Apple Logic Express 7 - Manual (Page 29)

Chapter 4 Dynamic 29
When you have configured a compressor so that it dampens the signal at or above the
Threshold value by the predetermined Ratio, while the level just below the Threshold is
routed through at a 1:1 Ratio, an audio engineer would term the compression as hard
knee. In many cases, however, you’ll come up with a better sounding track by using a
more gradual transition from the 1:1 Ratio below the Threshold, to the Ratio that you
entered for levels above the Threshold. In this scenario, the characteristic curve is not as
radical—it rises gradually from the bottom left to the top right, as seen in the graphic
display. This type of compression is called soft knee. The Knee slider lets you
incrementally select anything from hard to soft knee. This wide range of options
provides you with the tools you need to shape the sound as you like; whether you
want to radically maximize loudness with absolutely no regard for the original
dynamics (hard), or are going for the more musical compression that acoustic
recordings typically require (soft). Keep in mind that Knee only controls the shape of
the compression, not its intensity; use the Threshold and Ratio sliders for this purpose.
Incidentally, the Gain Reduction Meter indicates the intensity of compression used to
tighten up the original signal. This feature is a great help, particularly if you’re not
experienced with using compression. Keep an eye on it to make sure that you’re not
overly compressing your tracks.
When the compressor has to decide whether or not the level exceeds the Threshold (or
if the level is getting close to the Threshold, for soft knee compression), it can analyze
either the peak or RMS level. The latter value is a better indication of how humans
perceive loudness. When you use the compressor primarily as a limiter, select the Peak
button. When you’re compressing individual signals, use of the RMS button will often
deliver better, more musical results.
If you activate Auto Gain and RMS simultaneously, the signal may be saturated. If you
hear any distortion, switch Auto Gain off, and enter a suitable gain level manually.
The Output Clip parameter limits (clips) the output to 0 dB, via the OFF/SOFT/HARD
settings. This setting is only available if the 001/011 button is activated.
Note: Despite all of these handy tips for tweaking sounds, you should always keep one
thing in mind—there are no hard and fast rules. Use your own taste and ears. If it
sounds good, it is good.