User Manual

UAD Powered Plug-Ins Manual - 116 - LA-2A and 1176LN
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 41) 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.
As mentioned previously, the compression ratio is defined as the ratio of the
increase of the level of the input signal to the increase in the level of the output
signal. In Figure 41, the input level is increased by 10 dB while the output
level increases 5 dB. This is a compression ratio of 2:1. Lower compression
ratios such as 2:1 result in mild compression. A compression ratio of 1:1
yields no compression.
Note: Compression ratios above 10:1 are commonly referred to as “limit-
ing” or “peak-limiting,” where amplitude peaks are reduced.
Compressors often let you set a threshold, the point at which gain reduction
starts to take place. When the level of an audio signal is below this threshold
there is no gain reduction. As the level of the signal increases above the
threshold level, gain reduction and compression occurs. The point at which a
signal transitions into compression is commonly referred to as the knee. In
practical compressors, this transition is more gentle than what is depicted in
Figure 41.
Figure 41. Input and output curve of compressor with 2:1 ratio and –20 dB threshold
–20
–10
0
+10
+10
–30
–10
–30 –20 0
2:1 compression ratio
10 dB of
compression
Compression region
Output
Level (dB)
Input Level (dB)
knee