Duration
The temporal extent of a note.
What it means
Duration is one of the basic properties of a note, alongside pitch, volume, and tone colour. It designates how long a note sounds. In musical notation it is not given absolutely but as a ratio: the note values say how the durations relate to one another, and only the tempo marking connects this ratio with real time.
Musical use
Between notated and sounding duration there is a difference that is considerable in practice. A quarter note designates the time until the next event, not necessarily the time in which the note sounds: articulation decides whether the note fills this space or occupies only part of it. Staccato shortens, legato fills out, tenuto holds. Instruments also behave differently — a piano note dies away by itself, a wind instrument sustains it evenly, a bell rings on beyond the notated duration.
On the level of larger contexts, duration determines the rhythmic shape and thereby an essential part of the musical character: the same sequence of notes in other values yields a different music. In mensural notation the ratio of the values to one another was variable and had to be fixed by mensuration signs; the present-day system rests throughout on halving.
The duration of the single note is to be distinguished from the tempo, which concerns the speed of the course of events, and from agogics, which means small stretchings and shortenings in performance.
Alongside pitch, volume, and tone colour, duration counts as one of the four basic parameters of the note. In the serial music of the 1950s it was ordered in series like the other parameters. In notation it is the most precisely fixed parameter: note values, dots, ties, and tempo markings determine it.
Performance practice
Take care to really sustain long notes — they are almost always taken too short, especially before an entry. With every articulation marking, check how much of the notated duration is actually to sound, and keep this uniform within a passage. And practise rhythms separately from the pitches by tapping or speaking them; duration is the part that is neglected first when reading.