The FV500H from Boss is a both a volume pedal and an expression pedal for use with guitars and basses. When the pedal is plugged in between a guitar and an amplifier (or an input on a recording device), rocking the pedal back and forth will raise and lower the volume of the guitar. If you have an amplifier or an effect that can be controlled by an expression pedal, the FV500H has an output that enables it to be used as an expression pedal.
The construction of the FV500H is very strong. It was built to be stepped on over and over again. It features rubber grips that help to keep your feet from slipping off, and make for a more comfortable playing experience. You can even adjust the torque of the FV500H to your liking. It features high-impedance inputs and outputs that make it ideal for use with guitars and basses. A third output is provided to connect the FV500H directly to a guitar tuner.