Master bus limiter "lookahead": what's that *for*, anyway?
If your audio engineering learning experience has been anything like mine, you might have spent a lot of time not knowing exactly what the lookahead knob on a master bus limiter was for. So I thought I’d share my observations!
First: what is lookahead? It’s actually really simple, in concept — it’s simply a short delay that gets added to the audio that we hear a tiny bit — relative to the audio that the limiter uses for processing, which remains undelayed — so that the limiting happens ever so slightly *before* the sound that’s actually triggering the limiting.
For example: imagine you have a kick drum in your mix, and every time it hits, the master bus limiter is limiting it some amount of decibels. Now imagine that we adjust the limiter’s lookahead to 1.5 ms. All this means is that the limiting now kicks in 1.5 ms before the kick drum hits. Kind of like magic!
It’s always good to know what’s going on under the hood, but it doesn’t necessarily tell us much in terms of what it does to the sound, which is the more important thing. Here are two things that I use it for:
It’s like a volume knob (or maybe a clarity knob?) for the kick drum. As you increase the lookahead, the limiter puts an increasing amount of space between the onset of the limiting and the kick drum hit. This carves out a tiny bit of quieter space before the kick drum attack, which seems like it gives each kick drum hit its own little pocket in which to be heard more clearly.
This effect is more pronounced the more you increase the lookahead time; you can to a large extent sweep the knob to find the ideal place for your kick drum to sit front to back in your master. If you want the kick to recede more and get glued into the mix more, try a very short lookahead — maybe 0.5 ms or so. If you want the kick to come forward on the soundstage and be more defined, try increasing it — somewhere between 1.5 and 2.5 ms might be a good place to listen.It can reduce distortion. When you’re hitting your master bus limiter hard — I’m talking like 5-8 dB on peaks, depending on the material and the limiter — certain sounds can cause the limiter to distort. Sounds with a lot of midrange harmonic content can do this — think fretless bass, or cello, or viola, or a big Moog synthesizer.
If you have sounds like this prominently in your mix, and it’s a loud mix, and you’re hitting your master bus limiter kind of on the hard side, and you’re hearing some crackling on passionately-played notes — try increasing the lookahead. (The limiter is being asked to do the limiting with too quick a reaction time, and that’s what’s making the distortion.) Basically just turn the knob to the right until the crackling goes away!
Do you have any other uses for lookahead? Message me, I’d love to hear them! — jamie