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).
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.
This music theory article is a stub.