Shruti Box

Ocean Swift Shruti Box VSTi
VSTi 32/64-bit Windows.

Shruti Box VSTi is a small Additive synthesis drone box, a digital rendition of the classic Indian instrument. A very light drone based instrument for quick sonic backgrounds – inspired on the Indian instrument "Shruti Box" – Our version comes with a Tremolo Effect, a Chorus Effect and other controls for Core sound such as "Body" "Damp" and "Shimmer".

A Constant Background Tone
Shruti box VSTi isn't a standard fully equipped synth, nor is it meant to be. This is something different and much more simple, our VSTi follows the same concept as the original instrument – producing constant background drones to be accompanied with other instruments, spoken word, sound effects, additional soundscapes, singing, or whatever comes to mind.

"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. The shruti box is also used in classical singing. In classical singing the shruti box is used to help tune the voice. The 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."
- wikipedia.