/// <summary>
/// Pitch estimation by autocorrelation method
/// </summary>
/// <param name="signal"></param>
/// <param name="samplingRate"></param>
/// <param name="startPos"></param>
/// <param name="endPos"></param>
/// <param name="low"></param>
/// <param name="high"></param>
/// <returns></returns>
public static float FromAutoCorrelation(float[] signal,
int samplingRate,
int startPos = 0,
int endPos = -1,
float low = 80,
float high = 400)
{
if (endPos == -1)
{
endPos = signal.Length;
}
var pitch1 = (int)(1.0 * samplingRate / high); // 2,5 ms = 400Hz
var pitch2 = (int)(1.0 * samplingRate / low); // 12,5 ms = 80Hz
var block = new DiscreteSignal(samplingRate, signal)[startPos, endPos].Samples;
var fftSize = MathUtils.NextPowerOfTwo(2 * block.Length - 1);
var cc = new float[fftSize];
new Convolver(fftSize).CrossCorrelate(block, block.FastCopy(), cc);
var start = pitch1 + block.Length - 1;
var end = Math.Min(start + pitch2, cc.Length);
var max = start < cc.Length ? cc[start] : 0;
var peakIndex = start;
for (var k = start; k < end; k++)
{
if (cc[k] > max)
{
max = cc[k];
peakIndex = k - block.Length + 1;
}
}
return(max > 1.0f ? (float)samplingRate / peakIndex : 0);
}