Compressor

The compressor sound effect limits the volume levels of a sound recording so that it stays within a certain loudness range. An example of where it is used is in TV broadcasting, where it ensures that the volume levels of ads are perceived as being louder than the television program itself, without any change in the actual broadcast volume.

It also has a use for recording audio from one medium to another, where the two mediums are not capable of handling the same range of volume levels (e.g., A CD can handle a much greater range than a cassette tape).

The "Threshold" setting works by detecting when the sound recording volume exceeds a defined decibel level. It then gradually attenuates the sound to bring it down below the dB level, and does it in such a way that the listener will not be aware the attenuation is occurring.


The "Ratio" setting limits the amount the volume level of the recording increases at any one time. If, for example, you wanted the volume levels of a recording to only increase by at most 1/4 of the amount they would normally increase, then this would correspond to a Ratio of 4:1. So if the recording volume level increased by 8dB, then you would only hear a 2dB volume increase.


The "Limit" setting defines at what maximum decibel level the sound recording will be allowed to rise up to. So if, for example, the Limit was set to 0dB, then you will never hear the volume level of the recording get louder than 0dB. The Limit setting has similarities to the Threshold setting, but the main difference is that the Threshold does allow sounds to go above the defined decibel level (for a short time), whereas the Limit does not.


You will find that the minimum Limit volume you can set is the same as the maximum Threshold value. This basically means that, in any situation, the sound will start to attenuate at the threshold level, but will never be heard louder than the limit.