@playground-sessions/amdf-js

A pure JavaScript implementation of the Average Magnitude Difference Function (AMDF) for pitch detection. This package provides a straightforward, educational implementation with adjustable frame sizes and downsampling options.

Features

• Pure JavaScript implementation (no WebAssembly)
• Configurable frame sizes and downsampling factors
• Adjustable frequency range
• Clarity metric for pitch confidence
• TypeScript types included
• Zero dependencies

Installation

npm install @playground-sessions/amdf-js

Usage

import { AmdfPitchDetector } from '@playground-sessions/amdf-js';

// Create a detector with custom options
const detector = new AmdfPitchDetector({
  frameSize: 2048,          // Must be a power of 2
  sampleRate: 44100,        // Audio sample rate
  minFrequency: 50,         // Lowest frequency to detect
  maxFrequency: 2000,       // Highest frequency to detect
  downsampleFactor: 1       // Optional downsampling (must be power of 2)
});

// Analyze a frame of audio
const frame = new Float32Array(2048); // Your audio data here
const result = detector.analyze(frame);
console.log(`Frequency: ${result.frequency} Hz`);
console.log(`Clarity: ${result.clarity}`);

Demo

A live demo is included in the package. To run it:

1. Clone this repository
2. Run npm install
3. Run npm run dev
4. Open your browser and try the interactive pitch detector

How it Works

The Average Magnitude Difference Function (AMDF) is a time-domain pitch detection algorithm that works by:

1. Comparing a signal with delayed versions of itself
2. Finding the delay (lag) that produces the minimum difference
3. Converting that lag into a frequency

The implementation is intentionally straightforward for learning purposes, making it a good starting point for understanding pitch detection algorithms.

Options

• frameSize: Size of the analysis frame (default: 2048)
• sampleRate: Sample rate of the audio (default: 44100)
• minFrequency: Minimum frequency to detect (default: 50 Hz)
• maxFrequency: Maximum frequency to detect (default: 2000 Hz)
• downsampleFactor: Factor to downsample by (default: 1)

Contributing

Contributions are welcome! This is an educational project built during the WebAudio Pitch Jam '25.