A clipper is a type of audio signal processing unit that is used to remove the very slightest amount of extremely high or low frequencies from an audio signal. The amount of change that a clipper makes to the sound is usually so subtle that it's barely noticeable, which is why this type of processor is often used on guitars, kick drums, and vocals. Compressors are also types of audio signal processing units, but their purpose is very different from that of a clipper. Whereas a clipper works to remove extremely high or low frequencies, compressors work to even out the levels of an audio signal by reducing the dynamic range (the difference between the loudest and softest parts). Compressors can be used to make a track sound fuller and more polished, or they can be used to create special effects such as "pumping" and "breathing."