Boost/volume pedal: A boost or "clean boost" pedal amplifies the volume of an instrument by increasing the amplitude of its audio signal. These units are generally used for "boosting" volume during solos and preventing signal loss in long "effects chains". A guitarist switching from rhythm guitar to lead guitar for a guitar solo may use a boost to increase the volume of their solo.
Treadle-based volume pedals are used by electric instrument players (guitar, bass, keyboards) to adjust the volume of their instrument with one foot while their hands are being used to play their instrument. Treadle-style volume pedals are often also used to create swelling effects by removing the attack of a note or chord, as popularised by pedal steel guitar players. This enables electric guitar and pedal steel players to imitate the soft swelling sound that an orchestra string section can produce, in which a note or chord starts very softly and then grows in volume. Treadle-based volume pedals do not usually have batteries or require external power.