29 lines
1.2 KiB
TypeScript
29 lines
1.2 KiB
TypeScript
import type { Audio } from "../core/types.ts";
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const PEAK_TARGET = Math.pow(10, -1 / 20);
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/** Sum stems (with per-stem gain in dB), then peak-normalise to -1 dBFS. */
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export function mixStems(stems: { audio: Audio; gainDb: number }[]): Audio {
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if (stems.length === 0) throw new Error("mixStems: no stems");
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const sr = stems[0]!.audio.sampleRate;
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const nch = Math.max(...stems.map((s) => s.audio.channels.length));
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const n = Math.max(...stems.map((s) => s.audio.channels[0]?.length ?? 0));
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const out = Array.from({ length: nch }, () => new Float32Array(n));
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for (const { audio, gainDb } of stems) {
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if (audio.sampleRate !== sr) throw new Error("mixStems: sample rate mismatch");
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const g = Math.pow(10, gainDb / 20);
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for (let c = 0; c < nch; c++) {
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const src = audio.channels[c] ?? audio.channels[0]!;
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const dst = out[c]!;
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for (let i = 0; i < src.length; i++) dst[i]! += src[i]! * g;
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}
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}
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let peak = 0;
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for (const ch of out) for (let i = 0; i < n; i++) peak = Math.max(peak, Math.abs(ch[i]!));
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if (peak > 0) {
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const k = PEAK_TARGET / peak;
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for (const ch of out) for (let i = 0; i < n; i++) ch[i]! *= k;
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}
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return { sampleRate: sr, channels: out };
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}
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