It’s now 20 years since the grunge revolution changed the course of mainstream music and made the term “alternative” into a buzzword (and a category on record store shelves). Arriving in the wake of a particularly technical epoch – both in terms of gear and guitar playing – grunge redefined what a guitar tone could be, and did away with the more histrionic guitar vocabulary developed during the preceding decade. Grunge may not have had an Eddie Van Halen or an Yngwie Malmsteen in terms of technique and instrumental excess, but the genre was never short of guitar innovators.

Of course, the roots of grunge began far before the ’90s, and elements of the style can be heard as far back as the early ’70s – or maybe even the late ’60s garage band scene. David Bowie’s album The Man Who Sold the World reads as a virtual blueprint of grunge 20 years before the fact, with its colossal ringing chords, mournful melodies and lonesome single-note lines. Its title track was famously covered by Nirvana, while “Width of a Circle” and “All the Madmen” also offered strong hints as to the direction popular music would take two decades later. Bowie guitarist Mick Ronson’s lead lines were more modal in nature than the predominantly blues-derived soloing of mainstream hard rock, another trait later exhibited by ’90s grunge guitarists.

The classic grunge guitar tone was typically achieved via a combination of tube amps and distortion or fuzz pedals rather than pure amplifier distortion alone, and was usually characterized by a thick midrange, somewhat dulled treble edge and a relatively narrow dynamic range (naturally, there were a few exceptions). Great grunge tones tended to support the heaviness of the downtuned, downtempo riffage that characterized the style, so thin, buzzsaw-like tones were scarce on the ground unless used for a specific effect. Many guitarists of the era preferred to generate their tone via the use of ’70s fuzz boxes into clean amps, and a popular trick involved stringing several dirt boxes together. The Smashing Pumpkins’ Billy Corgan was a notable exception, using several types of rack-mounted preamps.

While many of grunge’s most iconic tones came from standard off-the-shelf guitar gear, some other tones were from decidedly less conventional setups. Kurt Cobain notoriously used a power amp designed for driving a PA system to get his early tone – in fact, he used four of these particular 800-watt behemoths – fed by a more conventional studio guitar preamp, although these particular power amps were rather frowned upon by Cobain's tech, and were eventually replaced by more reliable models.

In a similar but likely more tech-pleasing way, Soundgarden’s Kim Thayil favored a bass combo amp with a 15-inch speaker in the band’s early days, which was perfectly suited to handling the impact of his downtuned riffs and making sure his playing could be heard, as most guitar amps of the era were not designed to project the kinds of low tunings preferred by grunge players.

Grunge players tended to get by with a bare minimum of other effects that were almost always in the form of analog pedals rather than digital rack units. In fact, the grunge era’s predilection for pedals was largely responsible for the shift away from rack effects and towards boutique stompers in the ’90s. Many grunge guitarists, particularly Thayil and Alice in Chains’ Jerry Cantrell, were great advocates of the wah wah pedal, and both guitarists could often be heard either leaving the pedal in a stationary position as a tone enhancer or hovering it around a specific frequency, Zappa-style. Thayil can be heard using the wah as a tone enhancer on “Rusty Cage” while Cantrell uses the hover and emphasize method on the title track from the Dirt album.

One cannot discuss grunge guitar without talking about the iconic grunge tuning. While blues players had experimented with dropping the E string to D for decades, and even Eddie Van Halen had done so on tracks like “Mean Streets,” grunge players really made the tuning their own. Aside from making it easier to play power chords by needing only one finger, the lowered tuning was also more in sync with the darker, moodier atmosphere of the style in general – not to mention the deeper vocal style preferred by the majority of grunge vocalists. Drop D also provided for some interesting extended chords and arpeggios beyond the simple two-note power chord form.

It’s kind of hard to grasp how much of an impact Drop D had on guitar playing. Again, some bands had experimented with lower tunings and Steve Vai was going all the way down to B with his seven-string guitars, but if a guitarist in the ’60s, ’70s or ’80s tuned down at all, it was usually to E flat.

Although grunge burned brightly in the early ’90s and fizzled out quickly around the middle of the decade, its legacy on guitar will forever be heard whenever anyone tunes down lower than E Standard. And some music industry pundits are pointing to signs of an imminent grunge revival in the hands of bands like The Joy Formidable, Mr. Dream and Yuck.