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Filed under: Audio •Editing •Motion Graphics •

The Magic Tempos

Vibrations in a sound’s wave happen at a much faster pace than frames happen in video or film. Likewise, a musician may pick a tempo where the peaks of these vibrations - the beats in the music - don’t land on nice, even frame boundaries. However, there is a way to determine tempos that exactly line up with frames. If you can get your composer to use them, your job spotting the audio will be much easier later; you can even animate at these paces without hearing the music, knowing it will line up later.

When working with visuals, we often pick a tempo in terms of how many frames per beat (“fpb”) we want to time our animations or cuts against. To work this backwards to a tempo, take your frame rate (i.e. 30) times the number of seconds in a minute (i.e. 60), and divide the result (i.e. 60 x 30 = 1800, or 1798.2 for 29.97 fps NTSC, 1500 for 25 fps PAL, and 1440 for 24 fps film) by your desired fpb number. The result is tempo in beats per minute (“bpm”), which most musicians understand.

It is very common for us to animate at 15 fpb for video, which works out to the sprightly dance tempo of 120 bpm at 30 frames per second. A lot of music is actually a little slower than this; a very good number to use is 16 fpb (112.5 bpm). As it turns out, even numbers of frames per beat are especially nice, since they are easier to divide by two into sub-beats; fpb values that are multiples of two (2, 4, 8, 16, etc.) keep dividing all the way down to tiny musical intervals in convenient whole numbers of frames, giving you lots of choices of how to time your hits to line up with sub-beats in the music.

If you give a musician a tempo such as 112.5 bpm, they may ask you to round it off to something like 112, or ask if it’s okay if they change it to something close like 110 – especially if they are not familiar with creating music for visuals. Although this will make life easier for them, the answer should be “No.”

The reason is that their adjusted tempo again will no longer divide into a whole number of frames per beat, and your hit points and keyframes will have to wander back and forth between 16 and 17 frames per beat. Patiently but firmly explain to them that you have a much coarser tempo resolution than they do; you have to live with it, and it would be nice if they could live with it too for the sake of the project. This will not be news to a seasoned video or film music composer, but it often is to a normal musician or composer.

The table below shows a list of “perfect tempos” in bpm that translate to whole numbers of frames per beat. If negotiating a tempo ahead of time with a musician, give him or her this list and ask them which one would be most appropriate for their piece. Remember that even numbers of frames per beat give you the most options:

The list of Magic Tempos you want to hand a musician who is composing music for you to animate or edit to.

(I’ve included tempos calculated at both 30 and 29.97 fps for video; you might be working in computer-only animation instead of video, and can therefore use the cleaner 30, or your musician might have equipment that can perform the 29.97/30 0.1% fudge for them so they can work at “30” and let their gear slow everything down to 29.97 to compensate.)

Before you have the finished music, you might find it helpful to create a “click track” based on the tempo you have selected. You can then render this simple audio track against your video drafts and animation proofs to see how things are working out.

Keep this click track simple; anything that begins to sound like real music (i.e. like another actual song) might take you down a path other than the one the musician is traveling, and can make your producer or client get the wrong idea of what the finished music is going to sound like. We have found that a simple pop or click on every beat, plus an additional louder sound on the start of the measure (i.e. the downbeat), works well.

Again, remember that rules such as these are just guidelines; if the project asks for it, break them. Many great pieces of music don’t stick with a steady tempo, and many great animations have floated in time relative to musical hits. Let your ears and emotions be the final judge.

The content contained in our books, videos, blogs, and articles for other sites are all copyright Crish Design, except where otherwise attributed.

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