function gotStream(stream) {
    window.AudioContext = window.AudioContext || window.webkitAudioContext;
    var audioContext = new AudioContext();

    // Create an AudioNode from the stream
    var mediaStreamSource = audioContext.createMediaStreamSource(stream);

    // Connect it to destination to hear yourself
    // or any other node for processing!
    mediaStreamSource.connect(audioContext.destination);
}

navigator.getUserMedia({audio:true}, gotStream);