Tone.js/test/helper/Meter.js

define(["helper/Offline"], function(Offline) {

	return function(callback, duration, channels){

		return Offline(callback, duration, channels).then(function(buffer){
			var rms = buffer.getRMS(512);
			rms.forEach = function(callback){
				for (var i = 0; i < rms.length; i++){
					var level = rms[i];
					callback(level, i * buffer.sampleTime);
				}
			};
			rms.getValueAtTime = function(time){
				return rms[Math.floor(time * buffer.context.sampleRate)];
			};
			return rms;
		});
	};
});