The category encompasses devices that modulate the volume of an audio signal to create a pulsating or rhythmic effect. Functionally, this results in a wavering sound, simulating a tremulous, shaking quality applied to the notes produced by a guitar. Early examples were often built into amplifiers, while modern implementations exist primarily as standalone effects units that can be integrated into a signal chain.
The effect provides a distinctive character to guitar tones, lending itself to various genres, including surf rock, blues, and indie music. Its usage can add depth and movement to chords, single-note lines, and overall sonic textures, serving as a tool for subtle enhancement or dramatic rhythmic alterations. The origin of the effect can be traced back to early amplifier designs, with its evolution reflecting advancements in electronics and sound manipulation technologies.
