Add drum detection for channel A in live capture

- DrumDetector.cs: 3-band onset detection (kick/snare/brass) with adaptive thresholds, per-sub-tick timing within 100ms frames - Kick: low-band onset, 150ms deep thump - Snare: broadband (mid+high) onset, 50ms mid punch - Brass: high-only onset, 10ms buzzy - Priority: kick > snare > brass when multiple hit same sub-tick - Intensity = max (100) on hit, 0 on silence — user limiter scales down - MusicAnalyzer: add BuildMelodyFrame for chB only (pitch+energy) - LiveCapture: chA now from DrumDetector, chB unchanged (melody) - Sub-tick mapping: FFT window position → 0-3 within each 100ms tick
2026-08-09 11:32:16 +00:00
parent abb5364bb4
commit 4c44d48a02
3 changed files with 182 additions and 2 deletions
@@ -0,0 +1,146 @@
+namespace Substation;
+
+public class DrumDetector
+{
+    const int HistorySize = 50;
+
+    readonly double[] _lowFluxHistory = new double[HistorySize];
+    readonly double[] _midFluxHistory = new double[HistorySize];
+    readonly double[] _highFluxHistory = new double[HistorySize];
+    int _historyIndex;
+
+    double[]? _prevLowMag;
+    double[]? _prevMidMag;
+    double[]? _prevHighMag;
+
+    readonly bool[] _subKick = new bool[4];
+    readonly bool[] _subSnare = new bool[4];
+    readonly bool[] _subBrass = new bool[4];
+
+    static readonly byte[] FreqKick = Freq.Compress4(new[] { 150, 150, 150, 150 });
+    static readonly byte[] FreqSnare = Freq.Compress4(new[] { 50, 50, 50, 50 });
+    static readonly byte[] FreqBrass = Freq.Compress4(new[] { 10, 10, 10, 10 });
+    static readonly byte[] FreqSilent = Freq.Compress4(new[] { 10, 10, 10, 10 });
+
+    public void ProcessWindow(double[] magnitude, int sampleRate, int windowSize, int subTickIndex)
+    {
+        if (subTickIndex < 0 || subTickIndex > 3) return;
+
+        double binWidth = (double)sampleRate / windowSize;
+        int lowLo = (int)(20 / binWidth), lowHi = (int)(150 / binWidth);
+        int midLo = (int)(200 / binWidth), midHi = (int)(500 / binWidth);
+        int highLo = (int)(5000 / binWidth), highHi = (int)(15000 / binWidth);
+
+        var lowMag = ExtractBand(magnitude, lowLo, lowHi);
+        var midMag = ExtractBand(magnitude, midLo, midHi);
+        var highMag = ExtractBand(magnitude, highLo, highHi);
+
+        double lowFlux = ComputeFlux(lowMag, _prevLowMag);
+        double midFlux = ComputeFlux(midMag, _prevMidMag);
+        double highFlux = ComputeFlux(highMag, _prevHighMag);
+
+        _prevLowMag = lowMag;
+        _prevMidMag = midMag;
+        _prevHighMag = highMag;
+
+        // Update history and compute adaptive thresholds
+        _lowFluxHistory[_historyIndex] = lowFlux;
+        _midFluxHistory[_historyIndex] = midFlux;
+        _highFluxHistory[_historyIndex] = highFlux;
+        _historyIndex = (_historyIndex + 1) % HistorySize;
+
+        double lowThresh = AdaptiveThreshold(_lowFluxHistory);
+        double midThresh = AdaptiveThreshold(_midFluxHistory);
+        double highThresh = AdaptiveThreshold(_highFluxHistory);
+
+        // Detect onsets
+        bool kickOnset = lowFlux > lowThresh && lowFlux > 0.001;
+        bool snareOnset = midFlux > midThresh && highFlux > highThresh && midFlux > 0.001;
+        bool brassOnset = highFlux > highThresh && !snareOnset && highFlux > 0.001;
+
+        if (kickOnset) _subKick[subTickIndex] = true;
+        if (snareOnset) _subSnare[subTickIndex] = true;
+        if (brassOnset) _subBrass[subTickIndex] = true;
+    }
+
+    public WaveFrame BuildFrame()
+    {
+        var intensity = new byte[4];
+        var freqBytes = new byte[16]; // 4 sub-ticks × 4 bytes (but we use per-sub-tick freq)
+
+        for (int i = 0; i < 4; i++)
+        {
+            byte freq;
+            if (_subKick[i])
+            {
+                intensity[i] = 100;
+                freq = Freq.Compress(150);
+            }
+            else if (_subSnare[i])
+            {
+                intensity[i] = 100;
+                freq = Freq.Compress(50);
+            }
+            else if (_subBrass[i])
+            {
+                intensity[i] = 100;
+                freq = Freq.Compress(10);
+            }
+            else
+            {
+                intensity[i] = 0;
+                freq = 10;
+            }
+
+            freqBytes[i] = freq;
+        }
+
+        // Reset for next tick
+        Array.Clear(_subKick, 0, 4);
+        Array.Clear(_subSnare, 0, 4);
+        Array.Clear(_subBrass, 0, 4);
+
+        return new WaveFrame(freqBytes, intensity);
+    }
+
+    static double[] ExtractBand(double[] magnitude, int loBin, int hiBin)
+    {
+        if (hiBin <= loBin || hiBin >= magnitude.Length)
+            return Array.Empty<double>();
+
+        var band = new double[hiBin - loBin + 1];
+        Array.Copy(magnitude, loBin, band, 0, band.Length);
+        return band;
+    }
+
+    static double ComputeFlux(double[] current, double[]? previous)
+    {
+        if (previous == null || current.Length != previous.Length) return 0;
+
+        double flux = 0;
+        for (int i = 0; i < current.Length; i++)
+        {
+            double diff = current[i] - previous[i];
+            if (diff > 0) flux += diff;
+        }
+        return flux;
+    }
+
+    static double AdaptiveThreshold(double[] history)
+    {
+        double sum = 0, sumSq = 0;
+        int count = 0;
+        foreach (var v in history)
+        {
+            if (v <= 0) continue;
+            sum += v;
+            sumSq += v * v;
+            count++;
+        }
+        if (count == 0) return double.MaxValue;
+        double mean = sum / count;
+        double variance = sumSq / count - mean * mean;
+        double stddev = variance > 0 ? Math.Sqrt(variance) : 0;
+        return mean + 2 * stddev;
+    }
+}