Octave

The octave above or below an indicated note is sometimes abbreviated 8a or 8va (Italian: all'ottava), 8va bassa (Italian: all'ottava bassa, sometimes also 8vb), or simply 8 for the octave in the direction indicated by placing this mark above or below the staff.

For example, the C major scale is typically written C D E F G A B C (shown below), the initial and final Cs being an octave apart.

The use of such intervals is rare, as there is frequently a preferable enharmonically-equivalent notation available (minor ninth and major seventh respectively), but these categories of octaves must be acknowledged in any full understanding of the role and meaning of octaves more generally in music.

Among the most common are the scientific, Helmholtz, organ pipe, and MIDI note systems.

In scientific pitch notation, a specific octave is indicated by a numerical subscript number after note name.

In this notation, middle C is C4, because of the note's position as the fourth C key on a standard 88-key piano keyboard, while the C an octave higher is C5.

Any of these directions can be cancelled with the word loco, but often a dashed line or bracket indicates the extent of the music affected.

The human ear tends to hear both notes as being essentially "the same", due to closely related harmonics.

Notes separated by an octave "ring" together, adding a pleasing sound to music.

[10] Leon Crickmore recently proposed that "The octave may not have been thought of as a unit in its own right, but rather by analogy like the first day of a new seven-day week".

[12] Studies have also shown the perception of octave equivalence in rats,[13] human infants,[14] and musicians[15] but not starlings,[16] 4–9-year-old children,[17] or non-musicians.