Compressors and limiters are devices used to control the dynamic range of an audio signal. Compression can be used subtly and transparently or as effect, where the signal sounds completely “crushed”. Most of today’s modern rock and pop recordings use a lot of compression, both on individual instruments and the final mix. More compression is usually applied in the mastering process, often to make the mix sound loud and “in your face”. In classical and traditional jazz recording, compression is used much more subtly, if at all.
Compressors work by reducing the gain of an incoming signal by a user specified compression ratio. The processing is caused when the level of the signal exceeds a user specified threshold. Common ratios range from 2:1 to 16:1. Higher ratios of 20:1 or more are known as limiting because the gain reduction begins to take effect more suddenly after the threshold is exceeded. This can be useful for protecting amplifiers, speakers, and radio signal modulators from overloading. Most engineers favor recording with a small amount of compression in order to get more signal to the recording device