One of my favorite musicians to study (and teach my students) is Jeff Beck. In my opinion Beck is one of the most skilled electric guitarists alive, and has well adapted the instrument to push its boundaries. Of his many “sealable techniques” that everyone can learn and incorporate into their own playing, the one I teach the most is his use of volume swells. Of course, Jeff Beck isn’t the only guitarist to have made this technique a signature part of his playing— but the vocality in which he is able to achieve due to the technique is somewhat unique. While vibrato from the fretting hand and minute pitch shifts from the tremolo bar are fundamental to this vocality, the manipulation of the instrument volume is easily enough mimicked and learned.
With a Stratocaster style body shape (or any body shape where the guitar volume knob can be reached with the fourth finger while playing) manipulating the volume is less difficult. That said, the use of an in line volume pedal is more accurate. Either way, the same thing is happening. Lowering the output sends less signal out to the amplification device (either an amp, or some kind of DAW). This smooth analog and ergonomic motion allows for smooth gradations in dynamics. If a note or chord is fretted (ideally with some vibrato) while the instrument is muted, the slow increase in output can create a sonic effect that closely resembles that of a violin or cello. This stylistic aesthetic can be further pronounced by increasing the rate of volume acceleration with the frequency of pitch bend during a vibrato—i.e. The closer you get to maximum volume with your knob/pedal, the shorter and faster your vibrato should be.
If this isn’t something you’ve tried out before, give it a shot. Instead of starting at 0% volume/output and increasing it to 100%, try minimizing your parameters to 20-90% or “2” to “9” on your volume knob. This will allow you more control by necessitating less over all movement. With your fretting hand, try sliding up to the desired pitch along with using some vibrato… and remember to start “playing” before you begin increasing the volume. If you’re getting used to it, and want more control than a knob offers I’d recommend using a “Volume Pedal”. The Ernie Ball VP Jr. Is a simple and inexpensive favorite of many guitarists and bassists— on the other end of the spectrum, Dunlop’s “Steel Band Motion” of their own volume pedals offer incredible smoothness, adjustable tension, and superior signal quality (but are a tad expensive).
If you’re looking for some Jeff Beck examples of this technique I’d highly recommend searching YouTube for his performances of “Cause We’ve Ended As Lovers” and “A Day in the Life” from his show at Ronnie Scotts.