1.2 What Is a Compressor-Limiter?
A compressor is a device that helps control the dynamic range of a track
you’re recording or mixing. Example: if you’re recording a vocal and the singer
is going from very soft to very loud, a compressor can make the loud parts not
quite as loud. Then you can turn up the overall level of the vocal to hear the soft
parts better. As a result your vocal will have a more consistent level in your mix,
while still retaining its expressiveness. Compressors are also frequently used on
guitars, bass, piano, and other instruments for the same reason - to record a
consistent level that will hold its place better in your mix. Used sparingly a
compressor is transparent - the listener can’t hear it working. Used poorly it can
suck all the life out of whatever you’re recording, and that can’t be undone by
any amount of later processing. Some people will use compression aggressively
as an effect, and that’s perfectly valid if it’s what you want. Always listen and
keep an eye on the gain reduction meter. Try aiming for -3dB to -5dB of
compression as a starting place when recording a vocal. Remember: you can
add more compression later, but you can’t take it away.
When mixing many engineers use a stereo compressor to run the entire
mix through. It can make your mix more aggressive and more alive sounding,
more integrated. “Glue” is a term many engineers use for mix compression.
Again, too much compression can ruin your mix, so use your ears.
A limiter is a compressor with a higher ratio (greater than 10:1) that
literally puts a limit on how loud you can make something. It comes from the
days of radio when there was a legal limit to how loud a broadcast could be, but
radio stations still wanted to seem as loud or louder than their competitors. A
limiter raises the average level of a track or mix while not letting the peaks go
beyond a fixed level - into the red, for instance. Like compression, limiting can
make your mix more exciting or ruin it completely. Listen!
There are four basic types of compressors: Tube, Optical, FET and VCA.
You may be familiar with our popular FET Compressor, the FET III. VCA
compressors don’t have a great reputation among professional engineers for
good reason - they are mostly feed-forward designs utilizing cheap RMS
detector chips and low-quality monolithic current-to-voltage convertors. The
Comp IIT is a very different, more complex VCA design that uses feedback, a
peak detector and an all-discrete Class A follower. We use the VCA like a FET
to get the sound we all love without the thermal instability and other problems
associated with FETS.
