From en.wikipedia.org:
[Sign that indicates the relative duration of a note] right
In music notation, a NOTE VALUE indicates the relative duration of a note,
using the texture or shape of the _notehead_, the presence or absence of a
_stem_, and the presence or absence of _flags/ beams /hooks/tails_.
Unmodified note values are fractional powers of two, for example one,
one-half, one fourth, etc.
A rest indicates a silence of an equivalent duration.
** List
{| class="wikitable sortable" |- !class="unsortable"|Note
!class="unsortable"|Rest !American name !British name !Relative value
!class="unsortable"|Dotted value !class="unsortable"|Double dotted value
!class="unsortable"|Triple dotted value |- ||70px ||x50px || colspan="2"
|large, duplex longa, or maxima[1][2]<br>(occasionally _octuple note_,[3]
_octuple whole note_,<ref name=256th/> or _octuple entire musical note_)[4] ||
8 || 8 + 4<br>= 12 || 8 + 4 + 2<br>= 14 || 8 + 4 + 2 + 1<br>= 15 |-
|File:longa.gif || File:longa rest.svg || colspan="2" |long<ref
name="Baker131" />[5][6] or longa[7]<br>(occasionally _quadruple note_[8] or
_quadruple whole note_)<ref name=256th/> || 4 || 4 + 2<br> = 6 || 4 + 2 +
1<br> = 7 || 4 + 2 + 1 + [1]<br> = [7] |- |x20px || File:breve rest.svg ||
double whole note,[9] double note[10][11][12] || breve || 2 || 2 + 1<br> = 3
|| 2 + 1 + [1]<br> = [3] || 2 + 1 + [1] + [1]<br> = [3] |- |x15px || x70px ||
whole note || semibreve || 1 || 1 + [1]<br> = [1] || 1 + [1] + [1]<br> = [1]
|| 1 + [1] + [1] + [1]<br> = [1] |- |x70px || x70px || half note || minim ||
[1] || [1] + [1]<br> = [3] || [1] + [1] + [1]<br> = [7] || [1] + [1] + [1] +
[1]<br> = [15] |- |x70px || x24px or x16px || quarter note || crotchet;
semiminim || [1] || [1] + [1]<br> = [3] || [1] + [1] + [1]<br> = [7] || [1] +
[1] + [1] + [1]<br> = [15] |- |x70px || x30px || eighth note || quaver || [1]
|| [1] + [1]<br> = [3] || [1] + [1] + [1]<br> = [7] || [1] + [1] + [1] +
[1]<br> = [15] |- |x70px || x50px || sixteenth note || semiquaver || [1] ||
[1] + [1]<br> = [3] || [1] + [1] + [1]<br> = [7] || [1] + [1] + [1] + [1]<br>
= [15] |- |x70px || x70px || thirty-second note || demisemiquaver || [1] ||
[1] + [1]<br> = [3] || [1] + [1] + [1]<br> = [7] || [1] + [1] + [1] + [1]<br>
= [15] |- |x70px || x70px || sixty-fourth note || hemidemisemiquaver || [1] ||
[1] + [1]<br> = [3] || [1] + [1] + [1]<br> = [7] || [1] + [1] + [1] + [1]<br>
= [15] |- |x70px || x70px || hundred twenty-eighth note ||
semihemidemisemiquaver[13][14] (rare) || [1] || [1] + [1]<br> = [3] || [1] +
[1] + [1]<br> = [7] || [1] + [1] + [1] + [1]<br> = [15] |- |x70px || x70px ||
two hundred fifty-sixth note || demisemihemidemisemiquaver<ref
name=256th>Kartik Asooja, Sindhu Kiranmai, and Paul Buitelaar "UNLP at the
C@merata Task: Question Answering on Musical Scores ACM (see
http://csee.essex.ac.uk/camerata/unlp_asooja_long_14.pdf) " (rare) || [1] ||
[1] + [1]<br> = [3] || [1] + [1] + [1]<br> = [7] || [1] + [1] + [1] + [1]<br>
= [15] |}
Shorter notes can be created theoretically _ad infinitum_ by adding further
flags, but are very rare.
