A tempo map is a part of a
MIDI
Musical Instrument Digital Interface (; MIDI) is an American-Japanese technical standard that describes a communication protocol, digital interface, and electrical connectors that connect a wide variety of electronic musical instruments, ...
file. Musical events occur as a succession of events in time, whose speed is
tempo
In musical terminology, tempo (Italian for 'time'; plural 'tempos', or from the Italian plural), measured in beats per minute, is the speed or pace of a given musical composition, composition, and is often also an indication of the composition ...
. Music also organizes these according to a framework called
meter
The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of of ...
, by partitioning time into patterns of "strong" and "weak" beats. MIDI's tempo map specifies the speed at which a file's events are transmitted within this framework: their tempo. If a file plays at a fixed tempo, its map is a horizontal line (e.g., measures 38 and 39 in this part of a MIDI
sequencer’s display of the end of J.S. Bach's prelude #8 from Book I of the
Well-tempered Clavier
''The Well-Tempered Clavier'', BWV 846–893, consists of two sets of preludes and fugues in all 24 major and minor keys for keyboard by Johann Sebastian Bach. In the composer's time ''clavier'' referred to a variety of keyboard instruments, ...
):
But, if the tempo fluctuates as a function of time, such as in ''
accelerando
''Accelerando'' is a 2005 science fiction novel consisting of a series of interconnected short stories written by British author Charles Stross. As well as normal hardback and paperback editions, it was released as a free e-book under the CC ...
'', ''
allargando
A variety of musical terms is encountered in printed scores, music reviews, and program notes. Most of the terms are Italian, in accordance with the Italian origins of many European musical conventions. Sometimes, the special musical meanings ...
'', or ''
rubato
; , , ;) is a musical term referring to expressive and rhythmic freedom by a slight speeding up and then slowing down of the tempo of a piece at the discretion of the soloist or the conductor. Rubato is an expressive shaping of music that is a p ...
'', the line is respectively an upward- or downward-climbing one, or in the latter case, a complex curve, as seen here in measures 35 and 36 at left, or the ending in measures 40 and 41.
In most music, aesthetics demand that this flow of events not be linear, but fluctuate according to the expression the music intends to convey. Hence, a very emotional piece such as the preceding is excerpted from, although playing at a base tempo of MM=50 — which means 50 quarter notes per minute, holding back or lunging forward according to expressive impulse can result in a tempo map similar to that seen above: It flexes tempo down for the intermediate cadence at left, and again for the final
allargando
A variety of musical terms is encountered in printed scores, music reviews, and program notes. Most of the terms are Italian, in accordance with the Italian origins of many European musical conventions. Sometimes, the special musical meanings ...
at the right.
After recording a sequence in real time at a fixed tempo, or composing it using step-record mode,
MIDI sequencer
A music sequencer (or audio sequencer or simply sequencer) is a device or application software that can record, edit, or play back music, by handling note and performance information in several forms, typically CV/Gate, MIDI, or Open Sound Contr ...
software may have functionality to edit the MIDI tempo map, so as to result in a natural, expressive result, not a machine-like one, when playing the file.
MIDI
{{Sound-tech-stub