Bansuri (Flute)

The lips direct a narrow air jet across the blowing hole onto its far edge. The jet works in step with resonances of the air column inside the bamboo, and together they sustain the vibration you hear as sound. The tube is closed at the end nearest the blowing hole. A concert bansuri in the Horniman Museum, London (2007.468), seals that end with a cork stopper.

Rolling the flute so that the lip covers more of the blowing hole lowers a note a little. Players start and separate notes with tonguing, a light stroke of the tongue; single, double, triple and flutter tonguing are all possible. Vibrato comes from rocking a finger over an open hole or from the breath. Carl Clements, who analysed the recordings of Pannalal Ghosh, finds that Hariprasad Chaurasia tongues more than Ghosh did, and suggests he does so to echo plucked strings. Clements links the flute's closeness to the voice to two features: notes that sustain for as long as the breath lasts, and glides as fluent as a singer's.

The bansuri has no keys. The fingers cover, uncover or part-cover the open holes, and the pattern of covered holes decides which note the air column sounds. Sliding a finger on or off a hole by degrees produces meend, a continuous glide from one pitch to another, and the same partial covering gives the microtonal ornaments of raga phrasing. The Natyasastra, an early treatise that its translator Manomohan Ghosh dates to about 200 CE, gives flute notes made from open holes, half-open holes and holes under a shaken finger.

One composers' guide names each flute by its pipe note, the note sounded with every hole closed, and places Sa, the tonic, with the three upper holes closed, a fourth above that note. The pitch of Sa depends on the size of the flute. Makers tune single notes by enlarging or reducing a hole, and the scale does not follow equal temperament, the piano tuning that splits the octave into twelve equal steps. Fingerings in the third octave vary with the bamboo and with how the player blows.

A higher note needs the air jet to reach the edge sooner, so the player blows a faster, shorter jet. The register break is the point where the flute moves up to the next overtone to sound the higher octave. A glide cannot cross the break without a jump in the line.

Length sets the overall pitch: longer flutes sound lower. The Horniman concert flute measures 650 mm, about 26 inches, and a composers' guide lists sizes from about 14 to 30 inches, with the longest rare and hard to play. A finished flute cannot be retuned by shortening it, since the holes would then sit in the wrong places. The playable range depends on the flute and the player. Published figures run from about two octaves and a third to three octaves or more for an expert, with the top notes the hardest to control and keep in tune.