The following text is taken from the book "Classical Musical Instruments" by Suneera Kasliwal, Delhi 2001.
Bansuri
Bansuri is a very sensitive instrument; almost all the delicate graces, curves, embellishments and shades of classical music can be performed to perfection upon it. The highest order of music can be played on this instrument, and its resonance in mandra saptak (lower octave) leaves a rare charm in the minds of its listeners. Being a portable instrument, it can be carried easily from place to place and climatic changes have very little or no effect on the seasoned bamboo.
The flute is a simple bamboo tube of uniform bore. The tube must be closed at one end. The closure may be natural, that is by the node of the stem, or, if there is no natural closure, one end may be plugged with a cork or stopper. The bamboo chosen to make the flute must be selected very carefully. It should be neither too old nor too young a plant, of medium thickness, and the stem should be clean and smooth, free from cracks, bumps, holes or other damages. Once selected the bamboo tube is best dried in the shade for approximately one year. It is then ready to be converted into a flute, to have holes of an appropriate-size and number pierced into it. The best bamboo comes from the northeast region, preferably from Assam or Tripura.
The length of the flute is normally between two-and-a- half feet to less than three feet, depending upon the thickness of the wall and density of the bamboo.
The North Indian flute normally has six finger holes and one blowing hole, but some artists make one extra hole, thus bringing the total number to eight. Panna Babu had an extra hole for teevra ma in lower octave. In the ancient frescoes and temple sculptures, flutes are depicted as having only six holes. Six fingers and six holes, as it is still by and large a rule in the music of the North. Artists using a bamboo key use their little finger to press the key as an exception. However, some purists feel that the use of the key is an impediment to playing andolita swaras, delicate sruties and the more subtle nuances of Indian music. The fingers have to be in direct contact with the finger holes to produce all the delicacies and intricacies of the various ragas. Therefore, in Indian flutes, the keys should not be used in the manner the Western flautists do.
While playing, the flute is placed horizontally, a little tilted towards the ground. The artist mostly sits cross-legged on the floor, keeps his trunk straight and head high. This helps him to fill in his lungs with more air that spurs him to breathe better, blow better and provide a continuity and consistency to his blowing for hours together. The player has to figure out his own angle from where the instrument is best suited to him to give him the best tone. By controlling the breath, different sound modulations are achieved. With the help of the tongue and throat the air is stroked and special mnemonics such as 'ta' and *ka' are produced.
Along with the main flute of D sharp, artists normally use a lower octave flute called the bass flute to delineate the ragas in mandra saptak during the alap. Artist also keep a small flute to play lighter number, like bhatyali or chaiti or other folk tunes generally to end the programme. The main D sharp North Indian flutes could produce three octaves accurately, two-and-a-half with ease and half octave in upper octave. With an open blowing (without closing the holes) the player gets teevra madhyam, and after closing all the holes again the swar emitted is teevra madhyam. The rest of the swaras are played by closing the holes one by one. For komal and teevra swaras (semi-tones) and for different octaves, either the player has to partially close the holes or control his breath.