Shruti box, tanpura, tuning drone: one job, three instruments
A tanpura is the traditional source of the drone in Hindustani and Carnatic music: four long strings, tuned to Pa, Sa, Sa and the lower Sa (or Ma or Ni in place of Pa for ragas that avoid the fifth), plucked one after another in an unbroken cycle. The curved bridge with its threads, the jivari, is what makes the sound bloom with overtones, so the drone is never just a note but a whole shimmering field of harmonics around Sa.
A shruti box is the simpler relative: a bellows and a set of reeds, essentially a harmonium with the keyboard taken away, sustaining a chosen Sa and usually Pa, sometimes the upper Sa as well. It does not cycle or bloom the way a tanpura does; it simply holds. That steadiness, plus a price and a size a student can manage, is why it became the everyday practice drone, and why electronic shruti boxes and tanpura apps followed.
A Western tuning drone is the same idea arrived at from the other direction: a sustained reference note that string, wind and voice students play against to train intonation by ear. Whatever the name, the job is identical. Hold an exact pitch continuously, so that the musician learns to hear every note in relation to it. The drone on this page is a tuning drone set up to behave as a shruti box: a warm, reedy voice on the Sa you choose, with the upper Sa blended in.
Choosing your Sa
Sa is not a fixed frequency. Unlike Western concert pitch, where A is 440 Hz for everyone, each musician chooses the Sa that suits their voice or their instrument, and the whole raga moves with it. Harmonium players name the choice by key colour and position: safed (white) and kali (black), counted from C, so safed 1 is C, kali 1 is C sharp, safed 2 is D, and so on up to kali 4 (G sharp) and safed 6 (A).
| Voice or instrument | Common Sa | On this drone |
|---|---|---|
| Male vocal | Safed 1, kali 1 or safed 2 (C, C sharp, D) | C, C# or D, octave 3 |
| Female vocal | Safed 5, kali 4 or safed 6 (G, G sharp, A) | G, G# or A, octave 3 |
| Sitar | Kali 1 or safed 2 | C# or D, octave 3 |
| Sarod | Safed 1 or kali 1 | C or C#, octave 3 |
| Bansuri | The flute's own Sa (an E bansuri has Sa on E) | The named note, octave 3 or 4 |
| Violin (Carnatic) | Usually matched to the vocalist | Whatever the singer's Sa is |
If you are choosing for the first time, sing the lowest phrase of a raga you know and the highest, and find the Sa on which both are comfortable. A Sa that is too high strains the top; too low, the lower octave disappears. Once chosen, keep it: a settled Sa is what lets the ear build its map of the swaras.
How to practise with the drone
Start with Sa itself. Sing or play Sa against the drone and listen for the moment the two sounds fuse into one. If you hear a slow pulsing, a wavering in the loudness, you are slightly off; slide until it stops. That pulsing is called beating, and hearing it stop is the entire skill.
Then Pa, then the rest. Hold Pa against the drone and listen for the same fusion, a pure fifth locking in. Then Ma, then each swara of the raga, sustaining each one until it sits. Every note has a place where it stops beating against Sa; that place is the shruti.
Slow alankars over the drone. Sa Re Ga Ma, Re Ga Ma Pa, and so on, slowly, letting each note settle before moving. Speed comes later and comes easily once the ear knows where each note lives.
Keep the drone on for the whole session. Unlike a metronome, which you may switch off for free playing, the drone should sound throughout riyaz. Its whole value is that Sa is always there to return to.
Sa and Pa together
A tanpura's first string is Pa, and a shruti box nearly always sounds Pa alongside Sa. On a real tanpura the Pa string is tuned by ear until it stops beating against Sa, which puts it at a pure 3:2 fifth, a shade wider than the fifth on a keyboard or harmonium. That pure fifth is why a tanpura sounds so settled and a harmonium drone slightly restless. In the Metro Gnome app, the drone's Fifth blend sounds Sa and Pa at exactly that 3:2 ratio, alongside Reed and String voices that carry more harmonics than the two free voices here. The browser drone offers Sa alone or Sa with the upper Sa, which is the tanpura's second, third and fourth strings without the first.
Reference pitch, if you play with a harmonium
Because Sa is chosen freely, the drone's A4 reference only matters when you have to match an instrument that cannot retune. Most harmoniums are built to A4 = 440 Hz, some slightly higher. The full tuning drone has an A4 control from 415 to 466 Hz; set it to whatever your harmonium is at and every Sa on the keyboard moves with it. For voice, sitar, sarod or bansuri alone, leave it at 440 and choose Sa by ear.
Questions about shruti boxes and Sa
What is a shruti box?
What is the difference between a shruti box and a tanpura?
What is Sa, and what note should mine be?
Can a tuning drone replace a shruti box?
Can I get Sa and Pa together, like a tanpura's Pa string?
Is this online shruti box free?
Sa and Pa together, on your phone, next to a tuner.
Metro Gnome's drone holds Sa on any note from C2 to B5, adds Pa as a pure 3:2 fifth with the Fifth blend, and sits in the Tuner tab so you can check a swara against the needle the moment you stop the drone. Free on Android, no account, no subscription.
Get it Free on Google PlayUse this on your own site
The drone embeds on any website with one line of HTML, free, with no sign up and no API key, and you can pre-set the Sa in the link (for example ?note=Cs&octave=3&blend=octave). Music schools and teachers are welcome to put it on a lesson page for students. Get the embed code.