HP Scanjet 3C as the vocals. It lags a bit due to the fast paced vocals. In order for the stepper motor to play a note it has to be moving and with that large carriage it takes a few milli seconds before it can play a note. It doesn’t sound like a lot of time but stretch that over a 4 minute song and voila…out of sync. Programming does help to compensate but it is not perfect.