//___________________________
void AVDMProcessAudio_Resample::InitialSRC(void)
{
int i;
frqs = 44100 * OSRM; // virtual high sampling rate
frqc = lpfcof[_quality]; // cutoff freq.
firodrv = firodr[_quality]; // FIR order = firodrv*2+1
divisor = bessel0(ALPHA);
hgain = (2.0 * ISRM * frqc) / frqs;
hfir[0] = hgain;
for (i = 1; i <= firodrv; i++)
{
regv = (double) (i * i) / (firodrv * firodrv);
wfnc = bessel0(sqrt(1.0 - regv) * ALPHA) / divisor;
regv = (2.0 * M_PI * frqc * i) / frqs;
hfir[i] = (hgain * sin(regv) * wfnc) / regv;
}
ismd = OSRM / ISRM;
ismr = OSRM % ISRM;
eptr = firodrv / ISRM;
eptrr = firodrv % ISRM;
sptr = -eptr;
sptrr = -eptr;
// ZeroMemory(smpld, sizeof(smpld));
memset(smpld, 0, sizeof(smpld));
winpos = 0;
iptr = 0;
}
double kaiser(int i, int n, double beta)
{
double a,w,a2,b1,b2,beta1;
b1 = bessel0(beta);
a = 2.0*i/(double)(n-1) - 1.0;
a2 = a*a;
beta1 = beta * sqrt(1.0 - a2);
b2 = bessel0(beta1);
w = b2/b1;
return w;
}
void
KaiserWindow::init()
{
double denominator = bessel0(m_beta);
bool even = (m_length % 2 == 0);
for (int i = 0; i < (even ? m_length/2 : (m_length+1)/2); ++i) {
double k = double(2*i) / double(m_length-1) - 1.0;
m_window.push_back(bessel0(m_beta * sqrt(1.0 - k*k)) / denominator);
}
for (int i = 0; i < (even ? m_length/2 : (m_length-1)/2); ++i) {
m_window.push_back(m_window[int(m_length/2) - i - 1]);
}
}
// static const float KAISER_ALPHA = 4.0;
static double kaiser(double alpha, double half_width, double x)
{
const double ratio = (x / half_width);
return bessel0(alpha * sqrt(1 - ratio * ratio)) / bessel0(alpha);
}
