thumb|350x350px|E5 power chord in eighth notes A power chord , also called a fifth chord, is a colloquial name for a chord (in the broader sense of two or more notes played simultaneously) on guitar, especially on electric guitar, that consists of the root note and the fifth, as well as possibly octaves of those notes. Power chords are commonly played with an amp with intentionally added distortion or overdrive effects. Power chords are a key element of many styles of rock, especially heavy metal and punk rock.
Analysis
When two or more notes are played through a distortion process that non-linearly transforms the audio signal, additional partials are generated at the sums and differences of the frequencies of the harmonics of those notes (intermodulation distortion). When a typical chord containing such intervals (for example, a major or minor chord) is played through distortion, the number of different frequencies generated, and the complex ratios between them, can make the resulting sound messy and indistinct. This effect is accentuated as most guitars are tuned based on equal temperament, with the result that minor thirds are narrower, and major thirds wider, than they would be in just intonation.
However, in a power chord, the ratio between the frequencies of the root and fifth are very close to the just interval 3:2. When played through distortion, the intermodulation leads to the production of partials closely related in frequency to the harmonics of the original two notes, producing a more coherent sound. The intermodulation makes the spectrum of the sound expand in both directions, and with enough distortion, a new fundamental frequency component appears an octave lower than the root note of the chord played without distortion, giving a richer, more bassy and more subjectively "powerful" sound than the undistorted signal. Even when played without distortion, the simple ratios between the harmonics in the notes of a power chord can give a stark and powerful sound, owing to the resultant tone (combination tone) effect. Power chords also have the advantage of being relatively easy to play , allowing fast chord changes and easy incorporation into melodies and riffs.
Terminology
thumb|In a triadic context, chords with omitted thirds may be considered "indeterminate" triads. |150x150px
Power chords are most commonly notated 5 or (no 3). For example, "C5" or "C(no 3)" refer to playing the root (C) and fifth (G). These can be inverted, so that the G is played below the C (making an interval of a fourth). They can also be played with octave doublings of the root or fifth note, which makes a sound that is subjectively higher pitched with less power in the low frequencies, but still retains the character of a power chord.
Another notation is ind, designating the chord as "indeterminate". Scotty Moore opened Elvis Presley's 1957 hit "Jailhouse Rock" with power chords. The "power chord" as known to modern electric guitarists was popularized first by Link Wray, who built on the distorted electric guitar sound of early records and by tearing the speaker cone in his 1958 instrumental "Rumble."
A later hit song built around power chords was "You Really Got Me" by the Kinks, released in 1964. This song's riffs exhibit fast power-chord changes. The Who's guitarist, Pete Townshend, performed power chords with a theatrical windmill-strum, for example in "My Generation". On King Crimson's Red album, Robert Fripp thrashed with power chords. Power chords are important in many forms of punk rock music, popularized in the genre by Ramones guitarist Johnny Ramone. Many punk guitarists used only power chords in their songs, most notably Billie Joe Armstrong and Doyle Wolfgang von Frankenstein.
Techniques
Power chords are often performed within a single octave, as this results in the closest matching of overtones. Octave doubling is sometimes done in power chords. Power chords are often pitched in a middle register.
Image:f5chords.png
Shown above are four examples of an F5 chord. The letter names above the chords only indicate which different voicing is being used, and should not be conflated with the chord names typically used in popular music (e.g., C Major, B minor, etc.) A common voicing is the 1–5 perfect fifth (A), to which the octave can be added, 1-5-1 (B). A perfect fourth 5-1 (C) is also a power chord, as it implies the "missing" lower 1 pitch. Either or both of the pitches may be doubled an octave above or below (D is 5-1-5-1), which leads to another common variation, 5-1-5 (not shown).
Spider chords
thumb|Spider chord on D and B . The "web" of lines in the tab between each successive fret shows the fingering order (5-6-7-8 fingered 1-2-3-4 on strings 5-6-4-5).|175x175px
The spider chord is a guitar technique popularized during the 1980s thrash metal scene. Regarded as being popularized and named by Dave Mustaine of Megadeth, it is used to reduce string noise when playing (mostly chromatic) riffs that require chords across several strings. The chord or technique is used in the songs "Wake Up Dead", "Holy Wars...The Punishment Due", and "Ride the Lightning".
<pre>
D5 Bb5
e|-------|
B|-------|
G|-------|
D|-7-----|
A|-5--8--|
E|----6--|
3 <
1 4 <--Spider chord fingering
2 <
</pre>
As seen in the above tab, the two power chords may be played in succession without shifting, making it easier and quicker,