# Audio Peak Measurement Fix Summary

## Issues Found and Fixed

### Issue #1: Peak Measured at Wrong Time (❌ FIXED)
**Problem:** Peak was measured when audio was written to ring buffer (~400ms before playback), causing visual effects to trigger 400ms early.

**Solution:**
- Added `get_realtime_peak()` to AudioBackend interface
- Implemented real-time peak measurement in audio callback when samples are actually played
- Updated main.cc and test_demo.cc to use `audio_get_realtime_peak()` instead of `synth_get_output_peak()`

**Files Modified:**
- src/audio/audio_backend.h
- src/audio/miniaudio_backend.h/cc
- src/audio/mock_audio_backend.h/cc
- src/audio/wav_dump_backend.h/cc
- src/audio/jittered_audio_backend.h/cc
- src/audio/audio.h/cc
- src/main.cc
- src/test_demo.cc
- src/tests/test_audio_backend.cc

### Issue #2: Peak Decay Too Slow (❌ FIXED)
**Problem:** Peak decay rate of 0.95 per callback meant visual effects stayed bright for ~6 seconds after a drum hit, causing constant flashing.

**Root Cause Analysis:**
- Decay rate: 0.95 per callback
- Callback interval: ~128ms
- Time to decay to 10%: **~5.76 seconds** (45 callbacks)
- Result: Screen stays white for 6+ seconds after each drum hit

**Solution:**
- Changed decay rate from 0.95 to 0.7
- New decay timing:
  - 50% intensity: ~256ms (2 callbacks)
  - 10% intensity: ~1.15 seconds (9 callbacks)
- Result: Quick flash with smooth fade, proper visual sync

**Decay Comparison:**
```
Old (0.95):  ████████████████████████████ (6 seconds to fade)
New (0.7):   ████ (1 second to fade)
```

**File Modified:**
- src/audio/miniaudio_backend.cc (line 164)

## Verification

✅ All 27 tests pass
✅ demo64k builds successfully
✅ test_demo builds successfully
✅ Peak decay timing verified mathematically
✅ Audio-visual sync should now be accurate

## Testing Instructions

Run test_demo to verify the fix:
```bash
./build/test_demo
```

Expected behavior:
- Screen should flash white on drum hits (every ~0.5 seconds)
- Flash should fade quickly (~1 second)
- No constant white screen
- Audio and visual should be synchronized

## Known Build Issues (Pre-existing)

The following tests have linker errors (unrelated to peak measurement fix):
- test_effect_base (missing WebGPUTestFixture)
- test_post_process_helper (missing main)
- test_texture_manager (missing main)
- test_demo_effects (missing main)

These appear to be incomplete test implementations and should be addressed separately.