chord" (three-note fifth) with the low three strings (DAD). There also exists double-drop D tuning, in which both E strings are down-tuned a whole step (to D). The rest of the strings keep their original pitch. Although the drop D tuning was introduced and developed by blues and classical guitarists, it is well known from its usage in contemporary heavy metal and hard rock bands. Early hard rock songs tuned in drop D include The Beatles' "I Want You (She's So Heavy)" and Led Zeppelin's "Moby Dick", both first released in 1969. Tuning the lowest string one tone down, from E to D, allowed these musicians to acquire a heavier and darker sound than in standard tuning. Without needing to tune all strings (Standard D tuning), they could tune just one, in order to lower the key. Drop D is also a convenient tuning, because it expands the scale of an instrument by two semitones: D and D. In the mid 1980s, three alternative rock bands, King's X, Soundgarden and Melvins, influenced by Led Zeppelin and Black Sabbath, made extensive use of drop D tuning. While playing power chords (a chord that includes the prime, fifth and octave) in standard tuning requires a player to use two or three fingers, drop D tuning needs just one, similar in technique to playing barre chords. It allowed them to use different methods of articulating power chords (legato for example) and more importantly, it allowed guitarists to change chords faster. This new technique of playing power chords introduced by these early grunge bands was a great influence on many artists, such as Rage Against the Machine and Tool. The same drop D tuning then became common practice among alternative metal acts such as the band Helmet, who used the tuning a great deal throughout their career and would later influence much alternative metal and nu metal bands. Open tunings An open tuning allows the guitarist to play a chord by strumming the open strings (no strings fretted). Open tunings may be chordal or modal. In chordal open tunings, the open chord consists of at least three different pitch classes. In a given key, these are the root note, its 3rd and its 5th, and may include all the strings or a subset. The tuning is named for the base chord when played open, typically a major chord, and all similar chords in the