This corner pillar of the temple is carved out of a single stone. The seven small struts are in different diameters and are arranged to give the seven notes (Sa, re, ga, ma pa, dha, ni sa) These are the Do-re-mi-fa-so-la-tee of Indian Music. With a wooden rod an expert can play any tune on this pillar. I have seen some of them producing music with bare hands.
Incidentally musical pillar is not unique to Hampi. Such pillars are available in almost all ancient South Indian temples like Kancheepuram, Chidambaram, Madurai Meenakshi etc.