x-law

A-Law, μ-Law and common audio utilites for JavaScript/TypeScript

This package started as a rewrite of the alawmulaw library in TypeScript for a modernized build process and updated dependencies. It adds additional utilities and features for processing audio data, such as loudness calculation, more flexible encoding/decoding, and more.

Primarily intended for use in a backend environment.

Install

npm install x-law
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Usage

CommonJS:

const { alaw, mulaw, utils } = require("x-law");
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ESM:

import { alaw, mulaw, utils } from "x-law";
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Examples

Basic Usage

import { alaw, mulaw } from "x-law";

// Convert between PCM and μ-Law/A-Law
const pcmSamples = new Int16Array([
  /* 16-bit PCM samples */
]);

// Encode to μ-Law
const mulawSamples = mulaw.encode(pcmSamples); // Returns Uint8Array
// Decode back to PCM
const decodedPcm = mulaw.decode(mulawSamples); // Returns Int16Array

// Encode to A-Law
const alawSamples = alaw.encode(pcmSamples); // Returns Uint8Array
// Decode back to PCM
const decodedAlawPcm = alaw.decode(alawSamples); // Returns Int16Array

// Working with Buffer objects
const pcmBuffer = Buffer.from(pcmSamples.buffer);
const encodedMulaw = mulaw.encodeBuffer(pcmBuffer);
const decodedBuffer = mulaw.decodeBuffer(encodedMulaw);
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Single Sample Processing

import { alaw, mulaw } from "x-law";

// Single sample conversion
const pcmSample = 16384; // 16-bit PCM sample
const mulawSample = mulaw.encodeSample(pcmSample);
const decodedSample = mulaw.decodeSample(mulawSample);

const alawSample = alaw.encodeSample(pcmSample);
const decodedAlawSample = alaw.decodeSample(alawSample);
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Audio Processing Utilities

import { utils } from "x-law";

// Calculate RMS loudness in decibels
const buffer = Buffer.from(/* PCM audio data */);
const loudness = utils.calculateLoudness(buffer, 16); // For 16-bit PCM
console.log(`RMS Loudness: ${loudness} dB`);

// Resample audio (e.g., from 48kHz to 16kHz)
const samples = [
  /* PCM samples */
];
const resampled = utils.resample(samples, 48000, 16000, 16); // 16-bit depth

// Create a WAV header for audio data
const dataSize = pcmSamples.byteLength;
const wavHeader = utils.createWavHeader(
  dataSize, // Size of audio data in bytes
  44100, // Sample rate (Hz)
  1, // Channels (1 = mono, 2 = stereo)
  16 // Bit depth (8, 16, 24, or 32)
);

// Write WAV file
const wavFile = Buffer.concat([wavHeader, Buffer.from(pcmSamples.buffer)]);
fs.writeFileSync("output.wav", wavFile);
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You can find the full documentation here.

Contributing

Contributions are welcome! See CONTRIBUTING.md for more details.

LICENSE

This project is licensed under the MIT license. See LICENSE for more details.