/// <summary>
/// This method returns spectral peak tracks enclosed in acoustic events.
/// It averages dB log values incorrectly but it is faster than doing many log conversions.
/// </summary>
public static (List <AcousticEvent> Events, double[] CombinedIntensity) GetSpectralPeakTracks(
SpectrogramStandard sonogram,
int minHz,
int maxHz,
int nyquist,
double decibelThreshold,
double minDuration,
double maxDuration,
bool combinePossibleHarmonics,
TimeSpan segmentStartOffset)
{
var sonogramData = sonogram.Data;
int frameCount = sonogramData.GetLength(0);
int binCount = sonogramData.GetLength(1);
double binWidth = nyquist / (double)binCount;
int minBin = (int)Math.Round(minHz / binWidth);
int maxBin = (int)Math.Round(maxHz / binWidth);
int bandwidthBinCount = maxBin - minBin + 1;
var frameDuration = sonogram.FrameDuration;
var frameStep = sonogram.FrameStep;
var frameOverStep = frameDuration - frameStep;
// list of accumulated acoustic events
var events = new List <AcousticEvent>();
//Find all spectral peaks and place in peaks matrix
var peaks = new double[frameCount, bandwidthBinCount];
for (int row = 0; row < frameCount; row++)
{
for (int col = minBin - 1; col < maxBin - 1; col++)
{
if (sonogramData[row, col] < decibelThreshold)
{
continue;
}
// if given matrix element is greater than in freq bin either side
bool isPeak = (sonogramData[row, col] > sonogramData[row, col - 1]) && (sonogramData[row, col] > sonogramData[row, col + 1]);
if (isPeak)
{
peaks[row, col] = sonogramData[row, col];
}
}
}
// Look for track starts and initialise them as events.
// Cannot include edge rows & columns because of edge effects.
// Each row is a time frame which is a spectrum. Each column is a frequency bin
var combinedIntensityArray = new double[frameCount];
for (int row = 0; row < frameCount; row++)
{
for (int col = 3; col < bandwidthBinCount - 3; col++)
{
// Visit each spectral peak in order. Each may be start of possible track
if (peaks[row, col] < decibelThreshold)
{
continue;
}
//have the beginning of a potential track
var track = GetTrack(peaks, row, col, decibelThreshold);
int trackStartFrame = track.GetStartFrame();
int trackEndFrame = track.GetEndFrame();
double trackDuration = ((trackEndFrame - trackStartFrame) * frameStep) + frameOverStep;
// calculate max and min bin IDs in the original spectrogram
int trackBottomBin = track.GetBottomFreqBin();
int trackTopBin = track.GetTopFreqBin();
//If track has length within duration bounds, then create an event
if (trackDuration >= minDuration && trackDuration <= maxDuration)
{
var oblong = new Oblong(track.GetStartFrame(), trackBottomBin, track.GetEndFrame(), trackTopBin);
var ae = new AcousticEvent(segmentStartOffset, oblong, nyquist, binCount, frameDuration, frameStep, frameCount)
{
// get the track as matrix
TheTrack = track,
};
events.Add(ae);
// fill the intensity array
var amplitudeTrack = track.GetAmplitudeOverTimeFrames();
for (int i = 0; i < amplitudeTrack.Length; i++)
{
combinedIntensityArray[row + i] += amplitudeTrack[i];
}
}
}
}
// Combine coincident events that are stacked one above other.
// This will help in some cases to combine related events.
var startDifference = TimeSpan.FromSeconds(0.2);
var hertzGap = 200;
if (combinePossibleHarmonics)
{
events = AcousticEvent.CombinePotentialStackedTracks(events, startDifference, hertzGap);
}
return(events, combinedIntensityArray);
}
