Shruti box

A shruti box (sruti box or surpeti) is an instrument that traditionally works on a system of bellows. It is similar to a harmonium and is used to provide a drone in a practice session or concert of Indian classical music. It is used as an accompaniment to other instruments and notably the flute. Use of the shruti box has widened with the cross-cultural influences of world music and new-age music to provide a drone for many other instruments as well as vocalists.