function onUpdate(su){
	var speed = su.getSpeed();
	var notch = su.getNotch();
	var maxSp = 130.0;

	if(speed > 0.0){
		var vol = 1.0;
		var s0 = 20;
		if(speed < s0)
		{
			vol = (-((speed - s0) * (speed - s0)) + 10) / 10.0;
		}
		var pitch = (speed / maxSp) * 2.5 - 0.5;
		su.playSound('rtm', 'train.run_trailer', vol, pitch);
	}else{
		su.stopSound('rtm', 'train.run_trailer');
	}
}
