Compression pedals are one of the most subtle - and perhaps most misunderstood - of all pedal effects. What a compressor does is decrease the volume of louder notes and increase the volume of softer notes, thus making the sound volume more consistent. The effect gives the guitar a more percussive sound and can also be used to increase sustain. Originally, compressors were fairly noisy and had to be combined with noise gates; however, modern units are far less susceptible to noise and offer excellent sound-noise performance. Andy Summers and David Gilmour are two prominent users of the compressor, as are most studio guitarists.