Sol, So, or G is the fifth note of the fixed-Do solfège starting on C. As such it is the dominant, a perfect fifth above C or perfect fourth below C.
When calculated in equal temperament with a reference of A above middle C as 440 Hz, the frequency of Middle G (G4) note is approximately 391.995 Hz. See pitch for a discussion of historical variations in frequency.
It has enharmonic equivalents of F (a diatonic semitone below G♯) and A (a diatonic semitone above G♭).