Shruti is the pitch (base note reference) of the music. The artist must perform in sync with shruti. The knowledge of Shruti or Shruti Jnana is utmost important. Different artists have different comfortable Shruti. Shruti is played traditionally using Tanpura, or Harmonium. But modern day gadgets have made it possible to have an electronic Shruti box, which mimics the drone. This box is very portable compared to Tanpura or Harmonium. In the current period, it is so easy to play the Shruti through Smartphone apps.
Picture of Tanpura or Tamburi