What Is a Drone? A Sustained Note That Everything Else Is Heard Against

A sustained note fixes a reference pitch that never moves, so every note of the melody is heard in relation to it rather than in relation to what came before. That makes intervals audible as qualities rather than as steps, since a note sounding against a constant reference has a definite character that changes as the melody moves, and traditions built around this develop a vocabulary for those characters. It also removes the need for harmony in the Western sense, since the vertical relationship is supplied continuously by one note and does not have to be constructed from chords. And it produces acoustic effects, since the overtones of the drone interact with the melody notes, reinforcing some and beating against others, which adds a shimmer that a melody alone does not have.

Producing a continuous note requires specific design and several solutions exist:

• •Bagpipes, where a bag holds air so the player can breathe while separate pipes sound continuously
• •The hurdy gurdy, where a rotating wheel bows several strings at once, some stopped for melody and others left open
• •The tanpura in Indian music, an instrument with no melodic function whose entire purpose is the reference
• •Drone strings on instruments including the sitar, the sarangi and several European folk fiddles
• •Organ stops and harmoniums, where a key can simply be held
• •The human voice in traditions where one group holds a note while another sings above it

The distribution is extremely wide and largely independent. Indian classical music is built on it entirely, with the reference sounding throughout a performance and the entire theory of melodic modes defined relative to it. Scottish, Irish, Breton, Galician, Balkan, Bulgarian and numerous other European traditions use drone instruments or drone singing. Central Asian traditions include overtone singing, where a single performer produces a drone and a melody simultaneously. Australian, African and Middle Eastern traditions include comparable practices. Western art music largely abandoned it as harmony developed, retaining it as an occasional effect, and returned to it in the twentieth century through minimalist composition and through the influence of the traditions that had kept it. The near-universality suggests it answers something basic about how melody is heard.

Beyond its harmonic function the drone produces a specific acoustic experience that traditions exploit deliberately. A sustained note contains a whole series of overtones, and those are audible as a shimmer that the ear can pick out with attention, which is the basis of overtone singing and of the way a tanpura is tuned and plucked to maximise the effect. Beating occurs where a melody note is close to but not exactly at a simple ratio with the drone, producing a pulsing that a player can hear and use to adjust pitch precisely, which is why drone traditions frequently achieve intonation far more exact than notation-based ones. The continuous sound also removes silence, so a performance has no gaps and the listener is held inside it, which several traditions describe explicitly as part of the intended effect.

A constant reference has a substantial effect on what intervals sound right, which is why drone traditions and keyboard traditions tune differently. Against a fixed note, intervals corresponding to simple whole-number frequency ratios sound smooth and pure, since their overtones align, while intervals slightly away from those ratios produce audible beating. A tradition built around a drone therefore tends towards those pure intervals, and performers on instruments with flexible pitch adjust continuously to achieve them. Keyboard instruments cannot, since a fixed tuning must serve every key, and the compromise adopted in Western practice spreads small errors across all intervals so that none is pure and none is unbearable. That compromise is nearly inaudible without a drone and conspicuous with one, which is why music from drone traditions sounds out of tune on a piano and why the piano sounds out of tune against a tanpura.

A constant note makes every melody note heard against a fixed reference, so intervals register as qualities rather than steps and harmony need not be constructed from chords. Bags, wheels, dedicated instruments and held voices all solve the problem of sustaining one. Against a drone the pure whole-number intervals sound right, which is why keyboard tuning conspicuously does not.