18V refers to a type of power supply used by certain guitar pedals to provide higher voltage than the more common 9V pedals. Using 18V power can result in greater headroom, improved dynamics, and more detailed tonal response compared to a 9V power supply. Many high-performance pedals, such as certain overdrive, distortion, and delay units, are designed to operate at 18V to deliver enhanced sound quality, allowing for greater clarity and less distortion at higher volumes.

Pedals that run on 18V, like the MXR Phase 90 (with an 18V option) or the TC Electronic Flashback Delay, often produce a fuller, more robust sound, with increased sustain and more natural tonal characteristics. Musicians may choose 18V-powered pedals for their ability to offer a more open sound, particularly in high-gain settings, where 9V pedals might start to compress or become muddier.