This is a follow-up to our popular article on EQ, "Thinking inside the box: a complete EQ tutorial"
, which was written by dnbscene co-founder Steve Mercer (aka hipnotic
). This article was written by Marc Crouch
, owner of dnbscene.com, and is intended as an accompaniment to Steve's article.
Ah, the compressor. This magical tool will fix all your volume problems and make your tunes instantly sound fat and professional. Just pull your tune into an audio editor, pick a "mastering" preset and whack the ratio up. Now play it back and... what's that? It sounds lifeless? There's a weird pulsing or "sucking" sound running through the track? Hmm, perhaps it's not as easy as that after all.
Compression is an oddly misunderstood tool in digital music production, and yet it is one of the two most essential processes you can apply to give your tracks that professional "full" sound. The other tool, of course, is EQ, knowledge of which is vital to effectively mastering the art of compression. As such, you should stop reading this tutorial if you haven't already got a good understanding of EQ. Better still, go and read our hugely popular in-depth EQ tutorial
first and then come back here, as I will be referencing some of the concepts from that article in this tutorial.
Now, let's lift the lid on this mysterious "compression" concept and get your tracks sounding loud and full.Part One: Grasping the concept
Ever since dnbscene.com Version 1.0
launched (way back in 2000), I have seen a question pop up in the production forums again and again: what is the difference between EQ and compression? Here's the simple answer: EQ deals with frequency
, compression handles volume
. The confusion tends to stem from the fact that playing with frequencies can impact volume, which is why it's important to have a solid grasp of EQ before trying to get your head around compression. Let's re-visit the "lid" from our multi-dimensional box referenced in the EQ Tutorial:
To recap: audio is represented by waves, and the height of the waves correlates to their loudness. The red lines (which we have referred to as the lid) represent the maximum amplitude the wave can reach before it starts to suffer. Go beyond the red lines and the sound will start to lose definition and start producing horrible side effects such as high pitched feedback and ugly distortion. This process is sometimes called "redlining" in the industry, and is a Very Bad Thing.
So, to get the optimum level of loudness we want to get our waveform's height up so that it's as close as possible to the lid without redlining. Referring again to our previous tutorial, this will make our "box" full and consequently make our track sound full.
Now, consider this waveform:
Here, the highest parts of the waveform (the ones touching the lid) are very narrow compared to the bulk of the waveform, meaning that the loudest parts are very short sections of sound. These "peaks" are often the result of particularly sharp individual hits such as a snare, vocal plosive (the popping noise you get when you record a "p" type sound into a microphone) or similar. On a complete track, they could be the result of EQ anomalies in specific places. Whatever the reason, the end result is that the average volume
of the waveform is pushed down (away from the lid) by those narrow peaks, as demonstrated by the yellow overlay here:
With the average volume sitting so far below the lid, the waveform will sound quite quiet overall to the human ear. To make it sound nicely loud, we need the rest of the track to be sitting closer to the lid where the peaks currently are. In other words, the average volume needs to be louder.
Now, we could just raise the volume of the whole waveform, but that would immediately push the peaks outside of the lid and create some nasty distortion. So the only option we have is to reduce the volume of those peaks so that they are more in line with the average volume, and then raise the volume of the entire waveform. This, in a nutshell, is what compression does. Here is a simplified example to illustrate:
With that explanation you should hopefully see why it's called compression, as on the most basic level it's about squashing (compressing) the loud peaks on a waveform to make the whole thing more even. It's the same as a human being moving a volume fader down during the volume peaks and then back up again during the quieter parts, but done automatically and much faster than a human hand can manage. An automatic volume control: that's basically, simplistically, what compression is.