/// <summary>
/// A METHOD TO DETECT HARMONICS IN THE sub-band of a spectrogram.
/// This method assume the matrix is derived from a spectrogram rotated so that the matrix rows are spectral columns of the spectrogram.
/// Developed for GenericRecognizer of harmonics.
/// WARNING: As of March 2020, this method averages the values in five adjacent frames. This is to reduce noise.
/// But it requires that the frequency of any potential formants is not changing rapidly.
/// THis may not be suitable for detecting human speech. However can reduce the frame step.
/// </summary>
/// <param name="m">spectrogram data matrix.</param>
/// <param name="dBThreshold">Minimum sound level.</param>
/// <returns>three arrays: dBArray, intensity, maxIndexArray.</returns>
public static Tuple <double[], double[], int[]> DetectHarmonicsInSpectrogramData(double[,] m, double dBThreshold)
{
int rowCount = m.GetLength(0);
int colCount = m.GetLength(1);
var binCount = m.GetLength(1);
//set up the cosine coefficients
double[,] cosines = MFCCStuff.Cosines(binCount, binCount);
// set up arrays to store decibels, formant intensity and max index.
var dBArray = new double[rowCount];
var intensity = new double[rowCount];
var maxIndexArray = new int[rowCount];
// for all time frames
for (int t = 2; t < rowCount - 2; t++)
{
// get average of five adjacent frames
var frame1 = MatrixTools.GetRow(m, t - 2);
var frame2 = MatrixTools.GetRow(m, t - 1);
var frame3 = MatrixTools.GetRow(m, t);
var frame4 = MatrixTools.GetRow(m, t + 1);
var frame5 = MatrixTools.GetRow(m, t + 2);
var frame = new double[colCount];
for (int i = 0; i < colCount; i++)
{
frame[i] = (frame1[i] + frame2[i] + frame3[i] + frame4[i] + frame5[i]) / 5;
}
double maxValue = frame.Max();
dBArray[t] = maxValue;
if (maxValue < dBThreshold)
{
continue;
}
double[] xr = AutoAndCrossCorrelation.AutoCrossCorr(frame);
// xr has twice length of frame and is symmetrical.
// Require only first half.
double[] normXr = new double[colCount];
for (int i = 0; i < colCount; i++)
{
// Would normally normalise the xcorr values for overlap count.
// But for harmonics, this introduces too much noise - need to give less weight to the less overlapped values.
//normXr[i] = xr[i] / (colCount - i);
normXr[i] = xr[i];
}
// now do DCT across the auto cross xr
int lowerDctBound = 2;
var dctCoefficients = Oscillations2012.DoDct(normXr, cosines, lowerDctBound);
int indexOfMaxValue = DataTools.GetMaxIndex(dctCoefficients);
intensity[t] = dctCoefficients[indexOfMaxValue];
maxIndexArray[t] = indexOfMaxValue;
}
return(Tuple.Create(dBArray, intensity, maxIndexArray));
}
/// <summary>
/// A METHOD TO DETECT HARMONICS IN THE sub-band of a sonogram.
/// This method assume the matrix is derived from a spectrogram rotated so that the matrix rows are spectral columns of sonogram.
/// Developed for GenericRecognizer of harmonics.
/// </summary>
/// <param name="m">data matrix.</param>
/// <param name="dBThreshold">Minimum sound level.</param>
/// <returns>two arrays.</returns>
public static Tuple <double[], double[], int[]> DetectHarmonicsInSonogramMatrix(double[,] m, double dBThreshold)
{
int rowCount = m.GetLength(0);
int colCount = m.GetLength(1);
double[] dBArray = new double[rowCount];
var intensity = new double[rowCount]; //an array of formant intensity
var maxIndexArray = new int[rowCount]; //an array of max value index values
var binCount = m.GetLength(1);
double[,] cosines = MFCCStuff.Cosines(binCount, binCount); //set up the cosine coefficients
// for all time frames
for (int t = 0; t < rowCount; t++)
{
var frame = MatrixTools.GetRow(m, t);
double maxValue = frame.Max();
dBArray[t] = maxValue;
if (maxValue < dBThreshold)
{
continue;
}
double[] xr = AutoAndCrossCorrelation.AutoCrossCorr(frame);
// xr has twice length of frame and is symmetrical.
// Require only first half. Also need to normalise the values for overlap count.
double[] normXr = new double[colCount];
for (int i = 0; i < colCount; i++)
{
normXr[i] = xr[i] / (colCount - i);
}
// now do DCT across the auto cross xr
int lowerDctBound = 2;
var dctCoefficients = Oscillations2012.DoDct(normXr, cosines, lowerDctBound);
int indexOfMaxValue = DataTools.GetMaxIndex(dctCoefficients);
intensity[t] = dctCoefficients[indexOfMaxValue];
maxIndexArray[t] = indexOfMaxValue;
} // frames = rows of matrix
return(Tuple.Create(dBArray, intensity, maxIndexArray));
}
