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Theory

One-line octave

The one-line octave covers the notes C4 to B4. It holds middle C and the standard pitch A4 at 440 Hz. In the older German system the stroke at the top right of the letter counts the octaves upwards (c′ to h′); today the number system C4 to B4 is more widely used.

Range
C4 to B4
Older notation
lower-case letter with one stroke: c′, d′, e′ …
Middle C
C4
Standard pitch
A4 = 440 Hz
Scientific
C4 to B4 (A4 = 440 Hz)

One stroke per octave

Because the seven note names repeat in every octave, you need a way of writing that shows which octave a note lies in; the page Reading music uses numbers (C3, C4, C5). Besides that there is an older German system. In it the great octave (C, D, E …, capital letters) and the small octave (c, d, e …) are the two next lower ones. Above them follows the one-line octave with one stroke (c′), then the two-line octave with two (c″). In the scientific system, used throughout this glossary, the octaves are numbered instead: the one-line octave is the fourth, so C4 to B4, and the C4 at its start is middle C.

The one-line octave

C D E F G A B 1 1 ½ 1 1 1

From C4 to B4. Middle C (C4) and the standard pitch A4 are marked. In the treble clef C4 lies on the first ledger line below the staff, in the bass clef on the first ledger line above it.

Middle C and standard pitch

C4 joins the two staves of the piano: in the treble clef it sits on the first ledger line below, in the bass clef on the first above. The note A4 is the standard pitch. The page Tools says that the tuner works at A4 = 440 Hz.

On the guitar

The high E string sounds at 329.63 Hz as E4, so in the one-line octave (frequencies as given on the page Tools). Guitar music is, according to the symbol library, usually written without the small 8 and still sounds an octave lower than written. The names of the octaves therefore refer to the sound, not to the written notation.

Try it yourself: In Notes on the Fretboard you name notes on the guitar. According to the exercise text, you find the note A there on the A string at the twelfth fret, on the D string at the seventh, on the G string at the second and on the B string at the tenth. Only the last one is A4 at 440 Hz in the one-line octave; the other three sound an octave lower, at 220 Hz.

Continue on Maikstrings

Reading music

Octave registers, clefs and note names step by step.

Tools

Tuner with the standard pitch 440 Hz and the guitar strings.

Notes on the Fretboard

Find and name notes on the guitar.

Related terms

Small octaveGreat octaveStandard pitchOctaveClefC clefLedger line

Editor: Maik Krohm · reviewed on 3 October 2026

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