Perfect pitch, also called absolute pitch, is the ability to identify a tone's musical qualities without any outside assistance, such as a tuning fork or piano. People with perfect pitch can hear a doorbell ring and recognize the tone as an A above middle C, for example. A musician with it can tune a guitar's strings by sound alone, even detecting very subtle sharps and flats. Very few people have truly perfect pitch, and many of those who do are not musically inclined. Interestingly enough, this ability is much more prevalent among those with autism or diagnosed savants.
Few experts agree on the origins of perfect pitch. Some say the ability to identify tones and frequencies is largely inherent, much like athletic or artistic ability. Some children are able to distinguish different pitches without specific musical training. Those who do receive musical training often consider the ability to be a basic skill, akin to muscle memory for an athlete. When a recognizable tone is played or sung, someone who can hear pitch perfectly does not have to spend time contemplating his or her answer — the note is what it is.
Other experts suggest that perfect pitch, or at least a workable form of it, can be developed over time. Instrumentalists and vocalists who spend hours each day in rehearsal can eventually sense when their instruments are out of tune or their voices are not hitting the right pitches. Someone with innate perfect pitch may become less interested in music, since the rehearsal process is riddled with off-key sounds and other distractions. The ability to hear an ideal pitch can be both a blessing and a curse for musical students.
Some people with this ability can also identify intervals between two notes or all of the notes played together in a chord. Vocalists with perfect pitch are especially favored by composers who want to hear pure intervals. Musicians with it may also be asked to aid in the tuning process, since they can often detect a single out-of-tune instrument or vocalist. Not all successful musicians and composers have perfect pitch. It's a useful skill for performers and conductors, who must use their sense of pitch to make subtle adjustments in tone, but it is not strictly necessary for most creative aspects of the musical arena.