Pumping

A phenomenon associated with the use of dynamic processors such as noise reduction systems, compressors, and gates. Pumping is generally associated with breathing and is often used synonymously with that term. In context, the term pumping is also sometimes used to describe variations in the level of the desired signal that can occur as a result of the processor being unpredictably triggered by other elements of a sound that are not as apparent as the sound being processed. An example of this would be a wide band sound (like a full music track) where something that is happening in the very low end (perhaps below the frequency response of the studio monitors) is triggering the processor to make seemingly arbitrary (though often repetitive) changes to the level of the audio.