add manual microphone gain and signal meter

public/audio-manager.js

@@ -0,0 +1,68 @@
+export class AudioManager {
+  constructor() {
+    this.context = null;
+    this.rawStream = null;
+    this.outputStream = null;
+    this.source = null;
+    this.gainNode = null;
+    this.analyser = null;
+    this.meterData = new Float32Array(1024);
+    this.gain = Number(localStorage.getItem('voicepoc.micGain') || 1);
+  }
+
+  async ensureContext() {
+    if (!this.context) this.context = new AudioContext();
+    await this.context.resume().catch(() => {});
+    return this.context;
+  }
+
+  async attachInput(stream) {
+    await this.ensureContext();
+    this.detachInput();
+    this.rawStream = stream;
+    this.source = this.context.createMediaStreamSource(stream);
+    this.gainNode = this.context.createGain();
+    this.gainNode.gain.value = this.gain;
+    this.analyser = this.context.createAnalyser();
+    this.analyser.fftSize = 1024;
+    const destination = this.context.createMediaStreamDestination();
+    this.source.connect(this.gainNode).connect(this.analyser);
+    this.gainNode.connect(destination);
+    this.outputStream = destination.stream;
+    return this.outputStream;
+  }
+
+  detachInput() {
+    for (const node of [this.source, this.gainNode, this.analyser]) {
+      try { node?.disconnect(); } catch {}
+    }
+    this.outputStream?.getTracks().forEach((track) => track.stop());
+    this.rawStream?.getTracks().forEach((track) => track.stop());
+    this.source = this.gainNode = this.analyser = null;
+    this.outputStream = this.rawStream = null;
+  }
+
+  setGain(value) {
+    this.gain = Math.max(0, Math.min(2, Number(value) || 0));
+    localStorage.setItem('voicepoc.micGain', String(this.gain));
+    if (this.gainNode) this.gainNode.gain.setTargetAtTime(this.gain, this.context.currentTime, 0.015);
+  }
+
+  getLevel() {
+    if (!this.analyser) return { rms: 0, peak: 0, clipping: false };
+    this.analyser.getFloatTimeDomainData(this.meterData);
+    let sum = 0;
+    let peak = 0;
+    for (const sample of this.meterData) {
+      const magnitude = Math.abs(sample);
+      sum += sample * sample;
+      peak = Math.max(peak, magnitude);
+    }
+    const rms = Math.sqrt(sum / this.meterData.length);
+    return { rms, peak, clipping: peak >= 0.98 };
+  }
+
+  stop() {
+    this.detachInput();
+  }
+}