User manual

UAD Powered Plug-Ins Manual - 120 - LA-2A and 1176LN
Compressor Basics
Before discussing the LA-2A and 1176LN plugins, this section will cover some
compressor basics. A compressor automatically adjusts the gain of a signal
by a predetermined ratio. In a sense, a compressor “rides” gain—much like
a recording engineer does (by hand) with a fader—keeping the volume up
during softer sections and bringing it down when the signal gets louder.
Figure 41 depicts the input and output characteristics of a compressor and
perfect amplifier. When operated within its specified range, an amplifier pro-
vides a constant amount of gain regardless of the input signal level. In
Figure 41, the signal level of a perfect amplifier is represented with a constant
output gain of 10 dB. In this example, a signal with an input level of –30 dB
results in an output level of –20 dB, which is an increase of 10 dB. Similarly,
an input level of 0 dB results in an output level of 10 dB (the gain stays fixed
at 10 dB regardless of the input level).
In contrast to an amplifier, whose function is to present a constant gain, a
compressor varies its gain in response to the level of the input signal. Large in-
put signals result in less gain, thus reducing or compressing the dynamic
range of the signal. In Figure 41, a compressed signal with an input level of
–30 dB results in an output level of –20 dB, indicating a gain of 10 dB. How-
ever, with input levels of –20 dB and –10 dB, the compressor exhibits gains
of 5 dB and 0 dB (respectively), thereby illustrating that the gain decreases as
the input signal increases. This increase in output level by 5 db for every
10 dB is defined as a compression ratio of 2:1 (reduced from 10:5).
Figure 41. Input and output characteristics of a compressor and perfect amplifier
–20
–10
0
+10
+10
–30
–10
–30 –20 0
Perfect
Amplifier
Compression
Output
Level (dB)
Input Level (dB)