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UAD Powered Plug-Ins Manual - 283 - Chapter 25: LA-2A and 1176LN
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 92
, 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:
C
ompression 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 92
.
Most modern compressors provide a control that adjusts the threshold di-
rectly. In the case of the LA-2A, the Peak Reduction control adjusts both the
threshold and the amount of gain reduction. Similarly, the 1176LN uses its In-
put control to adjust the threshold and amount of gain reduction.
Figure 92. 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