10
Limiting versus compression
A compressor typically has a compression ratio lower than 10:1. A limiter has a compression
ratio higher than 10:1. For example, with a ratio of 4:1, an input level increase of 4 dB will only
result in a 1 dB output level increase.
The threshold is the level the input signal must reach before compression begins. Gain
reduction is only applied to audio that exceeds the threshold.
When an audio signal is below this threshold the compressor acts like an amplifier and there is
no gain reduction. Above the threshold, the slope becomes less than 45 degrees, indicating
gain reduction and hence compression. The point at which a compressor transitions into
compression is commonly called the knee.
Figure 2.
Compression/limiting curves.
Compression is suitable for leveling and reducing the general dynamic range of individual
instrument tracks such as vocals and drums.
Limiting is used to limit the dynamic range and increasing the perceived overall level of the mix,
and to prevent the audio signal from exceeding a specific level.
Note:
The CA-2A T-Type Leveling Amplifier compression ratio is frequency-dependent. In
Limit mode, the compression ratio can go as low as 4:1 for low frequencies.
Limit curve (4:1 to 20:1)
Compress curve (3.5:1 to 6:1)
Threshold
Input level
Output
level
No gain reduction
Gain reduction amount
Knee
