In general, the altissimo register of a wind instrument begins one octave above the highest available note in the concert register. For example, the clarinet's altissimo register begins at written G6 (concert A6). Altissimo notes on some instruments are produced by overblowing, while on others they require specific alternate fingerings and embouchure adjustments. Some instruments, like the clarinet and bassoon, have well-established altissimo registers with many notes and fingerings that are commonly played, while others, like the oboe and flute, have more limited altissimo ranges and require more specialised techniques to play.
The altissimo register can be identified by its distinct, piercing sound and is often used for expressive or technical passages in advanced wind playing. It takes significant practice, control, and mastery of the instrument to play altissimo notes well, and is considered to be a mark of advanced technique and musicianship.