I would like to share a little about the instruments that feature within the soundscape of Indian classical music and Dhrupad in particular. For that there is only one place to start!
Probably the single most characterestic feature of Indian classical music is the ubiquitous sound of the Tanpura, an impressive instrument to behold, made from a giant gourd at the base and either teak or Indian mahogany for the long neck. It has four or five strings typically, two of which are tuned to the middle Sā or tonic pitch, one of which is tuned to the lower octave Sā, and the last of which is tuned to either Pa, the dominant or 5th of the scale, or Nī, the leading note or 7th of the scale. These are plucked in sequence, repetitively for the duration of the music performance which creates the characteristic drone sound upon which the music unfolds. In itself, it has no melody or variety but it provides a vital sonic backdrop, a pitch reference and also a source of inspiration to the musician.
Just listening to the sound of the Tanpura can be a meditative and hypnotic experience to the lay listener but to the trained musician it has the power to provoke the unfolding of a Rāga in their mind.
According to Indian classical treatises there are two types of sound: Āhat (struck) and Anāhat (unstruck) Nāda (sound current). The former consists of any sound which is created by friction between objects and the latter corresponds to any sound which comes about without the direct use of such friction. The universe itself and all matter exists from vibrating atoms, it’s just that the frequencies of most objects are beyond human audible range. The universe is thus made up of Anāhat Nāda – an extension of the so called ‘big bang’. An overt example of how sound and matter are inseparable is in the way that an opera singer can smash a glass window by singing at a high frequency pitch.
Anyway, I don’t wish to digress too far into the nature of the universe! When perfectly tuned the playing of the tanpura emits both types of sound; Āhat Nāda in the form of the tones of the four plucked strings and Anāhat Nāda in the form of the myriad overtones which come about due to their harmonic relation to the plucked tones. The resulting sound is so rich that it beckons forth the music.
In Dhrupad there is typically no melodic accompaniment other than the sound of the Tanpura thus its presence and correct tuning are of vital importance. Here’s a clip of my very talented gurū bhāī, Sagar Morankar, expertly tuning the Tanpura and demonstrating its sound.