Concert pitch

Concert pitch is the pitch reference to which a group of musical instruments are tuned for a performance. Concert pitch may vary from ensemble to ensemble, and has varied widely over time. The ISO defines international standard pitch as A440, setting 440 Hz as the frequency of the A above middle C. Frequencies of other notes are defined relative to this pitch.

The written pitches for transposing instruments do not match those of non-transposing instruments. For example, a written C on a B♭ clarinet or trumpet sounds as a non-transposing instrument's B♭. The term "concert pitch" is used to refer to the pitch on a non-transposing instrument, to distinguish it from the transposing instrument's written note. The clarinet or trumpet's written C is thus referred to as "concert B♭".^[1]