fsamprate;
TYPEREAL normFstop = Fstop/Fsamprate;
TYPEREAL normFcut = (normFstop + normFpass)/2.0; //high pass filter 6dB cutoff
//calculate Kaiser-Bessel window shape factor, Beta, from stopband attenuation
if(Astop < 20.96)
Beta = 0;
else if(Astop >= 50.0)
Beta = .1102 * (Astop - 8.71);
else
Beta = .5842 * MPOW( (Astop-20.96), 0.4) + .07886 * (Astop - 20.96);
//Now Estimate number of filter taps required based on filter specs
m_NumTaps = (Astop - 8.0) / (2.285*K_2PI*(normFpass - normFstop ) ) + 1;
//clamp range of filter taps
if(m_NumTaps>(MAX_NUMCOEF-1) )
m_NumTaps = MAX_NUMCOEF-1;
if(m_NumTaps < 3)
m_NumTaps = 3;
m_NumTaps |= 1; //force to next odd number
if(NumTaps) //if need to force to to a number of taps
m_NumTaps = NumTaps;
TYPEREAL izb = Izero(Beta); //precalculate denominator since is same for all points
TYPEREAL fCenter = .5*(TYPEREAL)(m_NumTaps-1);
for( n=0; n < m_NumTaps; n++)
{
TYPEREAL x = (TYPEREAL)n - (TYPEREAL)(m_NumTaps-1)/2.0;
TYPEREAL c;
// create ideal Sinc() HP filter with normFcut
if( (TYPEREAL)n == fCenter ) //deal with odd size filter singularity where sin(0)/0==1
c = 1.0 - 2.0 * normFcut;
else
c = (TYPEREAL) (MSIN(K_PI*x)/(K_PI*x) - MSIN(K_2PI*x*normFcut)/(K_PI*x) );
//calculate Kaiser window and multiply to get coefficient
x = ((TYPEREAL)n - ((TYPEREAL)m_NumTaps-1.0)/2.0 ) / (((TYPEREAL)m_NumTaps-1.0)/2.0);
m_Coef[n] = Scale * c * Izero( Beta * MSQRT(1 - (x*x) ) ) / izb;
}
//make a 2x length array for FIR flat calculation efficiency
for (n = 0; n < m_NumTaps; n++)
m_Coef[n+m_NumTaps] = m_Coef[n];
//copy into complex coef buffers
for (n = 0; n < m_NumTaps*2; n++)
{
m_ICoef[n] = m_Coef[n];
m_QCoef[n] = m_Coef[n];
}
//Initialize the FIR buffers and state
for(int i=0; i<m_NumTaps; i++)
{
m_rZBuf[i] = 0.0;
m_cZBuf[i].re = 0.0;
m_cZBuf[i].im = 0.0;
}
m_State = 0;
//m_Mutex.unlock();
#if 0 //debug hack to write m_Coef to a file for analysis
QDir::setCurrent("d:/");
QFile File;
File.setFileName("hpcoef.txt");
if(File.open(QIODevice::WriteOnly))
{
qDebug()<<"file Opened OK";
char Buf[256];
for(n=0; n<m_NumTaps; n++)
{
sprintf( Buf, "%g\r\n", m_Coef[n]);
File.write(Buf);
}
}
else
qDebug()<<"file Failed to Open";
qDebug()<<"HP taps="<<m_NumTaps;
#endif
return m_NumTaps;
}