“Re (musical note)” redirects here. For its use in movable-do system, see Solfège. D is a musical note a whole tone above C, and is known as Re within the fixed-Do solfege system. An enharmonic note is C, which is a diatonic semitone below D. When calculated in equal temperament with a reference of A above middle C as 440 Hz, the frequency of middle D (D4) is approximately 293.665 Hz. See pitch for a discussion of historical variations in frequency.