Sound is produced on the flute by blowing: the flutist blows through the mouth hole (embouchure hole) and the stream of air that makes contact with the edge is cyclically directed outward and inward. This cyclically vibrating air stream is the sound generator and excites cyclic vibrations of the air column inside the flute’s cylindrical tube. The flutist uses tone holes and keys to shorten the vibrating air column, thus producing an increase in pitch. The sound is projected through the open lower end and the open keys.
It is the flutist’s lips that play the most important role; attack on the flute is highly individual. The shape of the lips, the position of the upper lip in relation to the lower lip, angle of the embouchure etc. are all decisive factors in intonation. There are so many flutists, so many different embouchures and consequently so many different means of expression.
Blowing strongly results in a higher pitch than blowing softly; this is true of all flutes. The flutist compensates for these differences by means of the embouchure.
It is primarily the keywork that is used for sound production, whereas the technique of overblowing, so important on brass instruments, plays only a subordinate role on the flute. This means that flutists mainly use naturals 1 and 2 and only rarely naturals 3 and 4.
With the aid of the keys the notes from B3–D5 are played starting from the fundamental (1st natural). The footjoint is detachable; the C footjoint is standard and contains the tone holes for the low notes from Eb4 to C4. By replacing it with a B footjoint B3 becomes playable as well (although the higher notes do not respond so well on this footjoint).
By overblowing to the 2nd natural (octave) the range Eb5–D6 becomes available:
The high notes are generally produced by means of special fingerings rather than by overblowing. Exceptions are made in difficult passages, however, where it is not unusual for the notes D6 through A6 to be produced by overblowing to the 3rd natural (twelfth).
The harmonics which are less often called for can be played by overblowing to the 4th natural (2 octaves above the fundamental). These notes (from B5–A6) sound almost exactly the same as the regular piano or pianissimo notes.
D7 requires a forced attack, while the notes above it as far as F7 can only be produced with extreme force and are therefore not called for in orchestral literature.