fix: rebalance procedural audio mix

src/audio/synth-engine.ts

@@ -54,7 +54,7 @@ export function createSynthEngine(createContext: AudioContextFactory): AudioGrap
   musicFilter.frequency.setValueAtTime(900, context.currentTime);
   musicFilter.Q.setValueAtTime(0.72, context.currentTime);
   const musicGain = context.createGain();
-  musicGain.gain.setValueAtTime(0.38, context.currentTime);
+  musicGain.gain.setValueAtTime(0.78, context.currentTime);
   musicFilter.connect(musicGain);
   musicGain.connect(dynamics);
 
@@ -64,7 +64,7 @@ export function createSynthEngine(createContext: AudioContextFactory): AudioGrap
   engineFilter.Q.setValueAtTime(1.25, context.currentTime);
 
   const engineGain = context.createGain();
-  engineGain.gain.setValueAtTime(0.24, context.currentTime);
+  engineGain.gain.setValueAtTime(0.09, context.currentTime);
   engineFilter.connect(engineGain);
   engineGain.connect(dynamics);
 
@@ -76,7 +76,7 @@ export function createSynthEngine(createContext: AudioContextFactory): AudioGrap
   roadFilter.frequency.setValueAtTime(410, context.currentTime);
   roadFilter.Q.setValueAtTime(0.55, context.currentTime);
   const roadGain = context.createGain();
-  roadGain.gain.setValueAtTime(0.045, context.currentTime);
+  roadGain.gain.setValueAtTime(0.018, context.currentTime);
   roadFilter.connect(roadGain);
   roadGain.connect(dynamics);
 
@@ -90,7 +90,7 @@ export function createSynthEngine(createContext: AudioContextFactory): AudioGrap
   ignition.frequency.setValueAtTime(68, context.currentTime);
   const ignitionGain = context.createGain();
   ignitionGain.gain.setValueAtTime(0.0001, context.currentTime);
-  ignitionGain.gain.exponentialRampToValueAtTime(0.07, context.currentTime + 0.12);
+  ignitionGain.gain.exponentialRampToValueAtTime(0.025, context.currentTime + 0.12);
   ignitionGain.gain.exponentialRampToValueAtTime(0.0001, context.currentTime + 1.15);
   ignition.connect(ignitionGain);
   ignitionGain.connect(engineFilter);
@@ -154,8 +154,8 @@ export function createSynthEngine(createContext: AudioContextFactory): AudioGrap
       engineFilter.frequency.setTargetAtTime(260 + next * 670, time, 0.38);
       roadFilter.frequency.setTargetAtTime(410 + next * 520, time, 0.42);
       musicFilter.frequency.setTargetAtTime(900 + next * 2_400, time, 0.42);
-      engineGain.gain.setTargetAtTime(0.24 + next * 0.12, time, 0.4);
-      roadGain.gain.setTargetAtTime(0.045 + next * 0.06, time, 0.45);
+      engineGain.gain.setTargetAtTime(0.09 + next * 0.04, time, 0.4);
+      roadGain.gain.setTargetAtTime(0.018 + next * 0.02, time, 0.45);
       music.setIntensity(next, time);
     },
     onContextStateChange(listener) {

tests/unit/audio-lifecycle.test.ts

@@ -212,6 +212,29 @@ describe('audio controller lifecycle', () => {
 });
 
 describe('procedural audio graph', () => {
+  it('keeps the soundtrack clearly ahead of the ambient drive effects across intensity changes', async () => {
+    vi.useFakeTimers();
+    const context = new FakeAudioContext();
+
+    try {
+      const graph = createSynthEngine(() => context as unknown as AudioContext);
+      const [, musicGain, engineGain, , , roadGain, ignitionGain] = context.gains;
+
+      expect(musicGain?.gain.value).toBe(0.78);
+      expect(engineGain?.gain.value).toBe(0.09);
+      expect(roadGain?.gain.value).toBe(0.018);
+      expect(ignitionGain?.gain.scheduledValues).toEqual([0.0001, 0.025, 0.0001]);
+
+      graph.setIntensity(1);
+      expect(engineGain?.gain.targetValues).toContain(0.13);
+      expect(roadGain?.gain.targetValues).toContain(0.038);
+
+      await graph.close();
+    } finally {
+      vi.useRealTimers();
+    }
+  });
+
   it('routes independent music, engine, and road buses through compression before the master output', async () => {
     vi.useFakeTimers();
     const context = new FakeAudioContext();