Sounds scary doesn’t it? But dynamics processing is an essential first step when it comes to mixing. Before you start applying EQ and effects, panning and automating, and generally getting stuck in to the song, you need to tidy everything up and get it in line. This is where dynamics processing comes in. What we want to do is to tame the dynamics of the recordings, and make sure that we don’t have bits that are very quiet and can’t really be heard in the mix, and then parts that suddenly jump up in volume and pounce out of the mix. In short, we want balance and control.
There are four processors that are used to tame dynamics: compressors, limiters, gates, and expanders.
*De-Essers are also thrown in to the dynamics group. These are basically frequency selective compressor/limiters that are used to remove sibilance from vocals and other harsh hi-frequency sounds – more on de-essers in the near future
A compressor does what it says on the tin; it compresses the dynamics of a recording. Limiting is just very heavy compression (some consider 10:1 ratio compression as limiting, others consider much higher amounts like 20:1 limiting).
Compressors and limiters work on the signal above a set threshold level, and only kick in and start working when something makes the mistake of exceeding that threshold level.
Whereas compression has a smooth approach to reducing peaks above the threshold, limiting cuts it off without regard for its feelings.
Controls on a compressor/limiter vary from model to model, but I’ll address the most common controls.
A threshold dB level is set and the compressor/limiter works on everything above this threshold. Basically, say you set the threshold to -3dB, everything above this threshold level is reduced in volume to bring it back within the threshold level.
This sets the ratio of compression (no prizes for guessing that). For example, a ratio of 2:1 will provide 1dB of reduction for every 2dB of signal above the threshold, so it will be half as loud on output after compression.
Attack sets the speed at which the compressor/limiter reacts to the signal. You’d think that this should be set for a fast attack to catch peaks before they cause a problem, but very fast attack times will compress the pick strike on guitars and the initial attack of drums, making things sound too soft and rounded with no attack. So a lot of the time, you want to set the attack so that it comes in after the initial strike. Release controls how fast the compressor lets go, so on busy passages or faster songs, you want the compressor to do its job and get back out of the way before the next note is played. Hold controls how long the compressor stays on before the release steps in and takes it out again.
Soft knee/hard knee
This refers to the threshold curve. A soft knee is a gentle slope – a gentle approach to dealing with the target signal. A hard knee is a drop-off – a fast and severe approach to dealing with the target signal (the target signal being what is above the threshold with compressors and limiters, and below the threshold with gates and expanders).
Considering that by compressing, you are bringing the loudest parts of the recording down in volume to sit beneath the threshold you’ve set, it’s not going to be as loud as it was before. So, by using the makeup gain, you bring the output from the compressor back up to the original volume of the recording. A bypass button can be utilised to listen to the recording uncompressed, then you can switch the compressor back in and match the volume with the makeup gain.
Where compressors and limiters work on signal above a set threshold, gates and expanders work on signal below a set threshold. They also share a similar relationship as compressors and limiters, an expander reacts smoothly to a signal (like a compressor) whereas a gate reacts harshly to a signal (like a limiter). An expander lowers the signal of anything below the threshold, and shares much of the same controls as a compressor. The attack, release, hold, and output gain are used in much the same way. A gate works in the same way as an expander, except that it completely cuts any signal that falls below the threshold. You would use an expander on a guitar track with pickup hum or ground loop noise so that it smoothly lowers the level as soon as the signal falls below the threshold, so the guitar part sounds natural and unaffected in the mix. A gate used on the same part would chop off anything below the threshold and would be very noticeable as a cut in the mix.
Every recorded instrument undergoes dynamics processing, and it can get fairly complicated. There are different compression techniques such as side-chain compression and parallel compression, and each instrument requires a different approach. However, this all comes with experience and necessity, and it will of course, be discussed in this blog when we move on to more advanced recording techniques in the future.