/// <summary>
/// Calculates the modal noise value for each freq bin.
/// Does so using a series of overlapped matrices.
/// TODO!!!! COULD SIMPLY THIS METHOD. JUST CALCULATE MODE FOR EACH FREQ BIN WITHOUT OVERLAP ....
/// .... AND THEN APPLY MORE SEVERE SMOOTHING TO THE MODAL NOISE PROFILE IN PREVIOUS METHOD.
///
/// COMPARE THIS METHOD WITH SNR.SubtractModalNoise().
/// </summary>
/// <param name="matrix">Audio sample matrix.</param>
/// <returns>Modal noise values.</returns>
private static double[] CalculateModalNoise(double[,] matrix)
{
//set parameters for noise histograms based on overlapping bands.
//*******************************************************************************************************************
int bandWidth = 3; // should be an odd number
int binCount = 64; // number of pixel intensity bins
double upperLimitForMode = 0.666; // sets upper limit to modal noise bin. Higher values = more severe noise removal.
int binLimit = (int)(binCount * upperLimitForMode);
//*******************************************************************************************************************
DoubleSquareArrayExtensions.MinMax(matrix, out var minIntensity, out var maxIntensity);
double binWidth = (maxIntensity - minIntensity) / binCount; // width of an intensity bin
// LoggedConsole.WriteLine("minIntensity=" + minIntensity + " maxIntensity=" + maxIntensity + " binWidth=" + binWidth);
int rowCount = matrix.GetLength(0);
int colCount = matrix.GetLength(1);
if (bandWidth > colCount)
{
bandWidth = colCount - 1;
}
int halfWidth = bandWidth / 2;
// init matrix from which histogram derived
double[,] submatrix = Submatrix(matrix, 0, 0, rowCount - 1, bandWidth);
double[] modalNoise = new double[colCount];
// for all cols i.e. freq bins
for (int col = 0; col < colCount; col++)
{
// construct new submatrix to calculate modal noise
int start = col - halfWidth; //extend range of submatrix below col for smoother changes
if (start < 0)
{
start = 0;
}
int stop = col + halfWidth;
if (stop >= colCount)
{
stop = colCount - 1;
}
submatrix = Submatrix(matrix, 0, start, rowCount - 1, stop);
int[] histo = Histo(submatrix, binCount, minIntensity, maxIntensity, binWidth);
//DataTools.writeBarGraph(histo);
double[] smoothHisto = FilterMovingAverage(histo, 7);
GetMaxIndex(smoothHisto, out var maxindex); //this is mode of histogram
if (maxindex > binLimit)
{
maxindex = binLimit;
}
modalNoise[col] = minIntensity + (maxindex * binWidth);
//LoggedConsole.WriteLine(" modal index=" + maxindex + " modalIntensity=" + modalIntensity.ToString("F3"));
}
return(modalNoise);
}
