1 files changed, 103 insertions, 0 deletions
diff --git a/apps/web/src/media/audio-mastering.ts b/apps/web/src/media/audio-mastering.ts
new file mode 100644
index 00000000..f901c3bf
--- /dev/null
+++ b/apps/web/src/media/audio-mastering.ts
@@ -0,0 +1,103 @@
+const MASTER_LIMITER_THRESHOLD_DB = -1;
+const MASTER_LIMITER_KNEE_DB = 0;
+const MASTER_LIMITER_RATIO = 20;
+const MASTER_LIMITER_ATTACK_SECONDS = 0.001;
+const MASTER_LIMITER_RELEASE_SECONDS = 0.12;
+const MASTER_OUTPUT_HEADROOM = 0.98;
+
+export function getAudioBufferPeak({
+	audioBuffer,
+}: {
+	audioBuffer: AudioBuffer;
+}): number {
+	let peak = 0;
+
+	for (let channel = 0; channel < audioBuffer.numberOfChannels; channel++) {
+		const channelData = audioBuffer.getChannelData(channel);
+		for (let index = 0; index < channelData.length; index++) {
+			const magnitude = Math.abs(channelData[index]);
+			if (magnitude > peak) {
+				peak = magnitude;
+			}
+		}
+	}
+
+	return peak;
+}
+
+export function createAudioMasteringChain({
+	audioContext,
+	destination,
+}: {
+	audioContext: AudioContext | OfflineAudioContext;
+	destination: AudioNode;
+}): {
+	input: GainNode;
+} {
+	const input = audioContext.createGain();
+	const limiter = audioContext.createDynamicsCompressor();
+	const outputGain = audioContext.createGain();
+
+	limiter.threshold.value = MASTER_LIMITER_THRESHOLD_DB;
+	limiter.knee.value = MASTER_LIMITER_KNEE_DB;
+	limiter.ratio.value = MASTER_LIMITER_RATIO;
+	limiter.attack.value = MASTER_LIMITER_ATTACK_SECONDS;
+	limiter.release.value = MASTER_LIMITER_RELEASE_SECONDS;
+	outputGain.gain.value = MASTER_OUTPUT_HEADROOM;
+
+	input.connect(limiter);
+	limiter.connect(outputGain);
+	outputGain.connect(destination);
+
+	return { input };
+}
+
+export async function applyAudioMasteringToBuffer({
+	audioBuffer,
+}: {
+	audioBuffer: AudioBuffer;
+}): Promise<AudioBuffer> {
+	if (getAudioBufferPeak({ audioBuffer }) <= MASTER_OUTPUT_HEADROOM) {
+		return audioBuffer;
+	}
+
+	const offlineContext = new OfflineAudioContext(
+		audioBuffer.numberOfChannels,
+		Math.max(1, audioBuffer.length),
+		audioBuffer.sampleRate,
+	);
+	const source = offlineContext.createBufferSource();
+	source.buffer = audioBuffer;
+
+	const { input } = createAudioMasteringChain({
+		audioContext: offlineContext,
+		destination: offlineContext.destination,
+	});
+	source.connect(input);
+	source.start(0);
+
+	const renderedBuffer = await offlineContext.startRendering();
+	clampAudioBufferPeak({
+		audioBuffer: renderedBuffer,
+		maxPeak: MASTER_OUTPUT_HEADROOM,
+	});
+	return renderedBuffer;
+}
+
+function clampAudioBufferPeak({
+	audioBuffer,
+	maxPeak,
+}: {
+	audioBuffer: AudioBuffer;
+	maxPeak: number;
+}): void {
+	for (let channel = 0; channel < audioBuffer.numberOfChannels; channel++) {
+		const channelData = audioBuffer.getChannelData(channel);
+		for (let index = 0; index < channelData.length; index++) {
+			channelData[index] = Math.max(
+				-maxPeak,
+				Math.min(maxPeak, channelData[index]),
+			);
+		}
+	}
+}