I have a lot of young artists that find me on AIM and ask me questions about mixing, so I figure I'll start a series of articles dedicated to audio as well as my dealings in the industry. There's a lot of people out there with a wealth of knowledge that are hoarding it and not using it themselves. I want to see artists grow in the underground. So I figured the way to help make a positive change is to let you know some of the stuff I know.
Today's first article is all about compression in the mix. So all you dudes out there just getting your feet wet in the home recording scene, this ones for you.
WHY YOU NEED COMPRESSION
Adding and using Compression is one of the most important processes in a recording or mix. It is vital and absolutely necessary. Basically, if you have recorded your tracks with no compression, and are attempting to mix further (also without compression)... you should be kicked in the dick meat. The dynamics of your recorded signal demand the control of compression. For example in your rhythmic hip hop vocals, some words are going to be louder and more accented than others, and will sometimes clip or red line. This is because you're an idiot. And have poor vocal technique. And quite possibly are using a cum sock for a pop screen. Im kidding. let's get serious for a minute though...
Compression reduces the volume of loud signal and increases the volume of quiet signal. This can be used to bring out subtle details, help control a vocalist with bad mic technique, limit distortion from loud transients, and force more consistent levels, making it easier to mix. Compression can also increase the average level of a track, effectively making it sound louder. Compression is a main reason why we hear modern music the way we do. Today's sound simply would not be what it is without compression. By the time you hear a song on the radio It's been hit in the mouth with a compressor around 4 - 5 times.
BASIC CONTROLS
There are a butt load of different types of compressors all with their own features and functions, but most compressors have a few similar basic controls: threshold, ratio, attack, and release. Less is more. Especially in the Audio realm. Having more control over your signal is good but not at the expense of time. You dont want to waste your precious time dicking with a million features on the latest and greatest piece of gear you bought because you want to be a tech nerd. Odds are.... the bullshit you're working on isn't that intricate and doesn't demand it.
In a way, a compressor is as auto volume adjustment. The compressor works by making the loud passages quieter and the quiet passages louder ("compressing" the dynamic range, so the variation from quietest to loudest is decreased). The threshold controls how loud the signal has to be before its volume is reduced. It's the point or volume level at which the compressors effects will kick in. Thus, setting the threshold high means that less compression will occur, because less of the signal will exceed the threshold to activate the compressor. That being said, a low threshold means that the compressor will do more, because more of the signal will exceed the threshold.
When the signal goes above the threshold, the gain of the signal is reduced by an amount controlled by the ratio control. For example, with the ratio set at 2:1, an increase in input of 2 dB above the threshold will result in an increase in the output of only 1 dB. Higher ratios yield more compression, but only to signals that pass above the threshold. Your results will vary, depending on what kind of compressor you are using. Some digital compressor plugins can make your track sound like C3P0's cock singing underwater. Always pay attention to what you hear as opposed to what you are looking at.
The attack and release controls work together with the threshold control to determine when compression will begin and end. If the signal is above the threshold for less time than the attack setting, then little or no compression occurs. Once compression is activated, it stays on for a length of time determined by the release control. So by setting a long (slow) attack, you can let through the first part of a loud sound. This is particularly useful because almost every note played on an instrument contains a little burst of energy, called the "initial transient". By setting the attack long enough to let the initial transients through, you can prevent the compressor from squashing the life out of the recording. So if your compressed tracks sound lifeless, try a longer attack setting. On the other hand, setting the attack too long can squash your track and make it sound like the compressor kicked on and didn't shut off.
Most of the time you will be using compression to reduce the dynamic range of your signal, which means that you will be reducing the difference between the loud sections and the quiet sections. Compression, therefore, can increase the average volume of the track without increasing the maximum volume. It sets a ceiling while raising the floor so to speak.
