Configuring compression can be a daunting task. In this post I’ll show you how to do it quickly and easily – like a boss!
Let’s first understand the parameters of a variable threshold compressor
- Threshold: Audio level above which compression sets in. Signals below the threshold do not get compressed.
- Ratio: The amount of compression applied once a signal exceeds the threshold. Low ratios (2:1), little compression – high ratios (10:1), lots of compression.
- Make Up Gain: After applying compression your signal is generally quieter than before. This is not very desirable because you will need to re-adjust your faders afterwards. Wouldn’t it be easier to do this volume adjustment right inside the compressor? The make up gain parameter allows you to do just that, thus aiming at a compressed sound that has the same perceived volume as the uncompressed.
- Attack / Release time: These are also called the time constants of the compressor. They attack time determines how fast or slow a compressor begins to work once an audio signal exceeds the threshold. The release time determines how fast a compressor eases out of gain reduction once the signal falls back below the threshold.
Other parameters that you might encounter
- Knee: The hard- or softness with which the compression sets in. With a ‘hard knee’ compression immediately starts once an audio signal exceeds the defined threshold. With a ‘soft knee’ compression starts gently (i.e. with a lower ratio) slightly below the defined threshold. Then the ratio slowly increases until the nominal ratio that you dialled in has been reached, usually slightly above the defined threshold.
- Model / Type: Analog compressors can be built using various operational principles. The most common models are opto, FET (field effect transistor) and VCA (voltage controlled amplifier). The type of circuitry used influences the sound of the compressor. In plug-ins that offer this control you can change between different emulations to tweak the sound.
Now let’s tweak those parameters
Initial setup – configure attack, release and knee
Set threshold to 0dBFS (or the maximum value available) and the ratio to 1:1. This ensures that the compressor is doing nothing since no signal in the digital realm can exceed 0dBFS and a ratio of 1:1 means not applying any compression even if a signal would exceed your threshold. Now set the initial attack and release times as well as the knee (if you have, err, your compressor has one) according to the following guidelines:
- Vocals: Attack: 5-10 ms, Release: 500 ms or auto, Knee: soft.
- Drums / other percussive elements: Attack: 1-5 ms, Release: 250 ms or auto, Knee: hard.
- Guitars (acoustic): Attack: 10 ms, Release: 500 ms or auto, Knee: soft.
- Guitars (electric): Attack: 5-10 ms, Release: 500 ms / auto, Knee: hard.
- Strings: Attack: 10 ms, Release: 500 ms or auto, Knee: soft.
There’s a thread that’s going through here. You can use it to come up with initial values for any other instrument:
- Slow attack (~10 ms) and release (~500 ms) times make the compressor ‘softer’. If you have an instrument that is supposed to sound natural with ‘invisible’ compression – go for slow time constants. A slow attack sounds more natural since it generally lets the initial transient pass uncompressed, thus preserving much of the original tonal quality. A slow release sounds more natural since you will avoid heavy ‘pumping’ of the compressor upon returning to zero gain reduction.
- Faster attack and release times help you to contain your dynamics better. Material with strong transients (percussion, drums, bass) might need faster time constants to tame the dynamics. However, a faster attack sounds more aggressive since your initial transients will be compressed. Fast release times can increase the pumping effect of a compressor in the release phase.
- Last but not least a soft knee makes your compressor… well… softer.
Next step: Set the appropriate ratio
Use the following guidelines to determine the ratio (amount of compression applied to signals above the threshold):
- Material that needs gentle compression (vocals, acoustic guitars, strings) goes well with settings of 2:1 – 4:1.
- Material that needs more taming (drums, bass) works well with settings between 5:1 and 10:1.
- Again, a low ratio makes the compressor sound gentler and / or more ‘invisible’.
You’re almost there! What’s missing is setting the amount of gain reduction using the threshold. Now it’s a good idea to keep a close eye on the gain reduction meter! Start with 6 dB of gain reduction and tweak to taste. Again, instruments that need a ‘heavier hand’, or if you are after a ‘more compressed’ sound you may want to reach for a gain reduction of 10 dB or even more.
Last but not least – increase the make-up gain until your compressed signal has the same perceived volume as your uncompressed one. Important: Avoid clipping at this stage (watch the red lights of your mixer / plug-ins).
This is your initial setup – now go tweak
As with any mix processor you now should evaluate your compressor in the context of the mix. Put all tracks back in the mix and check whether the compressor improves the instrument you have been adjusting. If you feel that the dynamics are now smoother and the element blends in better – good job! If you feel that you are compressing too much or too little, tweak threshold and ratio.
Last but not least try adjusting the sound of the compressor with the attack and release times. That’s it! With this routine you will be able to set up your compressors much faster – without relying on presets!
A final note
This post is about setting up compressors to control the dynamic range of your material. In some cases you may be trying to achieve a certain ‘punch’ or ‘fullness’ by using compression. This means you are no longer using the compressor just to control the dynamics – you are using it actively to shape the sound of your instrument. In this case you may wish to go for some more extreme settings (i.e. more compression). Remember that the more your compressor goes into gain reduction the more you bring out its sonic character.
Don’t overdo it! Beware while compressing – don’t squash things too much! Compressors are dangerous in the sense that compressed sounds are more pleasing to our ears during short time intervals.When listening for extended periods of time, overly compressed material is fatiguing and no pleasure to listen to. Remember that you can always apply compressors at the submix stage. Ah, and there’s mastering as well…
That’s it for today! If you liked the post – how about checking out my podcast?
Until next time – make some noise!