C (musical note)
C (Italian, French: Do) is the first note of the C major scale, the third note of the A minor scale (the relative minor of C major), and the fourth note (F, A, B, C) of the Guidonian hand, commonly pitched around 261.63 Hz. The actual frequency has depended on historical pitch standards, and for transposing instruments a distinction is made between written and sounding or concert pitch.
Historically, concert pitch has varied. For an instrument in equal temperament tuned to the A440 pitch standard widely adopted in 1939, middle C has a frequency around 261.63 Hz (for other notes see piano key frequencies). Scientific pitch was originally proposed in 1713 by French physicist Joseph Sauveur and based on the numerically convenient frequency of 256 Hz for middle C, all C's being powers of two. After the A440 pitch standard was adopted by musicians, the Acoustical Society of America published new frequency tables for scientific use. A movement to restore the older A435 standard has used the banners "Verdi tuning", "philosophical pitch" or the easily confused scientific pitch.
Middle C (the fourth C key from left on a standard 88-key piano keyboard) is designated C4 in scientific pitch notation, the most commonly recognized notation in auditory science, while both C4 and the Helmholtz designation c′ are used in musical studies. Other note-octave systems, including those used by some makers of digital music keyboards, may refer to Middle C differently. In MIDI, Middle C is note number 60 which equates to C5.
While the expression Middle C is generally clear across instruments and clefs, some musicians naturally use the term to refer to the C note in the middle of their specific instrument's range. C4 may be called Low C by someone playing a Western concert flute, which has a higher and narrower playing range than the piano, while C5 (523.251 Hz) would be Middle C. This technically inaccurate practice has led some pedagogues to encourage standardizing on C4 as the definitive Middle C in instructional materials across all instruments.
In vocal music, the term High C (sometimes less ambiguously called Top C) can refer to either the soprano's C6 (1046.502 Hz; c′′′ in Helmholtz notation) or the tenor's C5; both are written as the C two ledger lines above the treble clef but the tenor voice sings an octave lower. The term Low C is sometimes used in vocal music to refer to C2 because this is considered the divide between true basses and bass-baritones: a basso can sing this note easily, whereas other male voices, including bass-baritones, typically cannot.
(20,000 hertz is the start of the ultrasound in healthy young adults.)
Traversing the circle of fifths can result in a B♯ that is higher than C by 23.46 cents, the ratio of twelve just perfect fifths (B♯) to seven octaves being 531,441 / 524,288, the Pythagorean comma. A B♯ that is three just major thirds above C is lower than the octave by an interval called a diesis, 125:128 or 41.06 cents.