function onTap(){

		//start the audio context with a silent oscillator
		if (StartAudioContext.context && !StartAudioContext.isStarted()){
			var osc = StartAudioContext.context.createOscillator();
			var silent = StartAudioContext.context.createGain();
			silent.gain.value = 0;
			osc.connect(silent);
			silent.connect(StartAudioContext.context.destination);
			var now = StartAudioContext.context.currentTime;
			osc.start(now);
			osc.stop(now+0.5);
		}

		//dispose all the tap listeners
		if (StartAudioContext._tapListeners){
			for (var i = 0; i < StartAudioContext._tapListeners.length; i++){
				StartAudioContext._tapListeners[i].dispose();
			}
			StartAudioContext._tapListeners = null;
		}
		//the onstarted callbacks
		if (StartAudioContext._onStarted){
			for (var j = 0; j < StartAudioContext._onStarted.length; j++){
				StartAudioContext._onStarted[j]();
			}
			StartAudioContext._onStarted = null;
		}
	}
Invoked the first time of the elements is tapped.
Creates a silent oscillator when a non-dragging touchend 
event has been triggered.