Since the Indian Classical music is modal music based on relations between a fixed sound, the tonic and the successive notes. The tonic needs to be heard continuously.The sustained accompaniment of the tonic allows the performer to check his/ her voice to avoid dissonance. This constant tonic is provided by the instrument Taanpura. It has four or sometimes 5/6 strings . The drone is accomplished (explained for a four string taanpura) by playing

   and    (If a particular raag does not include Pancham but has Madhyam eg. Raag Marwa or Malkauns)

Some times it is set to

   or    if the raag has prominence of Dhaivat or Nishad.