TDM Audio 32CL-2 v.2 - Manual (Page 6)

© 1996 TDM Design, Inc. Compressor/Limiter Owner’s Manual Page 6
If all of this math confuses you, you are not alone. You don’t need to thoroughly understand it to
work with compressors, though. It is presented so that you have the background necessary to
understand how compressors work. Normally, you set the compression ratio based on how severe
you want the compression (or gain reduction) to be, and you set the threshold to where you want
the compression to begin. Ratios are usually set to a ballpark value based on the kind of sounds
being compressed, and thresholds are generally fine-tuned to achieve exactly the desired affect.
Limiter Fundamentals
A limiter is really just a compressor with a really high compression ratio. One of the main real-
world differences between a limiter and a compressor is that a limiter is a hard-knee device. The
knee here is the knee of the curve that graphs input level vs. output level. Compressors tend to be
soft-knee devices. A compressor eases across the threshold gently and then begins compressing
the signal at the specified ratio. A limiter hits the threshold like a brick wall and then refuses to let
the level go any higher. Limiters are used to set an absolute maximum level and then guarantee
that the level will not pass it. A limiter has a ratio nearing infinity to one.
While compressors are often used to enhance sound quality, limiters are used mostly for protec-
tion purposes. A radio station might use a nice 4:1 compression ratio to even out the sound of the
announcer’s voice, but a limiter might be set to make sure that no matter what happens, the level
doesn’t go over the maximum modulation level allowed by law. Here the limiter is a protection
mechanism. Limiters are used in large concert sound systems to prevent damage to speakers (and
ears).
Limiters are much easier to use than compressors. It is not necessary to understand how the
output level, compression ratio, and threshold interact to produce a certain effect. A limiter is
used by simply setting the absolute maximum level as the threshold.