Many folks are confused by the concept of limiting, and/or how to use a limiter. An old mentor of mine used to liken a limiter to a governor on a car. “Son,” he would say in a thick southern accent, “a governor ensures you can only drive so fast and no faster. This way, those damn cops will never give you a speeding ticket again!”
Well, a limiter does just that with audio. It allows you to have only a certain amount of signal level passing a threshold and no more. Think of it as an incredibly brutal compressor. Whereas a compressor gradually takes down the peaks in a smooth manner, a limiter cuts them off at the knees.
So the question remains, how do I best use such a powerful tool? Here’s how it works. . . .
Basically a limiter has only a few parameters you can adjust, although the amount of control varies from manufacturer to manufacturer:
· Output Volume (which is sometimes called the ceiling).
· Threshold (which is sometimes called the input).
· Release (which is how fast you want the limiter to let go of the sound).
A good limiter has no sound to it. Just like a guillotine, it is precise and clean. Like its cousin the compressor, it has a compression ratio that is preset to a very high number of 10:1 or more, and it also has a very fast attack.
For the ultimate in stopping sound, there are now tools called “brick wall limiters,” where the ratio is set to infinity:1. I find this a little silly— mostly because, in my world, I only use a limiter when I want to create a brick wall. Otherwise, I use different dynamic processing.
Part of the fullness of modern day mixes is the saturation of the limiter. The more dB you toss into it, the louder and denser the mix sounds—even though it has a ceiling of sorts. Almost every modern record has multiple limiters in one place or another. It is one of the hallmarks of modern recording technique. (I wonder if 100 years from now, when people listen back to the recordings done today, they laugh at us for the absurd lack of dynamics? I know I would!)
Two Limiting Applications
Squashing the master bus. The most obvious thing that comes to mind would be to place a limiter on the master bus to avoid peaks in a program. It is used that way for radio and television, in order to keep all of the programming in line so everything is delivered in a consistent volume range.
As an example, let’s check out the Waves L1 Ultramaxizer. First, place the plug-in on the Master Bus out. It should always be the last effect in the chain. Set the Out ceiling to –3.5dB. This means the mix will never get louder then –3.5dB of digital zero. Next, set the Threshold to –12.7. This should give it a bit of density, and bring many things that were not as prevalent in the mix to the forefront. Then, set the release to –10, just to make it a bit more transparent.
Taming bass players. For this one, I used a Digirack compressor/limiter. Digidesign is one of those manufacturers that like to have the engineer do more of the work, so we will have more controls to change. (They like to call it options!) Set your output ceiling to –1. Let’s make this sucker work for a living! Set your ratio to 12.5:1—remember, for true limiting, you must be at least 10:1 or above. Now, we are going to want this guy to move very fast so it doesn’t get in the way of the mix. I set my attack at 7ms, and my release at 60ms. The input I have crammed down a bit, because I don’t want this part jumping out at all—set it to 21.2dB. Lastly, I set up my knee (the actual bend in the response curve that represents the move from uncompressed/unlimited to compressed/limited. This I set at 18dB—sort of middle of the road.
These two tips should get you started on the road to limiting. Just remember, a limiter draws a metaphorical line in the audio sand.