Creating A Look-Ahead Compressor

**This week’s article is split into 2 sections; what a look-ahead does & how to make a look-ahead for a compressor without the function**

When looking at a compressor, most of us are familiar with the basic controls such as; ratio, threshold, attack, etc. However, some compressors/limiters come with a feature known as the “look-ahead”.

What does this function do?

This function magically looks into the future, analyses the upcoming signal, and triggers the compressor to start compression earlier than the occurring transient. Well actually…this isn’t completely true. This function can’t really “see into the future”. Instead, it allows a compressor to react to a signal earlier, by means of a side chain. Therefore, if a compressor is at its fastest attack and it still lets transients through, you can use the look-ahead to fix that.

How does it work?

The look-ahead function duplicates the incoming signal, which is then delayed (by the amount that you set the lookahead value). The non-delayed signal is fed to a side-chain that drives the compression of the delayed signal. That signal is then outputted with the rest of the tracks. (The downside is that the output will be slightly delayed by the amount you set the lookahead)

Why is this function useful?

There are a number of reasons to why one might want to use this feature when mixing/mastering. The look-ahead function is a great tool for dealing with transients. It allows you to theoretically have an attack that is “below 0 seconds”. It is useful as it prevents an engineer from having to compromise between using a slower attack time (smoother gain changes) and faster attack rates which are capable of catching transients. So now you can get the best of both worlds.

What can this function help with?

  • Brick-wall Limiting / Hard Limiting: Using look-ahead would prevent any peaks from passing through. It prevents transients from taking any headroom.
  • Mastering: Just as a final precaution when mastering you could use a lookahead to make sure that you don’t have any sound clipping the output. It also helps if you’re trying to participate in the loudness wars (Turn it up to 11!)
  • Punchier: This technique can be used to get some punch out of a track and bring out sustain in an element. When using parallel compression, you can use a look-ahead when compressing the parallel bus, which blends with the original track to achieve a punchier sound.
  • A slower attack with an early look-ahead time can allow you to save transients when applying compression. This way a smooth-sounding slower attack rate can be used to catch transients.

Making a Look-Ahead function?

Let’s say you’re mixing and you need a little look-ahead to help out, but your compressor doesn’t offer that function…WHAT DO YOU DO?

Most DAW’s come with a compressor that allows you to use a side-chain (if you’re not sure what a side-chain is or what it does, check out Mitchell’s article on side-chaining). Here are the steps to setting it up.

  1. Duplicate the track that you wish to affect.
  2. Set the duplicated track to “No Output”
  3. Nudge the duplicated track earlier (the earlier you nudge the track is equivalent to the higher you would set the look-ahead value)
  4. Add a compressor on the original track (must have the ability to use a side-chain)
  5. Create a send from the duplicate track and use it as the key on the compressor from the original track. (Note that on some compressors, you have to activate the key detector so that the compressor looks at that signal)
  6. Adjust the Parameters


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