Cold-Hall Pitch Drift on a Bass Bansuri
At a district +2 vocational practical, a bansuri candidate plays a 12-minute solo beginning at 9:00 a.m. in an air-conditioned hall held at 20 °C, with stage lights adding heat after the first five minutes. Her instrument is a bass bansuri with Sa at approximately C#4; the electronic tanpura is set to C# and can be shifted only by whole semitones. During an eight-minute warm-up a tuner reads Sa as −10 cents in mandra saptak, 0 in madhya and +35 in taar; the reading climbs further when she tightens her embouchure for jhala. She has no second flute at this pitch, the changeover between candidates is three minutes, and the sound engineer proposes clipping a mic 10 cm above the blow-hole. Her programme is Raag Bhairav: vilambit gat in teental, drut gat, then jhala, with the designed climax two octaves above Sa. Judges award separate marks for sur and tone.
1. Explain why the three saptaks give different tuner readings, and decide what the tanpura reference should finally be. Justify the decision rather than just stating it.
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Two mechanisms are at work. First, temperature: the speed of sound in air rises by roughly 0.17% per °C, about 3 cents per °C, so a bamboo tube that starts at 20 °C and is warmed to near 30 °C by breath and body heat sharpens by roughly 25–30 cents - which matches the +35 cents in taar, where she also blows harder. Second, the air-jet: a tighter, faster jet for the upper octave raises pitch further, while the loose, slow jet of mandra flattens it.
A bansuri has no tuning device, so the instrument cannot be corrected; the reference must move instead. She should warm the flute fully (five to eight minutes of long tones across all three saptaks), read the stable madhya-saptak Sa, and have the tanpura set to that pitch - not to a textbook C#. If the tanpura only shifts in semitones, she should choose the semitone nearest her warmed Sa and accept a small constant offset, because internal consistency between flute and drone matters more than absolute pitch. Retuning or chasing the tuner mid-performance would be the worst option: it would make the drift audible as a slide.
2. Set out what she should do in the three-minute changeover and in the first two minutes of playing, and what she should tell the sound engineer.
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Changeover plan: keep the flute under her arm or in a cloth so it does not cool; play soft long tones immediately - mandra, madhya, taar - so the instrument reaches thermal equilibrium before the tanpura is set, and ask the tanpura operator to set the pitch only after that warm-up, not before it. In the first two minutes of the actual item, the vilambit gat's alaap should stay in madhya saptak: this both settles the air column and lets the audience hear a stable Sa before any register jump.
Mic advice: 10 cm above the blow-hole is too close. It will pick up breath noise and jet turbulence, and proximity effect will thicken the low register until the engineer boosts bass and the flute sounds stuffy. Ask for 25–30 cm, slightly off-axis and above the blow-hole, with a short sound check at the tanpura's actual level. Also ask him not to ride gain during the jhala; a compressor lifting the top octave will exaggerate exactly the sharpness she is trying to hide.
3. The jhala in taar saptak is the main cause of the drift. Propose a musical solution that keeps a climax but controls pitch.
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Change the shape of the climax rather than removing it. Options, in order of preference:
- Place the jhala's peak in the upper madhya and lower taar (around the taar Pa), reserving the top Sa for single accents on sam rather than continuous playing.
- Shorten the continuous taar section to four to six avartans and end with a tihai that descends into madhya, so the last thing the judges hear is stable.
- Use faster, narrower air with a smaller aperture instead of more pressure; pressure is what pushes pitch up.
- Keep a corrective: rolling the flute slightly inward covers a little more of the blow-hole and flattens the note. It darkens tone, so use it on sustained taar notes only, not in fast passages.
- Rehearse the whole item against a drone, checking pitch at every sam by ear, not with a tuner - the tuner encourages constant small adjustments, which is itself a fault.