sonic-wasm

WebAssembly bindings for libsonic - a fast, high-quality audio time-stretching and pitch-shifting library.

Features

• Time-stretch audio without changing pitch (speed up/slow down)
• Pitch-shift audio without changing duration
• Low latency (~20-30ms) suitable for real-time TTS streaming
• Zero dependencies - WASM is bundled
• Works with Node.js and Bun

Installation

bun add sonic-wasm
# or
npm install sonic-wasm

Quick Start

import { Sonic } from "sonic-wasm";

// Create a processor for 24kHz mono audio at 1.5x speed
const sonic = await Sonic.create({
  sampleRate: 24000,
  numChannels: 1,
  speed: 1.5,
});

// Process audio (Float32Array)
const output = sonic.process(inputSamples);

// Flush remaining samples when done
const remaining = sonic.flush();

// Clean up
sonic.destroy();

API

Sonic.create(options)

Creates a new Sonic processor instance.

interface SonicOptions {
  sampleRate: number;      // Sample rate in Hz (e.g., 24000, 44100)
  numChannels?: number;    // Number of channels (default: 1)
  speed?: number;          // Playback speed (default: 1.0)
  pitch?: number;          // Pitch factor (default: 1.0)
  rate?: number;           // Rate factor (default: 1.0)
  volume?: number;         // Volume (default: 1.0)
}

const sonic = await Sonic.create(options);

sonic.process(input: Float32Array): Float32Array

Process audio samples. Returns time-stretched/pitch-shifted output.

For streaming, call repeatedly with chunks of audio. Output length varies based on speed setting.

sonic.flush(): Float32Array

Flush any remaining buffered samples. Call this when you're done processing to get the final audio.

sonic.setSpeed(speed: number)

Change playback speed without affecting pitch.

• 0.5 = half speed (slower)
• 1.0 = normal speed
• 2.0 = double speed (faster)

Range: 0.05 to 20.0

sonic.setPitch(pitch: number)

Change pitch without affecting duration.

• 0.5 = one octave down
• 1.0 = normal pitch
• 2.0 = one octave up

Range: 0.05 to 20.0

sonic.setRate(rate: number)

Change both speed and pitch together (like changing tape speed).

sonic.setVolume(volume: number)

Adjust output volume. 1.0 = normal.

sonic.setQuality(quality: 0 | 1)

• 0 = optimized for low latency
• 1 = optimized for higher quality

sonic.samplesAvailable(): number

Returns the number of output samples available to read.

sonic.destroy()

Free all resources. Must be called when done.

Examples

Speed Up TTS Audio

import { Sonic } from "sonic-wasm";

const sonic = await Sonic.create({
  sampleRate: 24000,
  speed: 1.3, // 30% faster
});

const spedup = sonic.process(ttsAudio);
const final = sonic.flush();

sonic.destroy();

Streaming (Low Latency)

Process audio in small chunks for real-time applications:

import { Sonic } from "sonic-wasm";

const sonic = await Sonic.create({
  sampleRate: 24000,
  speed: 1.5,
});

// Process 20ms chunks as they arrive
const chunkSize = 480; // 20ms at 24kHz

for (const chunk of audioChunks) {
  const output = sonic.process(chunk);
  if (output.length > 0) {
    playAudio(output);
  }
}

// Don't forget final samples
const remaining = sonic.flush();
if (remaining.length > 0) {
  playAudio(remaining);
}

sonic.destroy();

Pitch Shift Without Speed Change

import { Sonic } from "sonic-wasm";

const sonic = await Sonic.create({
  sampleRate: 44100,
  speed: 1.0,  // Keep original duration
  pitch: 1.5, // Shift pitch up ~7 semitones
});

const pitched = sonic.process(audio);
const final = sonic.flush();

sonic.destroy();

Dynamic Speed Adjustment

import { Sonic } from "sonic-wasm";

const sonic = await Sonic.create({ sampleRate: 24000 });

// Start at normal speed
sonic.setSpeed(1.0);
let output1 = sonic.process(chunk1);

// Speed up mid-stream
sonic.setSpeed(2.0);
let output2 = sonic.process(chunk2);

sonic.destroy();

Building from Source

Requires Emscripten to rebuild the WASM.

# Install Emscripten (one-time)
git clone https://github.com/emscripten-core/emsdk.git
cd emsdk && ./emsdk install latest && ./emsdk activate latest
source emsdk_env.sh

# Build
bun run build

License

Apache-2.0 (same as libsonic)