This last definition, which applies not only to singers but also to players of instruments who rely on their own skill to determine the precise pitch of the notes played (wind instruments, fretless string instruments like violin or viola, etc.), is an essential professional skill to be able to play with others. As an example think of the different concert pitch used by orchestras playing music from different styles (a baroque orchestra with original instruments might decide to use a much lower pitch). A soloist singer trying to sing in the perfect pitch would sound constantly "out of tune".
Unlike absolute pitch (sometimes called "perfect pitch"), relative pitch is quite common among musicians, especially musicians who are used to "playing by ear", and a precise relative pitch is a constant characteristic among good musicians. Also unlike perfect pitch, relative pitch is common among non-musicians and can be developed through ear training.
Some music teachers teach their students relative pitch by having them associate each possible interval with the first two notes of a popular song. (See ear training.) Another method of developing relative pitch is playing melodies by ear on a musical instrument, especially one which, unlike a piano or other fingered instrument, requires a specific manual adjustment for each particular tone. Indian musicians learn relative pitch by singing intervals over a drone, which is also described by W. A. Mathieu using western just intonation terminology. Many western ear training classes use solfège to teach students relative pitch, while others use numerical sight-singing.
Compound intervals (intervals greater than an octave) can be more difficult to detect than simple intervals (intervals less than an octave).
Interval recognition may allow musicians to identify complex chord types, or to accurately tune an instrument with respect to a given reference tone, even if the tone is not in concert pitch.
Relative pitch has not been known to develop into absolute or perfect pitch. Most North American universities develop relative pitch in their ear training courses. This can pose difficulties for students whose musicianship is more dependent on perfect pitch, although absolute and relative skills are not mutually exclusive.