Tin whistle all the holes closed, the whistle generates its lowest note, the tonic of a major scale. Successively opening holes from the bottom upward produces the rest of the notes of the scale in sequence: with the lowest hole open it generates the second, with the lowest two holes open, it produces the third and so on. With all six holes open, it produces the seventh. As with a number of woodwind instruments, the tin whistle's second and higher registers are achieved by increasing the air velocity into the ducted flue windway. On a transverse flute this is generally done by
Tin whistle perfect fourth apart and the natural minor key and Dorian mode a major second above the lowest note. The whistle is identified by its lowest note, which is the tonic of the lower of two major keys whose tonics are a perfect fourth apart that the whistle most easily plays in. Note that this method of determining the key of the instrument is different from the method used to determine the key of a chromatic instrument, which is based on the relationship between notes on a score and sounded pitch. Whistles are available in a wide variety of different keys.