Absolute pitch (AP), widely referred to as perfect pitch, is an auditory phenomenon characterized by the ability of a person to identify or re-create a given musical note without the benefit of a reference tone.
AP can be demonstrated via linguistic labeling ("naming" a note), auditory imagery, or sensorimotor responses. For example, an AP possessor can accurately reproduce a heard tone on their musical instrument without "hunting" for the correct pitch.
Generally, absolute pitch implies some or all of the following abilities, achieved without a reference tone:
- Identify by name individual pitches (e.g. A, B, C♯) played on various instruments.
- Name the key of a given piece of tonal music.
- Reproduce a piece of tonal music in the correct key days after hearing it.
- Identify and name all the tones of a given chord or other tonal mass.
- Accurately sing a named pitch.
- Name the pitches of common everyday sounds such as car horns and alarms.
People may have absolute pitch along with the ability of relative pitch, and relative and absolute pitch work together in actual musical listening and practice, but strategies in using each skill vary. Those with absolute pitch may train their relative pitch, but there are no reported cases of an adult obtaining absolute pitch ability through musical training; adults who possess relative pitch, but who do not already have absolute pitch, can learn "pseudo-absolute pitch", and become able to identify notes in a way that superficially resembles absolute pitch. Moreover, training pseudo-absolute pitch requires considerable motivation, time, and effort, and learning is not retained without constant practice and reinforcement.
Scientific studies 
History of study and terminologies 
Scientific study of absolute pitch appears to have commenced in the 19th century, focusing on the phenomenon of musical pitch and methods of measuring it. While the term absolute pitch, or absolute ear, was in use by the late 19th century by both British and German researchers, its application was not universal; other terms such as musical ear, absolute tone consciousness, or positive pitch were also used to refer to the ability. The skill is not exclusively musical, or limited to human perception; absolute pitch has been demonstrated in animals such as bats, wolves, gerbils, and birds, for whom specific pitches facilitate identification of mates or meals.
Difference in cognition, not elementary sensation 
Physically and functionally, the auditory system of an absolute listener does not appear to be different from a non-absolute listener. Rather, "it reflects a particular ability to analyze frequency information, presumably involving high-level cortical processing." Absolute pitch is an act of cognition, needing memory of the frequency, a label for the frequency (such as "B-flat"), and exposure to the range of sound encompassed by that categorical label. Absolute pitch may be directly analogous to recognizing colors, phonemes (speech sounds) or other categorical perception of sensory stimuli. Just as most people have learned to recognize and name the color blue by the frequencies of the electromagnetic radiation that is perceived as light, it is possible that those who have been exposed to musical notes together with their names early in life will be more likely to identify, for example, the note C. Absolute pitch may also be related to certain genes, possibly an autosomal dominant genetic trait, though it "might be nothing more than a general human capacity whose expression is strongly biased by the level and type of exposure to music that people experience in a given culture."
Influence by music experience 
Absolute pitch sense appears to be influenced by cultural exposure to music, especially in the familiarization of the equal-tempered C-major scale. Most of the absolute listeners that were tested in this respect identified the C-major tones more reliably and, except for B, more quickly than the five "black key" tones, which corresponds to the higher prevalence of these tones in ordinary musical experience. One study of Dutch non-musicians also demonstrated a bias toward using C-major tones in ordinary speech, especially on syllables related to emphasis.
Absolute pitch is more common among speakers of tonal languages such as most dialects of Chinese or Vietnamese, which often depend on pitch variation as the means of distinguishing words that otherwise sound the same; e.g. Mandarin with four possible pitch variations, Cantonese with six to nine (depending on dialect), Minnan with seven or eight (depending on dialect), and Vietnamese with six. Speakers of Sino-Tibetan languages have been reported to speak a word in the same absolute pitch (within a quarter-tone) on different days; it has therefore been suggested that absolute pitch may be acquired by infants when they learn to speak a tonal language (and possibly also by infants when they learn to speak a pitch-accent language). However, the brains of tonal-language speakers do not naturally process musical sound as language; perhaps such speakers are more likely to acquire absolute pitch for musical tones when they later receive musical training. Many native speakers of a tone language, even those with little musical training, are observed to sing a given song consistently with regard to pitch. Among music students of East Asian ethnic heritage, those who speak a tone language very fluently have a much higher prevalence of absolute pitch than those who do not speak a tone language.
It is possible that African level-tone languages—such as Yoruba, with three pitch levels, and Mambila, with four—may be better suited to study the role of absolute pitch in speech than the pitch and contour tone languages of East Asia.
Speakers of European languages have been found to make subconscious use of an absolute pitch memory when speaking.
Absolute pitch is the ability to perceive pitch class and to mentally categorize sounds according to perceived pitch class. Pitch class is a tonal quality which recurs among tones which share the relationship of an octave. While the boundaries of musical pitch categories vary among human cultures, the recognition of octave relationships is a natural characteristic of the mammalian auditory system. Accordingly, absolute pitch is not the ability to estimate a pitch value from the dimension of pitch evoking frequency (30–5000 Hz), but to identify a pitch class category within the dimension of pitch class (e.g., C-C♯-D ... B-C).
