TDM Audio 32CL-2 v.2 - Manual (Page 15)

© 1996 TDM Design, Inc. Compressor/Limiter Owner’s Manual Page 15
a program to be compressed, but when a boisterous speaker takes the microphone, the entire time
he or she is speaking, he or she is in compression. The common way to deal with this problem is
by using a slow release rate.
Slow release rates are used for applications where the input level remains fairly constant for a long
period of time at one level, and then remains fairly constant for a long period of time at another
level. You need compression to even out the levels, but you don’t want the compressor wildly
jumping around during a particular level. With a slow release rate, the compressor takes its time
letting the gain go back up when the speaker pauses. If the speaker starts right back in again, the
gain has not been increased significantly, so the sound is more natural.
One of the problems that can be caused by a slow release rate is the phenomenon of percussive
sounds “punching holes in the program.” If you are using a slow release rate, and the speaker
makes a particularly percussive “P” sound into the microphone, the resulting transient causes the
gain to be reduced substantially, and the gain takes quite a while to get back up to its previously
correct level. The effect is that of the “P” punching a hole in the program. The solution to this
problem is to use a slow attack rate. A slow attack rate causes the compressor to take more time
to reduce the gain in response to a loud sound. The sound has to be loud for a reasonable length
of time in order for the compressor to respond by reducing the gain. The result can be a more
natural sound, but it is only useful when the sound level stays fairly constant for long periods of
time. Slow attack and release rates form a sort of “gain inertia” where the gain has a healthy and
natural resistance to change. For some applications, such as speech, this can be very useful.
Compressing Vocals
Compressing a singer is similar to compressing a speaker, except that the dynamic range is gener-
ally much greater, and the input level is constantly changing. You would usually not want to use
slow attack and release rates with singers because the compressor would not react quickly enough
to be of much use. For singers with a lot of dynamic range, you can use compression ratios of up
to about 8:1 without sounding too unnatural. It is important that the threshold is not set too low
because the dynamic nuances of the quiet parts of the sound can be lost. One problem that setting
thresholds too low on vocalists can cause is an unnatural emphasis on sibilance and on breaths.
These problems are common even with tame compressor settings sometimes, so it is often advis-
able to use side chains to deal with them. For more information on how to do this, see the next
section Using Side Chains.
When compressing microphones used in live reinforcement, it is very important that the threshold
is not set too low. Thresholds that are set too low can cause feedback problems. If you are com-
pressing a vocalist, and you can’t seem to get enough gain during the loud parts of the music, do
not just keep pushing the fader up. If you do, when the music stops the microphone will probably
immediately begin to feed back. Instead, realize that the loudest needed signal has changed from
what you originally thought it was, and raise the compressor threshold until you get enough vol-
ume. Moving faders up and down constantly defeats the main purpose of compression— to
manage the dynamic range of the vocalist so you don’t have to.