With a frequency around 261.6 Hz, middle C is designated C4 in scientific pitch notation because of the note's position as the fourth C key on a standard 88-key piano keyboard. (Another system known as scientific pitch assigned a frequency of 256 Hz to this note. While numerically convenient, it is not used by concert orchestras.) While other note-octave systems (including those used by some manufacturers of digital music keyboards) may refer to "Middle C" with a different designation, the C4 designation is the most commonly recognized in auditory science, and in musical studies it is often used in place of the Helmholtz designation c'. In MIDI, it is note number 60.
While the expression "Middle C" is generally clear across instruments and clefs, some musicians tend to use the term to refer to the C note in the middle of their specific instrument's range. For example, C4 may be called "Low C" by someone playing a Western concert flute (which has a higher and narrower playing range than a 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.
Within vocal music the term Soprano C, sometimes called High C or Top C, is the C two octaves above Middle C. It is so named because it is considered the defining note of the soprano voice type. It is also called C6 in scientific pitch notation (1046.502 Hz). In Helmholtz notation, it is c'''.
The term Tenor C is sometimes used in vocal music to refer to C5 as it is the highest required note in the standard Tenor repertoire. The term tenor C can also refer to an organ builder's term for small C or C3 (130.813 Hz), the note one octave below Middle C. In stoplists it usually means that a rank is not full compass, omitting the bottom octave.
The term Low C is sometimes used in vocal music to refer to C2 as it is usually considered the dividing line between true basses and bass-baritones. A true basso can sing this note easily while other male voices, including bass-baritones, cannot.
For the frequency of each note on a standard piano, see piano key frequencies.
Designation by octave
|Scientific designation||Helmholtz designation||Bilinear music notation||Octave name||Frequency (Hz)||Other names||Audio|
|C-1||C͵͵͵ or ͵͵͵C or CCCC||(-uC)||Subsubcontra||8.176||)|
|C0||C͵͵ or ͵͵C or CCC||(-vC)||Subcontra||16.352||)|
|C1||C͵ or ͵C or CC||(-wC)||Contra||32.703||)|
|C5||c′′||(yC)||Two-lined||523.251||Tenor C (vocal), Treble C||)|
|C6||c′′′||(xC)||Three-lined||1046.502||Soprano C (vocal), High C (vocal), Top C (vocal)||)|
|C8||c′′′′′||(vC)||Five-lined||4186.009||Eighth octave C||)|
Twelve just perfect fifths (B♯) and seven octaves do not align as in equal temperament.
- Pythagorean: 701.955 × 12 = 8423.46 = 23.46 = B♯+++
- ET: 700 × 12 = 8400 = 0 = B♯ = C
- 1200 × 7 = 8400 = 0 = C
This difference, 23.46 cents (531441/524288), is known as the Pythagorean comma.