Compressing
Dynamic effects change and control the aspects of volume in a recording. While not as dramatic as reverb and chorus, dynamic effects are some of the most important tools in recording — and the ones that are easily forgotten or misused in home recording. Dynamic effects come in a few flavors: compressing, limiting, and gating.
Dynamic effects are subtle and don't alter the character and tone of a sound; they affect only volume, and only in a subtle way. If you slap on a reverb, you can instantly tell what's going on. Something changes right away. Grab an EQ knob and you impart some change immediately. But with dynamic effects, you get a less obvious change.
A compressor is an effect that automatically stops volume from rising too high. When instruments spike their volume wildly, as drums and bass do, for example, the sound can be unpolished and hard to listen to. A compressor, when set correctly, keeps sudden volume changes from occurring. It compresses the loud signals, makes them less noticeable, and smoothes out the overall volume level of a track.
Compression has many uses in the studio. It controls instrument levels when you're tracking. It helps bring tracks to a smoother volume level when you're mixing. It also compresses the entire song to smooth out the volume when you're mastering.
Let's take a drum track, for instance. Drums produce a wide range of sounds, from very soft to quite harsh. In other words, their dynamic range is pretty wide. In order to set the volume level correctly, you need to account for the loudest hits and make sure they don't clip the channel. This can be a challenge and usually means turning down the track, which can make the softer parts harder to hear. Applying a compressor limits the loudest hits from getting too loud and lets you raise the overall level of the track without fear of clipping. This helps make the drums fit into the mix better and also serves to smooth out the sound. This is one of the most common uses of compression.
Parameters
A typical compressor has a few controls that set how the compressor acts. FIGURE 14-2 shows the Waves Renaissance Compressor plug-in for a visual example.
FIGURE 14-2
Waves Renaissance Compressor
Gain: Sets the overall volume of the plug-in. When using a compressor, it's typical to boost the gain because you will have more volume range at the top to work with.
Threshold: Sets how loud the incoming signal needs to be before the compressor starts to work. The lower the threshold (in negative numbers), the more signals get squashed.
Attack: Controls the length of time (measured in milliseconds) the compressor takes to actually start to change the sound level after the volume reaches the threshold.
Release: Controls the length of time (in milliseconds) the sound should be held by the compressor after the volume level falls below the threshold.
Ratio: Here is the most important parameter! The ratio is the difference between incoming and outgoing signal. A 3:1 ratio says that when 3dB of sound come past the threshold, an increase of only 1dB comes out the other side. Ratios of between 2:1 and 4:1 will sound natural. Any higher and the dynamic range may sound “squashed” and quite unnatural.
How to Use a Compressor
Setting up a compressor isn't hard; you just need to be aware of a few parameters that help it to sound natural. The threshold should not be set so low that the compressor is always working. You really want to compress only the upper end of the dynamic range. The ratio depends on how much fluctuation the source has. If it's a snare drum, you might want a 4:1 ratio or even higher. If you're trying to lightly compress a guitar track, choose a lower ratio. Attack and release are where compression is won and lost. Attack is not as critical as release. If the release is long, then the instrument will sound unnatural. You have to listen for the instrument's natural volume decay and try to match that with release time. As mentioned before, compression is not a dramatic effect, and it might take you quite a while to hear if it's even there.
Try bypassing your effects often to hear the before and after material. This way you can judge how you're doing. Bypassing effects is commonly referred to as A/B testing. (“A” is with the effect on, and “B” is without any effect.)
