D♯ (D-sharp) or re dièse is the fourth semitone of the solfège.It lies a chromatic semitone above D and a diatonic semitone below E, thus being enharmonic to mi bémol or E♭. However, in some temperaments, it is not the same as E♭. E♭ is a perfect fourth above B♭, whereas D♯ is a major third above B. When calculated in equal temperament with a reference of A above middle C as 440 Hz, the frequency of the D♯ above middle C (or D♯4) is approximately 311.127 Hz. See pitch (music) for a discussion of historical variations in frequency.