A Shruti box is a small wooden 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. Shruti boxes provide a rich drone background that supports singing or playing almost any instrument. A shruti box is hand-pumped, so you can produce a slightly pulsating constant chord to support the right rhythm for the style of music you are playing.