Effects units are electronic devices that alter how a musical instrument or other audio source sounds. Some effects subtly "color" a sound, while others transform it dramatically. Effects are used during live performances or in the studio, typically with electric guitar, keyboard and bass. While most frequently used with electric or electronic instruments, effects can also be used with acoustic instruments, drums and vocals. Examples of common effects units include wah-wah pedals, fuzzboxes and reverb units.