User Manual

UAD Powered Plug-Ins Manual - 110 - Chapter 11: LA-2A and 1176LN
Figure 26 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 26, 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 26, 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).
The amount of compression, or gain reduction, typically expressed
in decibels (dB), is defined as the amount by which the signal level is reduced
by the compressor. Graphically, this can be represented (see Figure 27) by
the difference in output levels between the original signal (without compres-
sion) and the compressed signal. The LA-2A and 1176LN display this value
when their VU Meters are set to Gain Reduction.
Figure 26. 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)