Shruti box

It is similar to a harmonium and is used to provide a drone in a practice session or concert of Indian classical music.

Before the arrival of the harmonium in the Indian subcontinent, musicians used either a tambura or a specific pitch reference instrument, such as the nadaswaram, to produce the drone.

[citation needed] Later, a keyless version of the harmonium was invented for the specific purpose of producing the drone sound.

[citation needed] The shruti box is enjoying a renaissance in the West among traditional and contemporary musicians, who are using it for a range of different styles.

More recently Scottish folk artists Karine Polwart and Julie Fowlis used the instrument on some of their songs.