Part 3 – How to use compression for shaping transients

Compression in mastering is quite a misunderstood subject. It’s easy to think that compression is mainly used to control the dynamics and make the loud parts quieter in order to increase the overall level.

And sure, that happens at times. Some mixes are too dynamic and need to be controlled with some compression. This happens less often than you may think though. Many modern mixes actually have the opposite problem of not being dynamic enough.

Mastering engineers still like to use compression when mastering. The reason is something completely different than controlling the dynamics though.

Many mastering engineers use compression mainly to shape the transients.

The actual reduction of dynamics is usually an unwanted side-effect and there are tricks and methods to minimize that. We’ll get to that soon.

When a compressor is used for shaping the transients it can actually make the mix sound more dynamic. This is due to an increased clarity of the transients. When you hear engineers talk about how a compressor can add glue to the mix, this is usually what they are referring to.

In order to do this, we want to get as much shaping of the transients as possible from a compressor, while keeping the reduction of the dynamics to a minimum.

Different compressors will give different results, as will different attack, release and ratio settings. This is actually very easy to test! There is a simple, almost fool-proof method of setting up a compressor for mastering. Ready?

  1. Set the attack to approximately 10-50 ms and the release to 100-500 ms. The numbers are not that important, it’s just to get the controls to a sensible starting point.
  2. Set the ratio to 2:1
  3. Adjust the threshold so that you get approximately 0.5 dB of gain reduction during the loudest parts of the song. Stay well below 1 dB of gain reduction.
  4. Don’t add any gain, just leave the make-up gain at 0 dB. You want the compressed signal to be just as loud as, or slightly quieter than the bypassed signal.

The last two steps are the most important ones! You can now compare the sound with the compressor enabled and bypassed in order to decide what you prefer. By keeping the compressor at unity gain you have removed the loudness bias, and you are actually giving the slight loudness advantage to the bypassed signal. If the compressor is doing the right thing, the compressed version will sound better despite being slightly quieter.

This is so important that it needs to be repeated: A compressor used for mastering should make the mix sound better without making it louder!

By sticking to this simple rule, you will avoid the all too common pitfall of compressing too much. You will also train your ears to recognize the sound of compression on a full mix. This is something that we have all struggled with at some point. The fastest way to train your hearing is to avoid that make-up gain!

Now listen for how the transients sound. Are you getting a slight contour around the edges of the instruments? Are the drums getting punchier or snappier? Are the vocals more up front? Or is the opposite happening? Is the bypassed version the more exciting one? Be honest about this – you are only looking for actual improvements. Otherwise it’s better to leave the compressor off.

Try different attack and release settings or different ratios (remember to re-adjust the threshold to get 0.5 dB GR). Try with or without the stereo link. Try different compressors.

The effects can be subtle, but the more you do this, the more you will begin to pick up on the different characters that you will get from different compressors and settings.

You will probably find that very clean and transparent compressors may be too subtle for this kind of compression. Compressors with more character on the other hand will generally give better results when it comes to improving transient clarity.

Combine this compression strategy with getting the tonal balance right, and you will be well on your way to creating a great sounding master that will let your music shine brightly next to any other song in a playlist.

This compression strategy is also very useful for mixing as well! Try doing this trick on subgroups or individual instruments within your mix. You will find that small tweaks at the right places will add up to a great total improvement.

Another fundamental area of mastering is getting the high-end right. How can you achieve that smooth and yet clear high-end? We will have a look at that in the next part!

See you then!

💚 Sofia & Thomas