deja entendu's dashboard

in tap tap when is the perfect time to tap on the beat? i know the tutorial says when its passing the white line... is there a more exact moment that could be given? i noticed that you receive a different score on each beat [50,75,150] for how accurate you are to the exact moment you're supposed to tap; i believe the multipliers also rely on syncing the perfect tap on beat for a number of times[knowing how many perfect taps it takes to receive a multiplier would be helpful as well]. just a little more clarity about timing would be great along with a more thorough tutorial.