Jimi Hendrix was an American guitarist who, despite a brief, four-year professional career at the end of his life, is considered one of the most influential artists in the history of popular music. In the same way Bing Crosby forever changed popular singing, Hendrix employed the microphonic process to transform popular electric guitar performance practice. Of his many contributions, it was his use of feedback between his electric guitar and amplified loudspeaker that is most relevant to this discussion. Understanding the electric guitar, therefore, is the first step in examining his work. This description will draw from the fundamentals of sound, which I cover in Chapter 2.
The electric guitar is a hybrid acoustic-electric instrument whereby sound is first generated acoustically by the strings and then amplified electrically. The chain of sound generation is as follows: the strings are manipulated by the fingers or a plectrum (commonly known as a “pick”), and the strings’ vibrations are transformed to an electric signal by electromagnetic transducers (“pickups”). This electrical signal leaves the guitar by means of a cable, where it is sent to an amplifier and loudspeaker.1 The amplifier boosts the electrical signal, which then vibrates the loudspeaker’s diaphragm to finally transform the electrical signal into air pressure waves. The guitar that Jimi Hendrix most often used was a Fender Stratocaster. Much could be said about the design of the “Strat,” which is now an industry standard for electric guitars, but for the purposes of this discussion its basic components are all that need to be understood. 2 It has the customary six strings, a solid wood body, three pickups, a pickup selector switch, a volume knob, two tone knobs, a vibrato arm, and a ¼” output.
John Hanford analyzes the guitar virtuoso in his dissertation, “With the Power of Soul: Jimi Hendrix in the Band of Gypsys [sic].” The following summary communicates how profoundly innovative4 Hendrix was understood as:
Hendrix’s playing was staggering for both its originality and its full command of idiomatic expressions in rock, blues, and rhythm and blues. Most astonishing, though, was the array of new sounds coming out of his guitar; sounds that were overtly electronic and “futuristic” but primal in their affect. Weirdly beautiful, and sometimes of fearsome intensity, they passed by all understanding of conventional frames of reference for guitar playing.5
Like Crosby, Stockhausen, and Davies, Hendrix created these “futuristic but primal” sounds using an instrumentarium of media, expanding what the electric guitar was capable of. At the centre of this instrumentarium was the electric guitar and its components as listed above, which he manipulated through techniques uncommon to rock’n’roll at the time, such as tapping, plucking, and shaking. He also employed custom-made effects pedals to modify the electrical signal of his guitar, expanding his sonic palette. Most importantly, however, was how Hendrix exalted his amplifier6 to become an integral piece of his instrumentarium and therefore rock’n’roll guitar performance practice. He was, among other electric guitarists in the 1960s,7 famous for employing the “Marshall stack” in live performances. This amplified loudspeaker was designed in 1965 by British instrument manufacturer Marshall to have an imposing physical stage presence and to deliver incredibly high volumes.8 It is nearly 3’ wide and over 6’ tall, consisting of an amplifier on top of two stacked cabinets, each with four 12” loudspeakers inside. While performing at very high volumes was (and is) a common trait for rock guitarists, Hendrix was famous for his especially loud performances.9 The high volume he used not only provided an overwhelming experience for the audience but was technically functional in that it enabled his unconventional techniques to be clearly heard.10 In addition to its imposing stage presence, the amplifier’s size meant that much of its output could be directed towards the body of the guitar itself. This facilitated its most instrumental use in performance: acoustic feedback.
Guitarists necessarily divide acoustic feedback into two categories, “microphonic feedback,” also sometimes referred to as microphony; and simply “feedback,” which is occasionally called harmonic feedback. I use the terms microphonic feedback and harmonic feedback to distinguish between the two.11 While both forms of feedback adhere to the principles I outlined earlier, that of resonant frequencies being cyclically reinforced, the difference between them lies in whether the pickups or the guitar strings are the medium of reinforcement. In microphonic feedback, the wires in a guitar pickup vibrate from the sound coming from the amplifier. These wires are not designed to vibrate at all, let alone at a set frequency, so when they are subjected to incredibly high volumes, they act like a microphone and reinforce any resonant frequency in the system. Like most other acoustic feedback tones, the pitch resulting from microphonic feedback is indeterminate and often high and loud. Guitar pickups are often treated with wax on the inside to prevent this from constantly happening at high volumes.
Harmonic feedback occurs when the sound from conventional guitar string manipulation is amplified at such an intensity that the sound from the amplifier vibrates the string in turn, sustaining the initial note at pitch. Depending on the positioning of the guitar relative to the amplifier, harmonic feedback can also vibrate strings at higher overtones not available through conventional playing, as well as cause sympathetic vibrations in other strings. This style of feedback is somewhat predictable as it is related to the strings of the guitar, but can be disrupted by a myriad of factors. Therefore, “a player must, if attempting to create and design these sounds in live performance, make instantaneous analyses of feedback potential and be able to improvise alternatives when [harmonic] feedback cannot be induced, or, similarly, control it where it might unexpectedly be generated.”12
Hendrix on stage ramming his guitar into a Marshall Stack amplifier while stagehands attempt to keep it upright. Albert Hall, 1969.13
Through masterfully navigating the high-volume relationships within his instrumentarium of electric guitar, effects pedals, and amplifier, Jimi Hendrix unlocked the sustaining capabilities of harmonic feedback, forever changing electric guitar playing. In this navigation, all guitarists are forced into an active relationship with their amplifier, transforming it into an instrument that both supports the sound of the guitar14 and produces acoustic feedback through explicit interaction. Much like Bing Crosby, whose use of the microphone was assimilated into popular singing, harmonic feedback is now a standard part of electric guitar performance practice and can be expected to be heard in nearly every rock’n’roll setting. In contrast, microphonic feedback avoids systemization due to its indeterminate nature. This unpredictable quality is nevertheless explored and exploited in numerous process compositions of the classical avant-garde, of which Davies’ Quintet is a seminal example.
From using feedback as a musical device, both Hendrix and Davies can be considered engaging with microphonic instrumentaria in which loudspeakers are employed in interactive ways that reveal their instrumental contributions to musical outcomes. Much like Crosby and Stockhausen, the adoption of Hendrix’s and Davies’ innovations mirror their positions within popular and avant-garde traditions. Through developing microphonic practices, Crosby and Hendrix changed the performance practice of their instruments in lasting, widespread ways, whereas Stockhausen and Davies created microphonic works that appear and sound novel to this day. Despite their differences, these four artists share a common legacy through the microphonic process, an understanding which is facilitated by equal consideration across genres. This perspective continues in my analysis of two saxophonists who divergently employ the microphonic process in the 21st century.