code: void update(int delta) {
  		if (!playing) {
  			return;
  		}
         
  		if (fadeTime > 0) {
  			fadeTime -= delta;
  			if (fadeTime <= 0) {
  				fadeTime = 0;
  				if (stopAfterFade) {
  					stop();
  					return;
  				}
  			}
  			
  			float offset = (fadeEndGain - fadeStartGain) * (1 - (fadeTime / (float)fadeDuration));
  			setVolume(fadeStartGain + offset);
  		}
  	}
docs: Update the current music applying any effects that need to updated per
  tick.
  
  @param delta The amount of time in milliseconds thats passed since last update