10.6

85Logic Pro Effects
Compressor Knee
The Knee parameter determines whether the signal is slightly, or severely, compressed as it
approaches the threshold level.
Setting a Knee value close to 0 (zero) results in no compression of signal levels that fall
just below the threshold, while levels at the threshold are compressed by the full Ratio
amount. This is known as hard knee compression, which can cause abrupt and often
unwanted transitions as the signal reaches the threshold.
Increasing the Knee parameter value increases the amount of compression as the
signal approaches the threshold, creating a smoother transition. This is called soft
knee compression.
Other Compressor parameters
As Compressor reduces levels, the overall volume at its output is typically lower than the
input signal. You can adjust the output level with the Make Up knob.
You can also use the Auto Gain parameter to compensate for the level reduction caused by
compression (choose either 0 dB or −12 dB).
When the Platinum Digital type is chosen, Compressor can analyze the signal using one of
two methods: Peak or root mean square (RMS). While Peak is technically more accurate,
RMS provides a better indication of how people perceive the signal loudness.
Note:
If you turn on Auto Gain and RMS simultaneously, the signal may become
oversaturated. If you hear any distortion, turn off Auto Gain and adjust the Make Up
knob until the distortion is inaudible.
Use a side chain with Compressor
Use of a side chain with a compressor is common. The dynamics (level changes) of another
channel strip is used as a control source for compression. For example, the dynamics of a
drum groove can be used to rhythmically change the compression, and therefore dynamics,
of a guitar, synthesizer, or bass part.
The side chain signal is used only as a detector or trigger in this situation. The side chain
source is used to control the compressor, but the audio of the side chain signal is not
actually routed through the compressor.
1. In Logic Pro, insert Compressor into a channel strip.
2. Click the Side Chain button in the Compressor window.
3. In the plug-in window header, choose the channel strip that carries the signal you want
to use as the side chain source from the Side Chain pop-up menu.
4. Choose the Max or Sum analysis method with the Detection buttons.
5. Adjust Compressor parameters.