Perfect pitch, also called absolute pitch, is the ability of a person to identify or re-create a given pitch without the use of a reference pitch. It can be manifested in any of several ways, including by humming or singing a requested note, naming a sounded note, or reproducing on an instrument a sounded or named note without 'hunting.'
Perfect pitch is very rare, perhaps far less than one percent of the population. However, it is apparently more common among music students, people who speak tonal languages, such as Chinese and Vietnamese, people who are blind from birth, and people with Asperger's syndrome. Much more common is relative pitch, which is the ability to identify the pitch when a reference pitch is provided. Some animals, such as some bat and bird species, are also said to have perfect pitch, including for facilitating identification of mates.
It is not known whether perfect pitch in humans is innate or acquired in early childhood. However, it is clear that it is not the result of a keener sense of hearing but rather is a process that takes place in the brain.