JSSoundRecorder

Update 2025/11/30: after more than a decade, I decided to update the app and make it work again with current browsers! Also updated the outdated snippets below, but left the rest mostly the same.

Record sounds / noises around you and turn them into music.

It’s a work in progress, at the moment it enables you to record live audio straight from your browser, edit it and save these sounds as a WAV file.

There's also a sequencer part where you can create small loops using these sounds with a drone synth overlaid on them.

See it working: https://daaain.github.io/JSSoundRecorder

Technology

No servers involved, only Web Audio API with binary sound Blobs passed around!

Web Audio API

GetUserMedia audio for live recording

Experimental API to record any system audio input (including USB soundcards, musical instruments, etc).

// create AudioContext and request microphone access
var audio_context = new AudioContext();

const stream = await navigator.mediaDevices.getUserMedia({audio: true});
startUserMedia(stream);

Audio nodes for routing

You can route audio stream around, with input nodes (microphone, synths, etc), filters (volume / gain, equaliser, low pass, etc) and outputs (speakers, binary streams, etc).

function startUserMedia(stream) {
  // create MediaStreamSource and GainNode
  var input = audio_context.createMediaStreamSource(stream);
  var volume = audio_context.createGain();
  volume.gain.value = 0.7;

  // connect them and pipe output
  input.connect(volume);
  volume.connect(audio_context.destination);
  
  // connect recorder as well - see below
  var recorder = new Recorder(input);
}

AudioWorklet + WebWorker

Audio capture uses AudioWorklet (runs on the audio rendering thread for glitch-free recording), while heavy processing (interleaving, WAV encoding) is done in a WebWorker to not block the main thread.

// Register AudioWorklet for capturing audio
this.context.audioWorklet.addModule('js/lib/recorder-worklet.js').then(function() {
  self.node = new AudioWorkletNode(self.context, 'recorder-worklet');

  // Forward audio data from worklet to worker for processing
  self.node.port.onmessage = function(e) {
    if (e.data.command === 'audioData') {
      worker.postMessage({
        command: 'record',
        buffer: e.data.buffer
      });
    }
  };

  source.connect(self.node);
});

function record(inputBuffer){
  var bufferL = inputBuffer[0];
  var bufferR = inputBuffer[1];
  var interleaved = interleave(bufferL, bufferR);
  recBuffers.push(interleaved);
  recLength += interleaved.length;
}

function interleave(inputL, inputR){
  var length = inputL.length + inputR.length;
  var result = new Float32Array(length);

  var index = 0,
      inputIndex = 0;

  while (index < length){
    result[index++] = inputL[inputIndex];
    result[index++] = inputR[inputIndex];
    inputIndex++;
  }
  return result;
}

function encodeWAV(samples){
  var buffer = new ArrayBuffer(44 + samples.length * 2);
  var view = new DataView(buffer);

  /* RIFF identifier */
  writeString(view, 0, 'RIFF');
  /* file length */
  view.setUint32(4, 32 + samples.length * 2, true);
  /* RIFF type */
  writeString(view, 8, 'WAVE');
  /* format chunk identifier */
  writeString(view, 12, 'fmt ');
  /* format chunk length */
  view.setUint32(16, 16, true);
  /* sample format (raw) */
  view.setUint16(20, 1, true);
  /* channel count */
  view.setUint16(22, 2, true);
  /* sample rate */
  view.setUint32(24, sampleRate, true);
  /* byte rate (sample rate * block align) */
  view.setUint32(28, sampleRate * 4, true);
  /* block align (channel count * bytes per sample) */
  view.setUint16(32, 4, true);
  /* bits per sample */
  view.setUint16(34, 16, true);
  /* data chunk identifier */
  writeString(view, 36, 'data');
  /* data chunk length */
  view.setUint32(40, samples.length * 2, true);

  floatTo16BitPCM(view, 44, samples);

  return view;
}

Binary Blob

Instead of file drag and drop interface this binary blob is passed to editor.

Note: BlobBuilder deprecated (but a lot of examples use it), you should use Blob constructor instead!

var f = new FileReader();
f.onload = function(e) {
  audio_context.decodeAudioData(e.target.result, function(buffer) {
      $('#audioLayerControl')[0].handleAudio(buffer);
    }, function(e) {
      console.warn(e);
    });
  };
f.readAsArrayBuffer(blob);

function exportWAV(type){
  var buffer = mergeBuffers(recBuffers, recLength);
  var dataview = encodeWAV(buffer);
  var audioBlob = new Blob([dataview], { type: type });

  this.postMessage(audioBlob);
}

Virtual File – URL.createObjectURL

You can create file download link pointing to WAV blob, but also set it as the source of an Audio element.

var url = URL.createObjectURL(blob);
var audioElement = document.createElement('audio');
var downloadAnchor = document.createElement('a');

audioElement.controls = true;
audioElement.src = url;

downloadAnchor.href = url;

TODO

• Sequencer top / status row should be radio buttons :)
• Code cleanup / restructuring
• Enable open / drag and drop files for editing
• Visual feedback (levels) for live recording
• Sequencer UI (and separation to a different module)

Credits

Live recording code adapted from: http://www.phpied.com/files/webaudio/record.html

Editor code adapted from: https://github.com/plucked/html5-audio-editor