rather distinct. Guitars and digital effects While most electronic effects units for electric guitar use footswitches to turn an effect on and off, some guitar effects, such as wah, vibrato, and swell, use a variable treadle-style pedal control similar to a keyboard expression pedal. Historically, these have been built into dedicated pedals for each effect, but modern digital amplifiers and processors allow many different effects to be built into a single, small floor or rack mount unit. Special built-in or plug-in expression pedals can be used with these devices to allow control of multiple effects with a single expression pedal. Using the expression pedal, the musician can not only emulate dedicated effects such as wah, but also have real time control of almost any variable such as volume, tone, echo repeats, effect speed, and so on. Some guitar expression pedals include integrated toe switches similar to those for some electric organs. The switches provide even more control, allowing the musician to turn effects on and off, and switch between different amplifiers. Expression has been taking a detour from pedals with advances in technology making smaller and remote devices possible. Motion controlled expression devices also called inertial audio effects controllers perform the same function as an expression pedal but provided added dexterity, movement dynamics and features. Synthesizers Expression pedals are typically used to control a range of synthesizer functions and effects parameters in real time. The most common type of pedal contains a simple potentiometer, mechanically linked to the pedal mechanism and electrically connected to the synthesizer, most commonly with a 1/4" TRS plug. Such pedals either require a built-in analogue pedal input, or must be converted to MIDI or USB for use with software synthesizers running on computers, using one of the commercially available pedal interfaces. References Pipe organ components