The medieval musicians improvise, which means adding and changing musical materials as he or she performed a piece. The kind of instrument or voice to be used, the pitches in the melody, the kind of accompaniment might vary from one time to the next and so do the tempo, the volume, and the rhythm. The music ranges from the sacred to the wicked and from a solo with a single melody sung alone to the richly voices of several working all together. The church, the court, the university, the town, and the tavern have all contributed evidently to music. The most serious music, both sacred and secular, was song, involving words as an important part.