Overhaul pitch detection and note matching

- Pick detector per instrument range: ACF2PLUS (robust down to ~40 Hz) for
  normal instruments, YIN only for the whistle register. pitchfinder's YIN
  latches onto tau=2 (~20 kHz garbage) below ~100 Hz and for quiet input;
  the old fixed 4096 window masked this, the smaller window exposed it.
- RMS-normalize analysis input for the YIN path only; ACF2PLUS keeps the raw
  signal so its internal unpitched gate rejects quiet decayed audio instead
  of amplifying noise into confident wrong pitches (tuner stuck on 'a note').
- Adaptive analysis window sized to the instrument's lowest note (~2 periods):
  half the latency, a quarter of the CPU for guitar/piano/voice; bass keeps
  the full window for E1.
- Reject detections implausibly below the instrument floor (mains hum).
- Clear stale pitch readings after 200 ms instead of keeping them forever.
- Shared AudioEngine singleton for all playback (was: two AudioContexts);
  tracks audibility so the app stops hearing its own speaker (ear-training
  self-scoring) and gates matching plus display during playback.
- MatchTracker: grace-period based note hold instead of reset-on-every-flicker
  (YIN flickers during attacks/decays; the old hard reset made the 50 ms
  threshold fire unreliably).
- Display damping in the producer (EMA for cents/level, 3-frame note-name
  hysteresis); display components render directly without CSS transitions.
- Regression tests: synthetic signals through the exact pipeline helpers
  (MatchTracker + pitchDetection test suites).

src/hooks/useAudioPlayer.ts

@@ -1,61 +1,18 @@
-import { useRef, useEffect, useCallback } from 'react';
-import { midiToFrequency } from '../music/NoteUtils';
+import { useCallback } from 'react';
+import { audioEngine } from '../audio/AudioEngine';
 
 interface AudioPlayerHandle {
     playNote: (midi: number, duration?: number, volume?: number) => void;
 }
 
+/**
+ * Thin hook wrapper around the shared AudioEngine singleton.
+ * All playback goes through one AudioContext and is tracked there, so pitch
+ * detection can gate itself while the app's own speaker output is audible.
+ */
 export function useAudioPlayer(): AudioPlayerHandle {
-    const audioContext = useRef<AudioContext | null>(null);
-
-    // Initialize AudioContext lazily or on user interaction if possible, 
-    // but here we just ensure it exists when we try to play.
-
     const playNote = useCallback((midi: number, duration: number = 0.5, volume: number = 0.3) => {
-        if (!audioContext.current) {
-            audioContext.current = new (window.AudioContext || (window as any).webkitAudioContext)();
-        }
-
-        const ctx = audioContext.current;
-        if (ctx.state === 'suspended') {
-            ctx.resume();
-        }
-
-        const osc = ctx.createOscillator();
-        const gainNode = ctx.createGain();
-
-        const freq = midiToFrequency(midi);
-
-        osc.frequency.value = freq;
-        // Triangle wave is often nicer than sine for music training
-        osc.type = 'triangle';
-
-        osc.connect(gainNode);
-        gainNode.connect(ctx.destination);
-
-        const now = ctx.currentTime;
-
-        // Attack
-        gainNode.gain.setValueAtTime(0, now);
-        gainNode.gain.linearRampToValueAtTime(volume, now + 0.02);
-
-        // Sustain -> Release
-        // Note: For a "pluck" or single hit, we just ramp down.
-        gainNode.gain.exponentialRampToValueAtTime(0.001, now + duration);
-
-        osc.start(now);
-        osc.stop(now + duration + 0.1); // Stop slightly after fade out
-
-    }, []);
-
-    // Cleanup
-    useEffect(() => {
-        return () => {
-            if (audioContext.current) {
-                audioContext.current.close();
-                audioContext.current = null;
-            }
-        };
+        audioEngine.playNote(midi, duration, volume);
     }, []);
 
     return { playNote };