** Variations
The breve appears in several different versions.
Sometimes the longa or breve is used to indicate a very long note of
indefinite duration, as at the end of a piece (e.g. at the end of Mozart's
Mass KV 192).
A single eighth note, or any faster note, is always stemmed with flags, while
two or more are usually beamed in groups.[15] When a stem is present, it can
go either up (from the right side of the note head) or down (from the left
side), except in the cases of the _longa_ or _maxima_ which are nearly always
written with downward stems. In most cases, the stem goes down if the
notehead is on the center line or above, and up otherwise. Any flags always
go to the right of the stem.
right
** Modifiers
A note value may be augmented by adding a dot after it. This dot adds the
next briefer note value, making it one and a half times its original duration.
A number of dots (_n_) lengthen the note value by [2<sup> _n_ </sup> − 1] its
value, so two dots add two lower note values, making a total of one and three
quarters times its original duration. The rare three dots make it one and
seven eighths the duration, and so on.
The double dot was first used in 1752 by J. J. Quantz;[16] in music of the
18th century and earlier the amount by which the dot augmented the note
varied: it could be more or less than the modern interpretation, to fit into
the context.<ref name=":0" />
The _vertical_ double dot was introduced by Willi Apel and is commonly used in
modern transcriptions of medieval and renaissance music. It lengthens an
already dotted note by half: a dotted half note (minim) consisting of 6
quarter notes becomes 9 quarters when vertically double-dotted. This greatly
simplifies modern notation (which otherwise would require a dotted half note
tied to a dotted quarter note).
To divide a note value to three equal parts, or some other value than two,
tuplets may be used. However, see swung note and notes inégales.
** History
*** Gregorian chant
Although note heads of various shapes, and notes with and without stems appear
in early Gregorian chant manuscripts, many scholars agree that these symbols
do not indicate different durations, although the dot is used for
augmentation. See neume.
In the 13th century, chant was sometimes performed according to rhythmic
modes, roughly equivalent to meters; however, the note shapes still did not
indicate duration in the same way as modern note values.
*** Mensural notation
Around 1250, Franco of Cologne invented different symbols for different
durations, although the relation between different note values could vary;
three was the most common ratio. Philippe de Vitry's treatise Ars nova (1320)
described a system in which the ratios of different note values could be 2:1
or 3:1, with a system of mensural time signatures to distinguish between them.
This black mensural notation gave way to _white mensural notation_ around
1450, in which all note values were written with white (outline) noteheads.
In white notation the use of triplets was indicated by _coloration_, i.e.
filling in the noteheads to make them black (or sometimes red). Both black
and white notation periodically made use of ligatures, a holdover from the
_clivis_ and _porrectus_ neumes used in chant.
Around 1600 the modern notational system was generally adopted, along with
barlines and the practice of writing multipart music in scores rather than
only individual parts. In the 17th century, however, old usages came up
occasionally. <!-- Here's an example from 1692, by Marc-Antoine Charpentier:
-->
** Origins of the names
The British names go back at least to English renaissance music, and the terms
of Latin origin had international currency at that time. _Longa_ means
'long', and many of the rest indicate relative shortness. _Breve_ is from
Latin _brevis_, 'short', _minim_ is from _minimus_, 'very small', and _quaver_
refers to the quavering effect of very fast notes. The elements _semi-_,
_demi-_ and _hemi-_ mean 'half' in Latin, French and Greek respectively. The
chain semantic shift whereby notes which were originally perceived as short
came progressively to be long notes is interesting both linguistically and
musically. However, the _crotchet_ is named after the shape of the note, from
the Old French for a 'little hook', and it is possible to argue that the same
is true of the _minim_, since the word is also used in palaeography to mean a
vertical stroke in mediaeval handwriting.
** References
[reflist]
[Musical notation] [Musical note values] [Rhythm and meter]