We've been asking this for years. It would be great to have a feature in the music player that allows before/after comparisons. Its basically the music version to the "before and after photo slider". The feature would most likely accommodate 2 audio tracks playing simultaneously with selective volume based on which side of the tab the user clicks ("before" tab or "after tab"). *This type of feature would be most useful for music sites that want to showcase before/after comparisons (ex. mixing, mastering, or remix).