Simple example of how to get audio data from live microphone input via getUserMedia.

gistfile1.js

window.onload = function() {
  var context = new webkitAudioContext();
	var analyser = context.createAnalyser();
	var buffer = new Float32Array(analyser.frequencyBinCount);

	function analyze() {
		requestAnimationFrame(analyze);
		analyser.getFloatFrequencyData(buffer);
		// buffer is now filled with data
		// if there are -100 values only set your systems microphone & speakers sample rates to the same values
		console.log(buffer[0]);
	}

	function connectStream(stream) {
		// uncomment if you want to playback the recorded audio too
		//var audioElement = document.getElementById('audio');
		//audioElement.autoplay = true;
		//audioElement.src = window.webkitURL.createObjectURL(stream);

		var source = context.createMediaStreamSource(stream);
		source.connect(analyser);
		analyze();
	}

	function microphoneError(e) {
		alert('MicrophoneError error!', e);
	};

	if (navigator.webkitGetUserMedia) {
		navigator.webkitGetUserMedia({audio: true, video: false}, connectStream, microphoneError);
	} else {
		alert('Your browser does not support webkitGetUserMedia.');
	}
};