Tuning down is extremely common today. In fact it’s almost a quaint curiosity when a band chooses to perform in standard tuning. But it wasn’t always this way. Once upon a time, almost everybody played in standard tuning (E A D G B E). But guitarists, like Indiana Jones and astronauts, are always striving for adventure and discovery, and this quest has led them to all sorts of lowered tunings. These tunings are of course distinct from the popular chord tunings (such as Open G) traditionally used in blues music, and generally their raison d’etre is to increase the heaviness of a riff.

Interestingly, one of the true pioneers of low tunings in metal – Black Sabbath’s Tony Iommi – played some pretty high chords in standard tunings earlier in his career. The first two Sabbath albums are full of standard tuning, and Iommi tended to play riffs on the lower two strings and higher up on the neck for a thicker sound. Some riffs like Iron Man even took Iommi up to the G5 power chord starting on the 15th fret of the E string. A few years later, however, the mighty Iommi was tuning all the way down to C# (C# F# B E G# C#) for songs like the still-crushingly-heavy-today “Sabbath Bloody Sabbath” from the 1973 album of the same name.

But Iommi’s early ’70s subsonic rumble was not the first popular lower tuning. Eb or “half-step down” (Eb Ab Db Gb Bb Eb) has been a very popular lowered tuning for decades. Jimi Hendrix was fond of it for much of his classic material. Other notable proponents include Stevie Ray Vaughan, Eddie Van Halen, Yngwie Malmsteen, Extreme’s Nuno Bettencourt and Alice in Chains’ Jerry Cantrell. It’s a popular choice for those who need to help a singer out a little bit because it’s still close to the guitar’s “regular” register but leaves a little headroom in case those high notes are just a little too high for the vocalist to comfortably reach. It also imparts a slightly darker tone thanks to the reduced string tension, although some players prefer to use heavier strings that can counteract this effect. Interestingly, the band Placebo commonly tunes up a half-step (F C G# Eb Bb F#).

Metallica’s “The Thing That Should Not Be” from Master of Puppets was a crucial example of a metal band pushing the tuning down for sonic effect rather than to placate a straining vocalist. That track is in C# Standard, and the band was fond of joking in contemporary interviews that the song was hard to play at outdoors venues because the strings would flap in the breeze. A few albums later Metallica explored D Standard for “Sad But True” and Eb on “The God That Failed.” By the time St. Anger rolled around they were delving fully into tunings like Dropped C (C G C F A D).

Drop D tuning (D A D G B E) practically deserves an article of its own, such is its influence and utility. This tuning is popular because it makes it possible to play power chords with a single finger barred across the lowest two strings. Players had experimented with this tuning for years before it became an integral part of the grunge movement – notable examples include Neil Young’s “Harvest Moon,” The Doors’ “The End,” The Beatles’ “Dear Prudence” and Fleetwood Mac’s “The Chain.” But Drop D really came into its own when applied to hard rock, heavy metal and grunge riffs. Although Led Zeppelin’s “Moby Dick” and “Ten Years Gone” are great early examples of a heavier band using the tuning, the critical turning point came with Van Halen’s “Unchained.” Eddie’s use of the tuning to play grinding repeated power chords in between higher chord stabs was as influential as it was innovative. Helmet’s Page Hamilton also helped to popularize it in a heavier setting. Now Drop D is almost the new standard, favored by acts like Muse, Evanescence, Rage Against the Machine, Radiohead, Avenged Sevenfold, Soundgarden, Foo Fighters, Incubus, Tool, Stone Temple Pilots and Nirvana.

But that aforementioned exploratory streak meant guitarists weren't happy to stay in Dropped D for too long. Drop C (C G C F A D), Drop C# (C# G# C# F# A# D#) and even Drop B (B F# B E G# C#) are incredibly popular today. Drop C users include Biffy Clyro, Bullet for My Valentine, System of a Down, P.O.D., Disturbed, Metallica (on St. Anger), and Staind. Drop C# advocates include Deftones, Evanescence (again), System of a Down (again), Trivium on their latest album In Waves, and Alter Bridge. Drop B is perhaps best known as “the Slipknot tuning” but is also employed by bands like Machine Head, Bring Me the Horizon and The Devil Wears Prada.

One increasingly popular tuning is Open C (C G C G C E), often used by Devin Townsend. A benefit of this tuning is that it creates extremely thick power chord sounds by simply barring one finger across the entire neck. Another is that if you fret the shape of a regular root-fifth-octave power chord you’re instead rewarded with a lush-sounding root-fifth-eleventh, a chord that can sometimes be a little tricky to fret in standard tuning, certainly in the middle of a fast riff. This tuning is also very shred-friendly as it allows you to create your own scales with interesting intervals that are easily repeated in different octaves. Below is an example of a six-note, pattern-based scale in the key of E – these types of scales are typically called “symmetrical scales” because they involve repeating a pattern across most of the neck. Usually they’re used to create atonal melodies, but Drop C is uniquely formulated to make them sound musical.