The whistle register, an extraordinary vocal capability, typically originates above the soprano's "high C" (C6, at 1047 Hz) and extends up to two Ds higher (D7, 2349 Hz) in most singers. However, individual variation exists, with some exceptional female voices capable of reaching far beyond these frequencies. For instance, opera singers can occasionally hit notes as high as the "high" F above "C", without entering the whistle register. Notably, Brazilian singer Georgia Brown possessed an extraordinary range, reaching a G10 (25,087 Hz), demonstrating the extraordinary potential of some vocalists.
The whistle register's physiological intricacies remain largely uncharted territory. Its production involves a unique process that is challenging to visualize, as the epiglottis closes over the larynx, shrinking the resonating chamber. When producing pitches in this register, vibrations predominantly occur in the anterior part of the vocal folds, which, due to a shorter length, facilitate the creation of high-pitched tones.
When the lateral muscles are active but the transversus remains inactive, a distinctive triangular opening forms between the arytenoids. The vocal processes touch each other, but the posterior parts do not meet at the apex. However, this pattern can deviate if the vocal folds are not stretched. In such cases, the stretching of vocal ligaments moves the vocal processes apart, altering the typical vocal mechanism.
海豚音（Dolphin vocal sound or Whistle register ），顾名思义，就是指一些像海豚一样发出的在人类听频范围外的高音调超声波。当然，人是无法发出超声波的。所以，海豚音用来泛指人类发出的极高的音调。海豚音也是至今为止人类发声频率的上限。海豚音这个词是非音乐人士创造出来的新词，而非声乐上的名词。