Perfect pitch

Absolute pitch, often called perfect pitch, is the ability to identify a note by ear without a reference tone. Some adults can develop this through training.

Ear training

Ear training is the practice through which musicians learn to identify pitches, intervals, melodies, chords, and rhythms by ear.

The notes

In Western music, the chromatic scale is the set of twelve pitches within an octave. The interval between any two adjacent notes is a semitone.

Tap a note to hear it (sine wave, octave 4).

All twelve semitones are equal in size. The frequency ratio between any two adjacent notes is the twelfth root of two.

The note A above middle C is tuned to 440 Hz, the standard reference pitch most instruments are calibrated to.

A pitch class is the set of all pitches a whole number of octaves apart. Every C on the keyboard belongs to pitch class C.

Drawn from Wikipedia: Absolute pitch, Ear training, Chromatic scale, A440, Equal temperament, Pitch class.