D (musical note)
D[1] is a musical note a whole tone above C, and is known as Re within the fixed-Do solfege system. Its enharmonic equivalents are C
(C-double sharp) and E
(E-double flat). It is the third semitone of the solfège.
When calculated in equal temperament with a reference of A above middle C as 440 Hz, the frequency of middle D (D4) is approximately 293.665Hz.[2] See pitch for a discussion of historical variations in frequency.