Relative pitch

Relative pitch is the ability of a person to identify or re-create a given musical note by comparing it to a reference note and identifying the interval between those two notes. Relative pitch implies some or all of the following abilities:
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 skill for musicians in order to play successfully with others. An example, is the different concert pitches used by orchestras playing music from different styles (a baroque orchestra using period instruments might decide to use a higher-tuned pitch).
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. Unlike perfect pitch, relative pitch can be developed through ear training. Computer-aided ear training is becoming a popular tool for musicians and music students, and various software is available for improving relative pitch.
Some music teachers teach their students relative pitch by having them associate each possible interval with the first two notes of a popular song. 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 is used to identify chords, and can be applied to accurately tune an instrument with respect to a given reference tone, even if the tone is not in concert pitch.