J & L trimming or asymmetrical trimming, as it as also known, is one of the most essential keys to driving an edit. There are many online resources showing how to make a J or an L trim, some less confused than others.

However, there is very little in the way of theory behind how asymmetrical trimming can be used. And I am not a gut-instinct person, I want to know how and why it works. So, I have worked out a few principles that can be applied when using asymmetrical editing that may be helpful to those starting out, and may challenge those more experienced editors who have built up editing instincts for trimming to think about why it is their cuts feel right.

1. J cuts are simply better than L cuts.

As you can see from the video the J cut (where audio precedes video) effectively creates a need in the viewer to see who is speaking. This is called “motivating” a cut. If the task of the editor is to remain invisible (which it is, no argument will be entered into here, thank you very much) then creating a need in the viewer to see the image we are going to cut to is very effective in making the cut feel natural / invisible.

Using a J cut of as little as 3 frames can be enough to motivate, and therefore hide, a cut. You can cut right in the middle of the first word if you need!!!

2. Motivating your cuts is effective even when the aim is to surprise.

Because I have no real social life, I once carefully watched a scene from Red Dragon cut by cut to work out how they had cut it so well. This was when I first noticed just how awesome J cuts are – every single cut was a J cut, whether it was a creak of a floorboard, or a whistle of wind, every cut was motivated by a sound cue. This might seem counter intuitive, to signal a change in shot when the objective is to unnerve and surprise but the principle remains the same. Surprise is heightened by suspense and suspense can only happen if you signal it and if the viewer is drawn into the scene, so it is still very important for the editor to be invisible.

What’s more, each motivated cut is essentially a tease for the inevitable fatal cut.

3. Phantom J cuts.

You can use the principle of the J cut to motivate b-roll cuts as well. A soundbite might be part of a continuous interview section, but if it relates to a piece of b-roll you can use it to motivate the cut in the middle of a b-roll scene. For example bringing in interview audio under a b-roll scene can allow you to cut seamlessly to a shot of the speaker in-scene rather than in-interview. You can even use a J cut to mask an interview jump cut (from interview shot, to the same interview shot). This requires some nuanced timing, but if done well, your viewer will not notice the cut at all.

4. The trouble with L cuts.

You may notice as I did with the video example of the L cut (where video precedes audio) that this did not feel like a natural cut, it felt jarring. This is because no need was created in the viewer, the cut was not motivated. A way to create this need would have been to ramp the audio of the sea up before the cut – effectively creating a J cut with the atmospheric sound.

5. Audio motivation and Conceptual motivation.

One way to make an effective L cut is to create a conceptual motivation, by mentioning for example the word “sea” or “beach”. But there is a difference however between using conceptual motivation and audio motivation. Audio signals are meant to be invisible, and therefore we benefit by purposefully cutting while our attention is on something else, so you should make these cuts in the middle of speech, in the middle of a word in fact. Where as conceptual signals need to feel purposeful so if you are relying on a word like “sea” or “beach” to signal a change of scene to a beach, you should wait until a break in the audio after the word has been mentioned. These cuts are much more intentional, so are typically used to change location / scene, or to signal a new topic in a documentary, and in a narrative film might be used for comic effect.

6. Conceptual motivation in dialogue.

With dialogue scenes in narrative film L cuts no longer have conceptual imagery to signal a change of shot, instead we have reaction to what is being said, if we can motivate the viewer to want to know what the person being spoken to feels about what is being said then we are free to (L) cut to their reaction while the speaker is still speaking. This sort of cutting is a complex area of its own and not my specialty. As with the Red Dragon example, J cuts are liberally used in narrative film, because they just feel right.

But… Why does it feel right?

Well, because of some pretty fundamental aspects of human perception. For one, you can get away with bringing in audio early through slow transitions over time, where as this is not possible with video, unless you want your edit littered with cross-dissolves.

Ghastly.

And this is ghastly for a reason, we don’t see cross dissolves in reality, they are wholly artificial, but we do hear the slow increase in volume of a person, a car, or a wave approaching. It is a natural human experience to hear someone say something of interest and for us to then direct our visual attention to them, but the opposite is not true, we don’t see someone talking and then hear what they are saying, that’s not the way hearing works. Short of putting our fingers in our ears, in general we involuntarily hear things, and we purposefully look at things. So these are fundamental aspects of the nature of vision and hearing that can inform the way we recreate those natural experiences through editing.

An editor will always find a point where naturalism is not the objective, and sometimes an editor grows tired of always being invisible. But knowing the natural way to edit something and the reasons why that method of editing feels natural will help in any attempt to subvert that naturalism.