register

The whistle register (also called the flute register or flageolet register) is the highest register of the human voice, lying above the modal register and falsetto register. This register has a specific physiological production that is different from the other registers and is so called because the timbre of the notes that are produced from this register is similar to that of a whistle.
In some sopranos, the modal register vocal production (the high head voice part) may extend into what is usually thought to be the whistle register.

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