/**
* Creates all the filters in the bank.
*
* @param sampleFrequency sample frequency in Hz
* @param melFilterWidth filter width in Mel frequency scale
* @param N spectrum size of each filter
*/
public MelFiltersBank(double sampleFrequency, ushort melFilterWidth, int N)
{
sampleFreq = sampleFrequency;
N_ = N;
for (int i = 0; i < Dtw.MELFILTERS; ++i)
{
//filters.push_back(new MelFilter(sampleFrequency));
MelFilter filter = new MelFilter(sampleFrequency);
filter.CreateFilter(i, melFilterWidth, N);
filters.Add(filter);
}
}
/**
* Creates all the filters in the bank.
*
* @param sampleFrequency sample frequency in Hz
* @param melFilterWidth filter width in Mel frequency scale
* @param N spectrum size of each filter
*/
public MelFiltersBank(double sampleFrequency, ushort melFilterWidth, int N)
{
sampleFreq = sampleFrequency;
N_ = N;
for (int i = 0; i < Dtw.MELFILTERS; ++i)
{
//filters.push_back(new MelFilter(sampleFrequency));
MelFilter filter = new MelFilter(sampleFrequency);
filter.CreateFilter(i, melFilterWidth, N);
filters.Add(filter);
}
}
public MelFiltersBank(double sampleFrequency, int N, bool isHfcc)
{
sampleFreq = sampleFrequency;
N_ = N;
// and here the magic happens ;)
double f_low_global = 0.0;
double f_high_global = sampleFrequency / 2.0;
const double a = 6.23e-6;
const double b = 93.39e-3;
const double c = 28.52;
double a1 = 0.0;
double b1 = 0.0;
double c1 = 0.0;
double b2 = 0.0;
double c2 = 0.0;
a1 = 0.5 / (700.0 + f_low_global);
b1 = 700 / (700.0 + f_low_global);
c1 = (-f_low_global / 2.0) * (1.0 + 700 / (700.0 + f_low_global));
b2 = (b - b1) / (a - a1);
c2 = (c - c1) / (a - a1);
double fc_0 = 0.5 * (-b2 + Math.Sqrt(b2 * b2 - 4 * c2));
a1 = -0.5 / (700.0 + f_high_global);
b1 = -700 / (700.0 + f_high_global);
c1 = (f_high_global / 2.0) * (1.0 + 700 / (700.0 + f_high_global));
b2 = (b - b1) / (a - a1);
c2 = (c - c1) / (a - a1);
double fc_last = 0.5 * (-b2 + Math.Sqrt(b2 * b2 - 4 * c2));
double fc_0_mel = MelFilter.LinearToMel(fc_0);
double fc_last_mel = MelFilter.LinearToMel(fc_last);
double delta_f_mel = (fc_last_mel - fc_0_mel) / (double)(Dtw.MELFILTERS - 1);
double fc_mel = 0.0;
double fc = 0.0;
double ERB = 0.0;
double f_low = 0.0;
double f_high;
//filters.reserve(Dtw.MELFILTERS);
for (int i = 0; i < Dtw.MELFILTERS; i++)
{
if (0 == i)
{
fc_mel = fc_0_mel;
}
else if ((Dtw.MELFILTERS - 1) == i)
{
fc_mel = fc_last_mel;
}
else
{
fc_mel = fc_0_mel + i * delta_f_mel;
}
// convert to linear scale, calculate ERB and filter boundaries
fc = MelFilter.MelToLinear(fc_mel);
ERB = a * fc * fc + b * fc + c;
f_low = -(700.0 + ERB) + Math.Sqrt((700.0 + ERB) * (700.0 + ERB) + fc * (fc + 1400));
f_high = f_low + 2 * ERB;
//filters.push_back(new MelFilter(sampleFrequency));
filters[i].GenerateFilterSpectrum(f_low, fc, f_high, N);
}
}