In addition to the usual parameters that you’re used to using on a compressor like threshold, ratio, attack and release, some compressors also have a ‘look ahead’ function. In this article, we’ll look at what ‘look ahead compression’ does, why it’s so useful and how to use it.
What does look ahead compression do?
Look ahead compression effectively allows your compressor to see the signal a few moments in advance of it being processed. This allows the compressor to react to the forthcoming level changes earlier.
Why use look ahead compression?
Look ahead compression can be really useful. That’s because with some compressors, even when you set them to their fastest attack time, they are simply not quick enough to react to very fast transients. What’s more, very fast attack times can sometimes yield unnatural sounding results. So look ahead compression let’s you achieve the smoother and more natural sound that you would associate with slower attack times, whilst still capturing very fast transients in your audio signals.
How does look ahead compression work?
If your compressor offers a ‘look ahead’ function, then when you enable this option, the signal going into your compressor is duplicated. The duplicate version of the signal is delayed slightly, usually by between 1 and 10 milliseconds. Meanwhile, the non-delayed signal is fed to a side chain.
It is the non-delayed signal that the compressor reacts to. But it is the delayed signal that the compression is applied to.
Because the signal that is going to be processed by the compressor doesn’t arrive until a few milliseconds after the non-delayed signal has told the compressor what to do, the compressor is effectively able to look ahead and react to changes in advance of them happening.
At this point, you may be asking yourself this… if the signal coming out of the compressor is delayed, will my track sound out of time? Because the delay applied to the signal is so small, you shouldn’t be able to hear a difference. That said, the time change could potentially create phase issues that did not previously exist. But even then, most modern DAW’s have built in automatic delay compensation to correct latency introduced by plugins. So this should eliminate this problem.
How to set up look ahead compression if your compressor doesn’t have this function built in
It’s quite straightforward to set up look ahead compression using a compressor that doesn’t have a look ahead function built in. Begin by duplicating the track that you want to use look ahead compression on. You will use the duplicated track to drive the compressor. Meanwhile, the compression itself will be applied to your original track.
Next, move the duplicated track back so that it plays earlier in the timeline. 5 to 10 milliseconds is a great starting point, but you can experiment to find the best results. Be sure to mute the duplicate track. You don’t want to hear this track in your mix. You’re simply using it to tell the compressor how to process the original track.
Create a send from the duplicate track by assigning it an available bus. Make sure that you set the bus to ‘pre fade’. This ensures that the signal is still sent via the bus even with the channel muted. Insert a compressor on the original track. Finally, set the compressor’s side chain input to the bus that you have assigned the duplicate track to.
Now, the compressor will react to your duplicate track which is playing the track a few milliseconds early. But the compressor will be processing the audio on your original track.
Do you use look ahead compression in your mixes?