TWEAKING FOR DUMMIES
Let's start with reducing dynamics. Of course, every unit and every track is different, but I generally start by setting the ratio low, around 1.5:1, the threshold high, and both the attack and release somewhere in the middle. I then bring the threshold down until I can hear that the compressor is reducing the signal. From there, I usually tweak the controls little by little until I'm golden. For hip hop vocals I usually set my attack very low from the original settings. I like my compression to ebb and flow with the tempo of the lyrics.
Attack and release times should generally correspond to the speed of the instrument. For example, bass tracks should normally use slow attack and release times while drum tracks usually sound best with fast times. When adding compression to a mix, rather than an individual track, I generally recommend fast attack and release times, though other engineers will insist that you use slow attack and release times. Usually most agree that it's best to keep the ratio low: too much compression on a mix will squash your mix like a fat kid on a twinky.
*always remember that too much compression will mess up the logarithms of the mix's equalization. thus altering the EQ of your mix.
OTHER USES (the rest of this was taken from an unknown source online)
Besides reducing dynamics, compression has a pile of uses, and sometimes a reduction in dynamics may be motivated by something in particular, such as a poor performance or an uneven mix. Some of the tricks of compression involve the use of the compressor's side-chain, which is a special signal path that is only used for controlling the compressor. For example, if you put a high-pass EQ on the side-chain, the compressor would become more sensitive to high-frequency content than low-frequency content, and work harder to reduce the signal whenever the signal had a lot of high-frequency content.
Compensating for a Poor Performance: Compression can often be used to overcome weaknesses of the performer. For example, experienced singers move away from the mike when they sing loudly and towards the mike when they sing softly. Less experienced singers generally don't do this at all or, even worse, do the opposite. Even with an experienced singer, it can be desirable to get that "close-miked" sound even during the loud passages. Other instruments suffer, too: it can take years of experience to play evenly and with carefully controlled dynamics. Sometimes even great musicians will do a great take with bad dynamics. In all these cases, compression is essential because the dynamic range of the performance is wider than it should be and compression can bring it back into the correct range.
De-essing: A compressor forms the basis for another effect called a de-esser. A de-esser is used for reducing the so-called sibilant sounds of vocalists, such as "s", "th", and "f", which often have highly exaggerated high-frequency response in recordings. The best thing is always to try getting rid of as much sibilance as possible by using appropriate mike technique, but since this isn't always possible, most engineers like to have a de-esser handy. Note that you can create your own de-esser by using an EQ with a compressor. See the Compressor description for details on doing this in XO Wave.
Ducking: Ducking is a little different from compression: instead of reducing the gain based on the volume of the signal going through it, a ducker reduces the gain based on another signal. For example, you could use ducking in a podcast to reduce the volume of music when someone is speaking. Note that in XO Wave, Ducking is done with the special Envelope Generator effect instead of a compressor.
Compressing a Whole Mix: Compressing a mix is different from compressing a single track because every instrument gets compressed the same amount. In practice, this often means that the bass instruments cause the whole mix to get over-compressed, which makes it sound like the bass instruments are "punching out" the other instruments. Many compressors, including XO Wave's, offer compensation for this. If not, you can compensate by using the compressor's side-chain feature with an EQ.
Compression As a Special Effect: Sometimes compression just sounds cool and that's all there is to it. A lot of hip-hop samples, for example, are heavily compressed. It often sounds good because tiny details suddenly become prominent, while the loud sections are still under control. Compression can also soften the edges of distortion, and enhance performance nuances.
Compression to Increase Dynamic Range: After all this talk of reducing and controlling dynamic range, it may seem strange that compression can also be used to increase dynamic range, but it can be a great tool for this as well. Often a track, such as a snare drum, may sound great by itself, but may have a hard time competing with other instruments in the mix. To help it cut through, you can add a little compression with a relatively long attack time. This reduces the volume of most of the snare drum sound, but keeps the initial transient loud. This short burst of sound is often all a snare drum or other percussion instrument needs to sound great in the mix. Depending on your gain setting, this technique can do two things: it can increase the volume of the transient, helping the track to stand out, or it can reduce the volume of the rest of the note, which may help un-clutter a dense mix.
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