TDM Audio 32CL-2 v.2 - Manual (Page 13)

© 1996 TDM Design, Inc. Compressor/Limiter Owner’s Manual Page 13
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Limiter Threshold: This knob sets the threshold of limiting. The threshold of limiting is the
absolute maximum level that you ever want at the output of the compressor/limiter. For more
information about limiter thresholds, see Limiter Fundamentals. The limiter threshold can be
varied from -40 dBm to +20 dBm, and is an absolute maximum— it is not affected by the out-
put level control. This means that the limiter threshold stays the same as the output level is
varied. Another way to look at this is that the limiter threshold is an output threshold. Limiting
begins when the output level reaches the threshold. The compressor threshold is an input
threshold so compression begins when the input reaches the threshold.
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Signal Light: This light comes on when signal is present at the input of the channel.
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Peak Light: This light comes on when the output level reaches its peak. If the output signal is
greater than the peak, audible distortion can result. It is okay if this light occasionally flashes,
but if it flashes a lot or stays on consistently, reduce the output level by turning down the out-
put level control, and find a way to get more gain out of some other component in the system
that is after the compressor/limiter. For example, if you are compressing a live mix you might
want to turn down the output level of the compressor/limiter and turn up the gain on the
power amplifiers or on the crossover.
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Compression Light: This light comes on when the input level is over the compressor thresh-
old. It indicates that compression is taking place.
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Limit Light: This light comes on when the output level is over the limiter threshold. It indi-
cates that limiting is taking place.
Basic Compressing
This section will give inexperienced users the basic information they need to use the compressor.
If you are new to compressors, expect a lot of trial and error to find the best settings for your
particular needs.
The objective when compressing a signal is to get its dynamic range to the desired place. Most
often, signals that need compression are just signals whose level varies too much and you want to
reduce the dynamic range to something usable. Another way to look at this is that a signal needs
compressing if when you turn it up so you can hear the quietest parts, the loudest parts are too
loud.
Start with the output level at 0 (straight up), the threshold at 20 (fully clockwise), and the ratio at
1:1. This setting just passes the signal through with no compression. Start with the attack and
release both in (fast), and make sure the limiter threshold is at 20 (fully clockwise) for no limiting.
Begin with some idea of the kind of compression ratio you need. For more information on com-
pression ratios, see Compressor Fundamentals. Remember that you will generally not compress
the quiet parts of the signal very much, only the louder parts. If your compression ratio is too low,
your threshold will need to be set too low to achieve the correct amount of gain reduction. This
will result in breathing and other undesirable side effects. If your compression ratio is too high,
only the very loudest parts of the signal will be compressed, and they will be compressed severely.
This will sound unnatural. It takes time and experimentation to fully understand all of the trade-
offs involved so an intelligent choice can be made. The basic rule of thumb is that the less com-
pression you expect to need, the lower the ratio you should use. Use the lowest possible ratio and