Tim Bowen sheds some light on the origins and definition of the phrase to face the music.

Sometimes, when you have done something wrong, it’s better to accept the consequences rather than try and avoid them. For example, a student who has failed to submit an assignment on time may say to a colleague "Right. I’d better go and face the music", meaning that he will go and meet the lecturer or teacher involved and face the inevitable criticism or punishment that will follow.

The expression probably has military origins. When soldiers were dismissed from the army for some misdemeanour or other, it was standard practice for an official ceremony to accompany their departure. The unfortunate victim would depart from the camp or barracks by enduring a ‘walk of shame’ past the ranks of his fellow soldiers. The ‘walk of shame’ was usually accompanied by the beat of a drum, hence the association of music with the idea of accepting one’s punishment.