Compression is one of the most important and useful types of processing, especially when mixing and mastering. Compression is often misunderstood and therefore misused and if there's one thing about compression its that when it's used badly it sounds absolutely terrible and will put any listener off immediately. You can get some cool effects from creative compression but there will be more on that in other tutorials. This tutorial will guide you through the basics of using a compressor explain what its does to the sound, what the different parameters do and when you should use it, plus some tips to get you going.

What is compression?

Compression is part of a group of processors called dynamic processors. It's sisters and brothers are EQ, noise gates and limiters. The basic way compression works is to bring the whole gain (volume) of a track up to more even level by compressing the gain of the louder parts, therefore making the quieter parts seem louder in comparison to the louder parts. For example lets say you have a bass guitar part which playing a funky bassline were some of the notes are much quieter than the others and it doesn't sound right. Compression would bring up the gain of the quieter notes therefore making the whole bassline sound tight, punchier and the dynamics even. This is the main thing compression does but there are many techniques in which it changes the sound in a different way but we'll cover them in detail in a different tutorial.

Parameters

Understanding what each parameter does is important to being able to use compression properly and also gives you the power to manipulate it to create your own sounds. The actual names displayed here may differ from plugin to plugin but they all do the same thing.

Threshold

The threshold is possibly the most important parameter when using compression as it controls how the whole processing works and effects the sound of the audio the most. Threshold basically means the threshold, measured in dB, at which the compressor will start to compress. In other words this means any signal from your audio file that goes over the threshold in volume will be compressed and have it's gain reduced (hence gain reduction).

For example if your audio file's average volume is -5 dB and your compressor's threshold is -10 dB, then every time your audio file plays back over -10 db the signal will be compressed. Lowering the threshold will compress more of the sound and generally makes the compressing more audible. See the diagram to the right which shows the threshold and original gain.

The threshold is set by starting at 0db and lowering it untill the difference between the quiet parts and loud parts sounds right. In others stop lowering the threshold when the quiet parts are loud enough, unless you want the sound to be over compressed, but more on that in another tutorial. Confusing i know but you'll soon get the hang of it.

Ratio

Ratio is often very misunderstood but it's not really that complicated. The ratio parameter is the ratio of how many dB's of gain increase you will get for every dB of gain you reduce or compress. So for example you might have a ratio setting of 1:2, so if you compress the signal by 1 dB it will increase the signal gain at the output by 2dB. Take one db off get two back. This really controls the how aggressively the compressor will compress, the higher the ratio the more aggressive the compressor works. Some instruments won't need as aggressive compressing as others, for example an acoustic guitar won't need as higher ratio as a kick drum. Got that? Right well on to the easier stuff now.

Make up gain

The make up gain control is very simple and almost extinct in plugins because of auto make-up gain but still useful. When you compress the signal you are reducing the gain of the signal, the make up gain is there to increase the gain back to the right level. It's not a volume control so don't use it like one. Check the gain of the signal before compressing and use the make up gain once you've finished tweaking the compressor to bring the signal back to it's original gain. Use the bypass switch to check there right.

Attack

Attack, measured in ms, is a very simple control which you might have seen something similar on a synth. It controls how long the compression waits to start gain reduction after the signal has hit the compressor threshold. So if its set to 100 ms, the compressor won't start compressing untill 100 ms after the signal hits the threshold. You might think a 100 ms is nothing but it can make a difference to how the compressor works.

Release

Very similar to attack but backwards. Release is how long the compressor carries on compressing the signal after it's dropped below the threshold.

Meters

Most if not all software and hardware compressors have some sort of metering system which graphically shows how much of the signal is being compressed (gain reduction meter), the compression curve and the final output meter. These are very useful especially when learning how to use compression as it shows you visually what's going on. When your learning your ears won't be trained as well as an expert user so you might find it hard to gauge how much gain reduction is needed. Well this is where the meters come in but remember to use your ears and never rely on just the meters alone. Your not painting, your making music.

Conclusion

So now you the basics of how to use a compressor. All you have to do now is start trying them out! Try different ratios, threshold levels and experiment with the attack and release controls and see what you come up with. I will cover more advanced techniques in different tutorials.

Tip

Remember to always listen carefully. I know that sounds stupid but it's harder to do than you think especially with computer screens which distract your senses. Try mapping the controls to a midi controller then turn off or cover your computer screen and adjust the settings using your ears. I bet it will surprise you with what you come up with.

Zander

Akai MPK25 review

Published: 15. 05. 2008     10 comments

We take a look at the Akai MPK25 midi controller, the smallest of the Akai MPK series of midi controller/keyboard/MPC drum pad/trigger. This is a feature packed controller and promises a lot but does it live up to it's creators repretation?