Beats per minute
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Beats per minute (bpm) is a unit typically used as either a measure of tempo in music, or a measure of one's heart rate. A rate of 60 bpm means that one beat will occur every second. One bpm is equal to 1/60 Hz.
Beats per minute became common terminology in popular music during the disco era because of its usefulness to DJs, and remain important in dance music. Hip-hop typically uses a BPM tempo of 70-110, while house music is faster: 110 -140BPM. Jungle music goes even faster: 140-190, while Gabba tops it with above-200 BPM and Speedcore with 200-700 BPM. These values are general guides, however, and should not be interpreted as absolute.
Beatmixing, an art amongst DJs, concerns the speeding up or down of a record in order to match the BPM of a previous track so both can be flawlessly mixed. Normally, the pitch and BPM of a track are linked: spin a disc 10% faster and both pitch and tempo will be 10% higher. Software processing to change the pitch without changing the tempo, or vice-versa, is called time-stretching or pitch-shifting. It works OK for small adjustments (+- 20%), but the result can be noisy and unmusical for larger changes.
BPM can be calculated by hand (count the number of downbeats/bass drums per 60 seconds, or - to be fast - per 15 seconds and multiply by 4), but some software programs such as MixMeister (http://www.mixmeister.com), Traktor-DJ (http://www.native-instruments.com/index.php?traktormixer_us) and PC-DJ (http://www.pcdj.com/Products/RedBlueVRM.asp) can do it automatically.
External links
- Online Metronome (http://www.visionmusic.com/metronome/tempo.html)
- Online BPM measurement (http://www.all8.com/tools/bpm.htm)
- Convert BPM to Hz/ms (http://www.smoothouse.org/projects/hizmo/bpm.asp)cs:BPM
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