diff --git a/LiveCapture.cs b/LiveCapture.cs
index d1b7a79..ab48f61 100644
--- a/LiveCapture.cs
+++ b/LiveCapture.cs
@@ -1,6 +1,7 @@
 using FftSharp;
 using NAudio.CoreAudioApi;
 using NAudio.Wave;
+using System.IO;
 
 namespace Substation;
 
@@ -21,6 +22,23 @@ public class LiveCapture : IDisposable
     int _fftIndexInTick;
     readonly DrumDetector _drums = new();
 
+    int _dataAvailableCount;
+    int _totalSamplesReceived;
+    int _fftCount;
+    int _tickCount;
+
+    static readonly string LogPath = Path.Combine(AppContext.BaseDirectory, "live.log");
+    static readonly object LogLock = new();
+
+    static void Log(string msg)
+    {
+        var line = $"{DateTime.Now:HH:mm:ss.fff} {msg}";
+        lock (LogLock)
+        {
+            try { File.AppendAllText(LogPath, line + Environment.NewLine); } catch { }
+        }
+    }
+
     public event Action? Stopped;
 
     public LiveCapture(State state, MMDevice device)
@@ -36,6 +54,12 @@ public class LiveCapture : IDisposable
         _sampleRate = _capture.WaveFormat.SampleRate;
         _fftsPerTick = Math.Max(1, (int)Math.Round(MusicAnalyzer.TickDuration * _sampleRate / MusicAnalyzer.HopSize));
 
+        try { File.WriteAllText(LogPath, ""); } catch { }
+
+        Log($"[live] device: {_device.FriendlyName}");
+        Log($"[live] format: {_capture.WaveFormat} ({_capture.WaveFormat.BitsPerSample}bit, {_capture.WaveFormat.Channels}ch, {_sampleRate}Hz)");
+        Log($"[live] fftsPerTick: {_fftsPerTick}");
+
         _capture.DataAvailable += OnDataAvailable;
         _capture.RecordingStopped += OnRecordingStopped;
 
@@ -43,7 +67,8 @@ public class LiveCapture : IDisposable
         _processThread.Start();
 
         _capture.StartRecording();
-        Console.WriteLine($"[live] capture started: {_device.FriendlyName} ({_sampleRate}Hz, {_capture.WaveFormat.Channels}ch)");
+        Log($"[live] capture started");
+        Log($"[live] log file: {LogPath}");
     }
 
     public void Stop()
@@ -59,6 +84,12 @@ public class LiveCapture : IDisposable
         int frameSize = channels * bytesPerSample;
         int sampleCount = e.BytesRecorded / frameSize;
 
+        _dataAvailableCount++;
+        _totalSamplesReceived += sampleCount;
+
+        if (_dataAvailableCount % 100 == 1)
+            Log($"[live] dataAvailable #{_dataAvailableCount}: {e.BytesRecorded} bytes, {sampleCount} samples, total={_totalSamplesReceived}, buffer={_sampleBuffer.Count}");
+
         lock (_bufferLock)
         {
             for (int i = 0; i < sampleCount; i++)
@@ -81,7 +112,9 @@ public class LiveCapture : IDisposable
     {
         _running = false;
         Stopped?.Invoke();
-        Console.WriteLine("[live] capture stopped");
+        Log($"[live] capture stopped. dataAvailable={_dataAvailableCount}, totalSamples={_totalSamplesReceived}, ffts={_fftCount}, ticks={_tickCount}");
+        if (e?.Exception != null)
+            Log($"[live] ERROR stop exception: {e.Exception.Message}");
     }
 
     void ProcessLoop()
@@ -91,6 +124,8 @@ public class LiveCapture : IDisposable
         var tf = new MusicAnalyzer.TickFeature();
         double[]? overlap = null; // last HopSize samples from previous window
 
+        Log("[live] process thread started");
+
         while (_running)
         {
             double[]? windowData = null;
@@ -120,6 +155,8 @@ public class LiveCapture : IDisposable
 
             if (windowData == null)
             {
+                if (_fftCount == 0 && _dataAvailableCount > 0 && _dataAvailableCount % 200 == 0)
+                    Log($"[live] WARNING: data available ({_dataAvailableCount} callbacks, {_totalSamplesReceived} samples) but buffer has only {_sampleBuffer.Count} samples (need {MusicAnalyzer.WindowSize})");
                 Thread.Sleep(5);
                 continue;
             }
@@ -128,6 +165,8 @@ public class LiveCapture : IDisposable
             var spectrum = FFT.Forward(windowData);
             var mag = FFT.Magnitude(spectrum);
 
+            _fftCount++;
+
             var (melodyEnergy, melodyFreq) = MusicAnalyzer.ExtractFeatures(mag, _sampleRate);
 
             // Adaptive normalization: running max with slow decay
@@ -151,6 +190,14 @@ public class LiveCapture : IDisposable
                 _state.EnqueueStream('A', new[] { frameA });
                 _state.EnqueueStream('B', new[] { frameB });
 
+                _tickCount++;
+                if (_tickCount % 50 == 1)
+                {
+                    int intA = (frameA.Intensity[0] + frameA.Intensity[1] + frameA.Intensity[2] + frameA.Intensity[3]) / 4;
+                    int intB = (frameB.Intensity[0] + frameB.Intensity[1] + frameB.Intensity[2] + frameB.Intensity[3]) / 4;
+                    Log($"[live] tick #{_tickCount}: ffts={_fftCount}, melodyEnergy={melodyEnergy:F4}, maxMelody={_liveMaxMelodyEnergy:F4}, freq={melodyFreq:F0}Hz, intA={intA}, intB={intB}, freqA={frameA.Freq[0]}, freqB={frameB.Freq[0]}");
+                }
+
                 tf = new MusicAnalyzer.TickFeature();
                 _fftIndexInTick = 0;
             }