fix: tempo octave choice, start-of-music anchoring, mean-normalised combs, pure toMono

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/audio/wav.ts

@@ -67,16 +67,7 @@ export async function writeWav(path: string, a: Audio): Promise<void> {
   await Bun.write(path, out);
 }
 
-/** Average all channels into one mono signal. */
-export function toMono(a: Audio): Float32Array {
-  const n = a.channels[0]?.length ?? 0;
-  if (a.channels.length === 1) return a.channels[0]!.slice();
-  const out = new Float32Array(n);
-  for (const ch of a.channels) for (let i = 0; i < n; i++) out[i]! += ch[i]!;
-  const k = 1 / a.channels.length;
-  for (let i = 0; i < n; i++) out[i]! *= k;
-  return out;
-}
+export { toMono } from "../dsp/mono.ts";
 
 const sinc = (x: number) => (x === 0 ? 1 : Math.sin(Math.PI * x) / (Math.PI * x));