Universal Audio Ampex ATR-102 Manual page 154

Output
Level (dB)
Figure 49. Input and output curve of compressor with 2:1 ratio and –20 dB threshold
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
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
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.
UAD Powered Plug-Ins Manual
Compression region
+10
0
–10
knee
–20
–30
–30 –20
Input Level (dB)
Figure 49, the input level is increased by 10 dB while the output
49.
2:1 compression ratio
–10 0 +10
- 154 -
10 dB of
compression
Chapter 15: LA-2A