A volume swell is a musicalcrescendo commonly associated with the electric guitar. It is achieved by cutting the initial attack of the note, either with the volume potentiometer on the guitar or with a volume pedal.
Principle
Roughly speaking, the sound of a guitar note is characterized by an initial 'attack' where the pick or finger produces higher pitched overtones over the top of the fundamental note, followed by a diminution of these overtones. Consequently, the end of the note is softer than the attack. Volume swells alter the tone of the note, reducing the treble tones of the attack and allowing the softer tone that follows to sustain.
The technique is often executed using the guitar's volume knob. Beginning with the knob turned down to zero, it is increased when a note is played. The effect can also be performed by using a volume pedal. It is sometimes called "violining", because the sound is similar to a bowed violin.[1] Volume swells can be used in conjunction to bending in order to make it sound like a human voice raising in pitch and volume.[2]
Allan Holdsworth pioneered the technique of the pedal swelling along with a delay unit to create a thicker sound that is more associated with the cello.
Notable users
Jeff Beck used volume swells throughout his career, an example being "Where Were You" from his 1989 album Jeff Beck's Guitar Shop.