E-MU 1212M PCIe - Manual (Page 68)

5 - Effects
Core Effects Descriptions
68 Creative Professional
Compressor
In its simplest form, an audio compressor is just an automatic gain control. When the
volume gets too loud, the compressor automatically turns it down. Compressors are
useful in musical applications because they allow you to record a “hotter” signal
without overloading the recording device.
Since the compressor turns down the gain of the signal, you might wonder how can it
make the signal level stronger. A Post Gain control allows you to boost the output gain
of the compressor in order to make up for the gain reduction. The overall level is higher
and only turned down when the signal level gets too loud. This level is called the
Threshold, which just happens to be the most important control on the compressor.
In
Out
Threshold
Ratio
Attack Release
Post Gain
Signal path = Stereo
VCA
Level
Control
Delay
Basic Controls
The three main controls of a compressor are the Ratio control, the Threshold control and
the Gain control.
If the signal falls below the Threshold, no processing will take place. Signals exceeding
the Threshold will have gain reduction applied as set by the ratio control. This
important control allows you to dial in the range of amplitudes you want to tame. For
example, if you’re trying to trim off just the loudest peaks, set the threshold so the gain
reduction meter only shows compression during these peaks. One of the biggest
mistakes in using a compressor is having the threshold set too low. This adds noise as
the compressor will always be reducing the volume.
The Ratio control determines how strongly the compressor will affect the signal. The
higher the ratio, the more reduction will be applied. If the ratio is high enough, (above
10:1) the signal will effectively be prevented from getting any louder. In this situation,
the compressor will be acting as a Limiter, placing an upper limit on the signal level. In
general, ratios from 2:1 to 6:1 are considered compression and higher ratios above
10:1 are considered limiting.
The Post Gain control amplifies the signal after it has been compressed to bring it back
up in volume. If you don’t increase the gain, the compressed signal will be much lower
in volume.
Two other important controls are Attack and Release. Attack controls how quickly the
gain is turned down after the signal exceeds the threshold. Release controls how fast
the gain is returned to its normal setting after the signal has fallen below the threshold