In music, tempo is the speed or pace of a given piece or section. In classical music, tempo is typically indicated with an instruction at the start of a piece (often using conventional Italian terms) and is usually measured in beats per minute (or bpm). This means that a particular note value – usually a quarter note or crotchet – is specified as the beat, and that the number of beats per minute then specifies the rate of flow. For example, a tempo marking of Allegro con brio indicates that there should be 120 crotchets or quarter notes per minute.
Tempo may be separated from articulation and meter, or these aspects may be combined under the term “ritmo”. In jazz and popular music notation it is common to see metronome markings which state both the number of beats per minute and also indicate what kind of note should receive one beat: for instancequarter = 120 means that there are four beats per minute, each one marked by a quarter note.
While the ability to precisely control tempo has always been desirable in musical performance, it was only with the advent of mechanical clocks in the 13th century and player pianos in 1876 that accurate constant tempo became possible. Before these devices were invented musicians used varying speeds to create different effects; for example slower tempos might create a feeling of sadness while faster ones might evoke feelings joy. The average human heartbeat provides another source of natural variation: it can range from 60-90 bpm, though most people have heart rates between 70-80 bpm.
Aristotle writes about rhythm in his treatise on poetry: “Some rhythms are appropriate for young men [and women], others for old; some rhythms are appropriate for citizens [and] others for foreigners …” He also gives several examples where different kinds of feet produce different effects when they occur at different places within various typesof meter. Horace’s Ars Poetica contains similar observations: “The iambic trimeter … will not do … if you want your verses to sound like those written by Catullus.”
During most of history detectives have had little success using tempo analysis to solve crimes because criminals seldom leave behind recordingsof their crimes… However more recently computer programs have been developed which automatically compare recordings made at crime scenes with vast databases containing known recordings such as speeches by politicians or songs from commercial CDs. These programs can often find matches even when there are only slight similarities between two recordings.