E♭ (E-flat) or mi bémol is the fourth semitone of the solfège. It lies a diatonic semitone above D and a chromatic semitone below E, thus being enharmonic to D♯ (D-sharp) or re dièse. In equal temperament it is also enharmonic with F. However, in some temperaments, D♯ 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 E♭ above middle C (or E♭4) is approximately 311.127 Hz. See pitch (music) for a discussion of historical variations in frequency.