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namespace Godosa.Core.Audio;
/// <summary>Signal measurements for audio tests and reports: zero crossings, RMS, spectral centroid.</summary>
public static class SignalStats
{
public static int ZeroCrossings(float[] x, int from = 0, int to = -1)
{
if (to < 0) to = x.Length;
int n = 0;
for (int i = from + 1; i < to; i++) if ((x[i - 1] < 0) != (x[i] < 0)) n++;
return n;
}
public static float Rms(float[] x, int from = 0)
{
double sum = 0;
for (int i = from; i < x.Length; i++) sum += x[i] * x[i];
return (float)Math.Sqrt(sum / (x.Length - from));
}
/// <summary>Power-weighted mean frequency (where the energy is) of the loudest 2048-sample
/// window, naive DFT. Magnitude weighting over-counts faint broadband tails.</summary>
public static float Centroid(short[] pcm, int rate = Pcm.SampleRate)
{
const int n = 2048;
int best = 0;
double bestEnergy = -1;
for (int start = 0; start + n <= Math.Max(pcm.Length, n); start += n / 2)
{
double e = 0;
for (int i = start; i < Math.Min(pcm.Length, start + n); i++) e += (double)pcm[i] * pcm[i];
if (e > bestEnergy) (bestEnergy, best) = (e, start);
}
double weighted = 0, total = 0;
for (int k = 1; k < n / 2; k++)
{
double re = 0, im = 0;
for (int i = 0; i < n; i++)
{
double v = best + i < pcm.Length ? pcm[best + i] : 0;
double a = 2 * Math.PI * k * i / n;
re += v * Math.Cos(a);
im -= v * Math.Sin(a);
}
double power = re * re + im * im;
weighted += power * k * rate / (double)n;
total += power;
}
return (float)(weighted / total);
}
}
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