/// <summary>
/// Used for debugging purposes.
/// </summary>
public static void Print(TextWriter writer, TriangleFilter f)
{
for (int i = 0; i < f.leftEdge; ++i)
{
if (i != 0)
{
writer.Write(", ");
}
writer.Write("0");
}
for (int i = 0; i < f.size; ++i)
{
writer.Write(", " + f.FilterData[i].ToString("0.000", CultureInfo.InvariantCulture));
}
}
/// <summary>
/// Creates a new MelFilterBank.
/// </summary>
/// <param name="minFreq">The minimum frequency in hz to be considered, i.e.
/// the left edge of the first TriangleFilter.</param>
/// <param name="maxFreq">The maximum frequency in hz to be considered, i.e.
/// the right edge of the last TriangleFilter.</param>
/// <param name="numMelBands">The number of Mel bands to be calculated, i.e.
/// the number of TriangleFilters to be applied.</param>
/// <param name="numBins">The number of bins that are present in the fft_buffer
/// that will be passed to the MelFilterBank.Apply method. This is also
/// required to properly configure the TriangleFilter instances which
/// operate on array indices only. (half the window size)</param>
/// <param name="sampleRate">The original sample rate the FFT buffer which will
/// be passed to MelFilterBank.Apply is based on.</param>
/// <param name="doNormalizeFilterArea">If set to "true", the area of the
/// created TriangleFilter will be normalized, e.g. the height of the
/// filter's triangle shape will be configured in a way, that the area
/// of the triangle shape equals one.</param>
public MelFilterBank(double minFreq, double maxFreq, int numMelBands, int numBins, int sampleRate, bool doNormalizeFilterArea)
{
this.minFreq = minFreq;
this.maxFreq = maxFreq;
this.numMelBands = numMelBands;
this.numBins = numBins;
this.sampleRate = sampleRate;
this.doNormalizeFilterArea = doNormalizeFilterArea;
// Let's do some argument checking
if ((minFreq >= maxFreq) || (maxFreq == 0))
{
throw new ArgumentException(String.Format("Invalid min/max frequencies for MelFilterBank: min = '{0}' max = '{1}'", minFreq, maxFreq));
}
if (numMelBands == 0)
{
throw new ArgumentException(String.Format("Invalid number of mel bands for MelFilterBank: n = {0}", numMelBands));
}
if (sampleRate == 0)
{
throw new ArgumentException(String.Format("Invalid sample rate for MelFilterBank: s = {0}", sampleRate));
}
if (numBins == 0)
{
throw new ArgumentException(String.Format("Invalid number of bins for MelFilterBank: s = '{0}'", numBins));
}
// 2 * numBins should be the same as window length
double deltaFreq = (double)sampleRate / (2 * numBins);
double melMin = MelUtils.LinToMelFreq(minFreq);
double melMax = MelUtils.LinToMelFreq(maxFreq);
// We divide by #band + 1 as min / max should present the beginning / end
// of beginng up / ending low slope, i.e. it's not the centers of each
// band that represent min/max frequency in mel bands.
double deltaFreqMel = (melMax - melMin) / (numMelBands + 1);
// Fill up equidistant spacing in mel-space
double melLeft = melMin;
for (int i = 0; i < numMelBands; i++)
{
double melCenter = melLeft + deltaFreqMel;
double melRight = melCenter + deltaFreqMel;
double leftHz = MelUtils.MelToLinFreq(melLeft);
double rightHz = MelUtils.MelToLinFreq(melRight);
// align to closest num_bins (round)
int leftBin = (int)((leftHz / deltaFreq) + 0.5);
int rightBin = (int)((rightHz / deltaFreq) + 0.5);
// calculate normalized height
double height = 1.0;
if (doNormalizeFilterArea)
{
height = 2.0 / (rightBin - leftBin);
}
// Create the actual filter
var filter = new TriangleFilter(leftBin, rightBin, height);
filters.Add(filter);
// next left edge is current center
melLeft = melCenter;
}
}
