Dropped tunings (or drop tunings) are a family of guitar tunings in which the sixth string is tuned one whole step lower in relation to the other strings than in standard tuning. Dropped D is so called because the low E string in Standard tuning is tuned down ("dropped") by two semitones to D. Other tunings can then be achieved by downtuning the guitar as a whole, and are generally referred to as drop[ped] n (where n is the pitch to which the sixth string is tuned).
A D5 power chord played in Drop D tuning
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In dropped tunings the three bass strings form a power chord, which can be shifted up or down the fretboard with a single finger to produce any power chord. Dropped tunings are frequently used in heavy metal, as guitarists in that style often need extremely fast transitions between power chords. However, the tuning has also been used in many other types of music, including blues, country, folk, and classical.
Drop D also allows fingerpickers to play chord shapes higher up the neck while maintaining an alternating bass. The tuning also allows for chords with a root or bass note of D to be played with a D an octave lower than with standard tuning, and allows playing of open D chords to include the fifth and sixth strings for a fuller sound. This can be especially useful for songs in the keys of D major or minor. The tradeoff is the loss of the bass E note in chords or fingerings which the player cannot adjust to include fretting the sixth string at the second fret.
Drop D♭ Tuning, also referred to as Drop C♯ Tuning, is an alternative guitar tuning. It is similar to Drop-D tuning, having the lowest (sixth) string dropped down three semitones to Db, with the rest of the strings being tuned down one semitone. The tuning (from low strings to high strings) is D♭ A♭ D♭ G♭ B♭ E♭. This type of tuning is mostly used by modern rock bands such as Alter Bridge, as on their first album, One Day Remains, Linkin Park on their first and second album, and the Japanese rock band Dir en grey. Billy Corgan of the Smashing Pumpkins popularized this tuning on albums such as Mellon Collie and the Infinite Sadness, where he referred to it as 'grunge tuning'. Daron Malakian of System of a Down also used this tuning in System's double album, Mezmerize/Hypnotize. Aiji, of LM.C uses this tuning in the most of the songs of the band. A few of Protest the Hero's songs off of the album Kezia are in this tuning as well. Fireflight uses Drop-D♭ in all of their songs.
Drop C tuning is a type of guitar tuning. Though there are variations, the most commonly intended spelling of Drop C is CGCFAD. This can be described as "standard D tuning with a dropped C", or "drop D tuning transposed down a whole step", where the entire guitar is transposed to the key of D, then the low D is moved down an additional whole step to C. For usage and benefits, see Drop D tuning.
Bands or artists that use or have used this tuning include:
- 16 Volt
- A Day To Remember
- Alter Bridge (two songs on their first record)
- Aretha Franklin ("Chain of Fools")
- Atreyu
- As I Lay Dying
- August Burns Red
- Avenged Sevenfold
- Bayside
- Berri Txarrak (some songs)
- Biffy Clyro
- Black Dahlia Murder
- Black Label Society
- Born of Osiris
- Boys Like Girls
- Breaking Benjamin
- Bullet For My Valentine
- Children Of Bodom (some songs)
- Chimaira 
- Disturbed
- Hanzel Und Gretyl
- I Killed The Prom Queen
- Killswitch Engage
- Kittie
- KMFDM
- Linkin Park
- Lost Prophets(Shinobi vs Dragon ninja)
- Metallica (on the album: St Anger)
- Nickelback
- P.O.D. (They also use D standard)
- Porcupine Tree (on the album: Fear of a blank planet)
- Queens Of The Stone Age (but they sometimes tune all strings two steps down from standard)
- Rammstein
- Red Jumpsuit Apparatus
- Rob Zombie
- Saosin
- Sentenced
- Shadows Fall
- Sick Puppies
- Sigma
- Skillet (Monster)
- Slipknot (some songs)
- Steve Vai
- Stone Sour
- System Of A Down
- The Faceless
- The 69 Eyes
- There For Tomorrow (Ice Box) 
- Three Days Grace
- Warrel Dane
- Bring Me The Horizon
A Dropped B tuning is a alternate tuning for a guitar where the strings are tuned to B-F♯-B-E-G♯-C♯ (top to bottom, or lowest sounding strings to the highest sounding strings).
You can achieve a 'Dropped B' tuning by de-tuning the bottom 5 strings (the highest sounding strings) down a minor third (a tone and a half, or 3 frets) from the standard 440Hz 'A' tuning (the default tuning for most tuners). The top string (lowest sounding string) is detuned down a perfect fourth (two and a half tones or 5 frets).
This tuning allows the guitarist to anchor the harmony with basic root chords (sometimes called 'power chords', i.e. 1st, 5th and octave) with one finger, while freeing up the other 3 fingers to play melodies or add to the harmony.
The de-tuning of the strings may cause the strings to rattle against the fretboard; due to that, heavy gauge strings are highly recommended. However, this rattling sound can be hidden by using a distortion effect. As a result it is a tuning more commonly used in metal music than other types of music. First pioneered by Sepultura this tuning has been used by bands such as:
- Bring Me The Horizon
- Electric Wizard
- Machine Head
- Parkway Drive
- Stone Sour
- The Kills
- Demon Hunter
B♭, said as "B-flat", is the half step in between B tuning and A tuning. Drop B♭ tuning can be achieved on a six-string guitar by dropping the strings, from low to high, B♭-F-B♭-E♭-G-C (or A♯-F-A♯-D♯-G-C) or on a 7 string guitar, B♭ F B♭ E♭ F♭ C F (A# F A# D# G# C F) . This tuning can be utilized in another version, known as B♭ tuning, in which the strings are tuned B♭-E♭-A♭-D♭-G♭-B♭ (or A♯-D♯-G♯-C♯-F♯-A♯). In Flames, Emmure, Celtic Frost(at least on the Monotheist album),Chevelle, Benea Reach, and Breaking Benjamin have all used this tuning.
Dropped A is an alternate tuning for a guitar where the strings are tuned to AEADF♯B. It has been used by Buzz Osborne of The Melvins, Karl Sanders of Nile, Jim Root and Mick Thomson of Slipknot, and in recent years primarily by deathcore bands, such as Suicide Silence.
Seven stringed guitars
It is possible to drop-tune a seven-string guitar, and achieve the same ease of power-chording as in dropped six-string tunings. At least two variants are known - AEADGBE, in which the guitar is tuned like a six-stringed guitar in standard, but with an added low A, and AEADF#BE, in which the guitar is tuned as in dropped A (see above), but with a high E string.
- Bienstock, Richard (2001). "Knot Again!: Slipknot, A Dark Punishing Wind Blowing from the Bowels of the Midwest". Guitar World. Hal Leonard Corporation: 19–26. Unknown parameter