getdecibel.js

	var audioCtx = new (window.AudioContext || window.webkitAudioContext)();
	var source;

	var analyser = audioCtx.createAnalyser();
	analyser.minDecibels = -60.0;
	analyser.maxDecibels = 0.0;
	analyser.smoothingTimeConstant = 0.8;
	analyser.fftSize = 128;

	var javascriptNode = audioCtx.createScriptProcessor(1024);
	javascriptNode.onaudioprocess = function(evt) {
		var array = new Float32Array(analyser.frequencyBinCount);
		analyser.getFloatFrequencyData(array);
		var bufLength = array.length;
		var db;
		var sum = 0;
		var peak = 0;

		for (var i = 0; i < bufLength; i++) {
			db = array[i]; // - analyser.minDecibels;
			sum += (db * db);
			peak = Math.max(db, peak);
		}
		var rms = Math.sqrt(sum / bufLength);
		javascriptNode.dbVolume = rms;
	};

	var drawMicVolume = function(timestamp) {
		console.log(javascriptNode.dbVolume);
		requestAnimationFrame(drawMicVolume);
	};
	
	if (navigator.mediaDevices && navigator.mediaDevices.getUserMedia) {
		navigator.mediaDevices.getUserMedia({ audio: true}).then(function(stream) {
			source = audioCtx.createMediaStreamSource(stream);
			source.connect(analyser);
			source.connect(javascriptNode);
			// analyser.connect(audioCtx.destination);
			requestAnimationFrame(drawMicVolume);
		}).catch(function(err) {
			console.error("The following getUserMedia error occured: " + err);
		});
	} else {
		console.error("navigator.mediaDevices.getUserMedia does not exist.");
	}