Summary

In this tutorial we cover an interesting little fact that also experienced video editors are often not aware of: The beats of a song are not always located exactly at peaks visible in the waveform. Sometimes they are located slightly before or after them. In the tutorial we explain why this is the case and what practical implications it has when editing video to the beat.

Preview

Background

From time to time we get feedback for our automatic beat detection tool BeatEdit for Premiere Pro where users report that the beat detection is not accurate. When we investigate those issues, it turns out that the users expect the beat markers to be located exactly at peaks of the audio waveform. However this is not the case - for a good reason!

The beat is a 100% regular pattern or in other words, the time from one beat to the next one stays always the same, unless the tempo of the beat changes. However, for the peaks in the waveform there are many reasons why this is not the case. First of all, any music that is based on the live performance of a musician will never be 100% accurate. It is simply impossible to play an instrument and hit each beat without being off a few milliseconds. But much of the music we hear today is based on quantized midi data where the timing in theory should be 100% accurate. Does this mean that for those songs the beats perfectly lineup with peaks? No! Midi instruments are often based on sample libraries consisting of hundreds or thousands of recorded audio samples. And inside of those samples, again the peaks are often not aligned accurately.

Is this a problem? Not at all - having peaks slightly behind or before the actual beat does not sound odd. It is barely noticeable and maybe even adds some character to the song. The important thing to learn here is that you should not be irritated when the beat is located slightly before or after a peak. If you would shift the beat markers produced by BeatEdit to the nearby peaks, your result is not getting better, but worse: Because then the beats are not distributed evenly anymore. And this is what makes up the beat: That it is an accurate, regular repeating pattern.

Used Footage

NYC night aerials kindly provided by Artbeats

Song "Antidrum" by Dave Bode, Bodemedia

duration: 
7:34
all tutorials about: 

Comments

sorry to say, but your edit isn´t on the Beat. Your algorithm works in a straight mathematically way and ignores the FEEL of the Music, where, for example a "laid back" Groove isn´t uncommon. This "peaks" are the right points! This is a good Tool and a great starting point. But look at your "preview Tutorial". Do you really think that Video and Music are in a perfect match?

Thank you for your feedback!
I discussed this topic with various musicians and also with scientists working in the fields and the answers you get are a bit diverse. Probably this is related to what you say with the FEEL of the music. To a certain degree it is probably a matter of taste. Some people with a not so well-trained ear might not notice any difference at all and the experts have different opinions. One musician told me that it usually feels best, if the cut in the video happens slightly before the peak. Others told me that having it before is at least better than after the peak. Maybe this even depends on the style of the music.
For the next version of BeatEdit I consider to include tools to shift the beat markers in time. This will allow you to tweak the exact placement as desired.
Cheers,
Mathias

Hi Matthias,
Auch ich bin etwas entäuscht .. hatte ich doch wohl "peakedit" erwartet.
Auch wenn die Beats mathematisch korrekt liegen sieht es aus wie ein Schnnittfehler wenn der Cut erst kommt und dann im Song der Schlag auf die Snare.
Zur Zeit passe ich Beatedit immer noch manuel an - was ich eigentlich vermeiden wollte.
Ich warte ganz gespannt auf eine neue Version.
Hoffe das Update ist für Deine treuen Kunden dann "for free"
weiter so + liebe Grüße Björn

Hallo Björn, danke für das Feedback! Ob das Update kostenfrei wird, hängt davon ab, wieviel neue Funktionalität dazu kommt. Aber in jedem Fall sind die Updates bezahlbar.

Hi Mathias, great idea, sounds as an excellent compromise!

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