This is a chart that I made a while back showing the amount of time that a certain beat division lasts(which I call absolute duration) in a variety of tempos. I use it mainly to figure out how much time I’m working with when I compose, or try to determine the length of a tune while I put together a set-list.
- I color-coded tempos that are “tempo octaves” of each other. This essentially means that they are tempos at a 2:1 ratio. These tempos share the same absolute durations, but assigned to different beat values.
- To find the absolute duration of any triplet value, they should find the value for the same beat division, but in a tempo 150% the speed of the original tempo. For quintuplets, one should find the same beat division, but for 125%(5/4) the original tempo.
- To find the absolute duration of multiple measures, multiply as necessary. I tried to provide enough time values that it should usually only require multiplying by factors of 2 to get good approximations.
- In regards to quick calculation, I often generalize in the following ways:
- There are slow tunes, medium tunes, and fast tunes. For slow tunes(hovering around 60bpm), a measure of common time is about 4 seconds, so an 8-bar section would be 32 seconds, a 16 bar section is roughly a minute long, 24 bars is roughly a minute and a half.
- For medium tunes, a measure of common time is about 2 seconds, slightly over/under for slower/faster medium tunes(medium is a rather broad term). So a 16 bar section would be about 32 seconds. This can be closer to 40 seconds for a slower medium tune, or closer to 25 seconds for a faster medium tune. 24 bars would be 48 seconds +/- a few.
- Fast tunes hover around 1.5 seconds per measure of common time! For disgustingly fast be-bop on amphetamines tempos, it can even go lower. When this is the case, 16 bars of music amounts to 24 seconds, with faster tunes being closer to 20 seconds.
- The longer the length of time, the more it’s worth it just to do the calculation to be sure(you all have smart phones anyways). A musician’s estimate of the length of a tune can be horribly off. Perception of time during performance is unreliable.
- If estimating lengths for a set-list, factor in the inherent tendency to play things fast during live settings.