An absolute listener's sense of hearing is typically no keener than that of a non-absolute ("normal") listener. Absolute pitch does not depend upon a refined ability to perceive and discriminate gradations of sound frequencies, but upon detecting and categorizing a subjective perceptual quality typically referred to as "chroma". The two tasks— of identification (recognizing and naming a pitch) and discrimination (detecting changes or differences in rate of vibration)— are accomplished with different brain mechanisms.
Special populations 
The prevalence of absolute pitch is higher among those who are blind from birth as a result of optic nerve hypoplasia.
Absolute pitch is considerably more common among those whose early childhood was spent in East Asia. This might seem to be a genetic difference; but people of East Asian ancestry who are reared in North America are significantly less likely to develop absolute pitch than those raised in East Asia, so the difference is more probably explained by experience. The language that is spoken may be an important factor; many East Asians speak tonal languages such as Mandarin and Cantonese, while others (such as those in Japan and certain provinces of Korea) speak pitch-accent languages, and the prevalence of absolute pitch may be partly explained by exposure to pitches together with meaningful musical labels very early in life.
Absolute pitch ability has higher prevalence among those with Williams Syndrome and those with an autism spectrum disorder, with rates as high as 30% claimed, stating that the rate among musicians in general is far lower.[clarification needed]
Nature vs. nurture 
Absolute pitch might be achievable by any human being during a critical period of auditory development, after which period cognitive strategies favor global and relational processing. Proponents of the critical-period theory agree that the presence of absolute pitch ability is dependent on learning, but there is disagreement about whether training causes absolute skills to occur or lack of training causes absolute perception to be overwhelmed and obliterated by relative perception of musical intervals.
There may be a genetic locus for absolute pitch ability, which locus would suggest a genetic basis for its presence or absence. A genetic basis, should it exist, might represent either a predisposition for learning the ability or signal the likelihood of its spontaneous occurrence.
An unequivocal resolution to the ongoing debate would require controlled experiments that are both impractical and unethical. Researchers have been trying to teach absolute pitch ability in laboratory settings for more than a century, and various commercial absolute-pitch training courses have been offered to the public since the early 1900s. However, no adult has ever been documented to have acquired absolute listening ability, because all adults who have been formally tested after AP training have failed to demonstrate "an unqualified level of accuracy... comparable to that of AP possessors".
While very few people have the ability to name a pitch with no external reference, pitch memory can be activated by repeated exposure. People who are not skilled singers will often sing popular songs in the correct key, and can usually recognize when TV themes have been shifted into the wrong key. Members of the Venda culture in South Africa also sing familiar children's songs in the key in which the songs were learned.
This phenomenon is apparently unrelated to musical training. The skill may be associated more closely with vocal production. Violin students learning the Suzuki method are required to memorize each composition in a fixed key and play it from memory on their instrument, but they are not required to sing. When tested, these students did not succeed in singing the memorized Suzuki songs in the correct key.
Possible problems 
Musicians with absolute perception may experience difficulties which do not exist for other musicians. Because absolute listeners are capable of recognizing that a musical composition has been transposed from its original key, or that a pitch is being produced at a nonstandard frequency (either sharp or flat), a musician with absolute pitch may become distressed upon perceiving tones they believe to be "wrong" or hearing a piece of music "in the wrong key." This can especially apply to Baroque music that is recorded in Baroque tuning (usually a half step down from standard concert pitch). An absolute listener may also use absolute strategies for tasks which are more efficiently accomplished with relative strategies, such as transposition or producing harmony for tones whose frequencies do not match standard equal temperament. It is also possible for some musicians to have skewed absolute pitch, where all notes are slightly flat or slightly sharp. When playing in groups with other musicians, this may lead to playing in a tonality that is slightly different from the rest of the group.
Correlation with musical talent 
Absolute pitch is not a prerequisite for skilled musical performance or composition. Studies have shown both positive and negative impacts of AP on musically skilled tasks: musicians with absolute pitch tended to perform better on transcription when compared to musicians with similar onset and duration of musical training, but musicians with absolute pitch also showed poorer abilities at recognizing musical intervals (for some reference notes other than C). No test yet exists for comprehensively and objectively measuring the influence of absolute pitch ability on musicianship.
Owing to uncertainty in the historical record, it is often impossible to determine whether notable composers and musicians had absolute pitch. Since absolute pitch is rare in European musical culture, claims that any particular musician possessed it are difficult to evaluate. Among composers of the Baroque and Classical eras, evidence is available only for Mozart, who is documented to have demonstrated the ability at age 3. Experts have only surmised that Beethoven had it, as indicated from some excerpts from his letters. By the 19th century, it became more common for the presence of absolute pitch to be recorded, identifying the ability to be present in musicians such as Camille Saint-Saëns and John Philip Sousa.
Relative pitch 
Many musicians have quite good relative pitch, a skill which can be learned through ear training. With practice, it is possible to listen to a single known pitch once (from a pitch pipe or a tuning fork) and then have stable, reliable pitch identification by comparing the notes heard to the stored memory of the tonic pitch. Unlike absolute pitch, this skill is dependent on a recently perceived tonal center.
See also 
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- Online absolute pitch test together with answers, from Diana Deutsch’s laboratory at the University of California, San Diego
- Online absolute pitch survey and test with information about the absolute pitch study conducted at the University of California-San Francisco
- Comprehensive historical bibliography of absolute pitch research, 1876–present
- Another bibliography of absolute pitch, with +300 papers