web-bpm v0.2.1

Web BPM

Compute beats per minute and register listeners on kick from an audio input

API

getUserInput

const getUserInput: (fftSize: number) => Promise<AnalyserNode>

Captures the browser's microphone audio stream

You might see the browser asking the user for audio recording permission on the first function call

fftSize is passed to AnalyserNode.fftSize and thus should be a power of two between 2^5 and 2^15

import { getUserInput } from 'https://cdn.skypack.dev/web-bpm';

(async () => {
	const analyser = await getUserInput(512);
  console.log(analyser);
})();

Fiddle link

createKickDetector

const createKickDetector: (analyser: AnalyserNode) => {
  threshold: number;
  up: number;
  smooth: number;
  onKick: () => void;
  listen: () => void;
  stop: () => void;
}

Triggers a listener on kick

This doesn't analyses BPM, but rather measures the average rise of volume over all frequencies, smoothes it out (smooth = 0 for no smoothing, smooth = 1 for constant output), stores in it up, and if it's greater than threshold, calls back onKick.

listen() starts listening, stop() stops listening.

import { getUserInput, createKickDetector } from 'web-bpm';

(async () => {
  const analyser = await getUserInput(512);
  const kickDetector = createKickDetector(analyser);
  kickDetector.threshold = 0.01;
  kickDetector.smooth = 0.8;
  kickDetector.onKick = () => console.log('kick');
  kickDetector.listen();
  setTimeout(() => kickDetector.stop(), 10000);
})();

Fiddle link