Introduction to Compression


Having read the previous chapter, you should have begun to understand the real purpose behind the mastering process - the complete uncertainty of the consumers environment is what we have to overcome. Mastering aims to equip the track with the shape and sonic power to sound great on whatever medium it is finally played on.

So where does compression and limiting come into all of this? In the chapter 'Definition of Mastering', I explained that when playing my recordings at my friend's house, I had to play them at higher volumes (in comparison to commercial CDs) to be able to hear any of the finer details. The fundamental difference between my recordings and the commercial records was the dynamic range. By that I mean the difference between the loudest parts and the quietest parts.

Because the commercial CD's had undergone mastering, their dynamic range had been considerably reduced enabling all the quieter details to be made louder, without sounding as though they had been turned up. Let's imagine our listening environment when recording and mixing. As previously discussed, we are free from distraction, background noise and have relatively good quality speakers. In such an environment, a large amount of dynamic range wouldn't be so much of a problem - if a track happened to have some really quiet details amongst some louder ones, they would be heard fairly well in this environment. The consumer's listening environment is not likely to be so perfect. There will probably be background noise and distraction, also the speakers themselves could be inferior quality - laptop speakers being a good example. If the dynamic range of the music is too large, as in the quiet bits are too quiet compared to the loudest, then an amount of the music will struggle to be heard in such environments. By reducing the dynamic range and raising the level of the quieter details, we give the music a better fighting chance of being distinguished in the uncertainty of the consumer's environment. The main tools for carrying this out are compressors and limiters.

Aside from the very practical purpose of reducing the dynamic range, compressors can help 'glue' a mix together by bringing it to a whole. They also play another role in the way they can fatten up the sound of the music. One reason why they give this fattening effect is down to RMS energy. You will remember from the previous chapter on EQ, that RMS levels are closely proportional to our perception of loudness. RMS is a subject in itself, and quite a complex one. Later in this chapter I will explain what RMS is in layman's terms.

Before we get to all that, let's explore in detail how compressors work.

David Eley - TGM Audio

Next page... How Compressors Work