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In guitar music, a power chord (also fifth chord) is a chord that consists of the root note and the fifth. Power chords are commonly played on amplified guitars, especially on electric guitar with distortion. Power chords are a key element of many styles of rock〔("Glossary of Guitar Terms" ), ''Mel Bay Publications, Inc.'' "A chord consisting of the first (root), fifth and eighth degree (octave) of the scale. Power chords are typically used in playing rock music."〕 and especially heavy metal music.〔Heavy metal music〕 ==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).〔Doug Coulter (2000). (Digital Audio Processing ), p.293. ISBN 0-87930-566-5. "Any non-linearity produces harmonics as well as sum and difference frequencies between the original components."〕 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.〔("Distortion – The Physics of Heavy Metal" ), ''BBC''〕 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.〔Robert Walser (1993). ''(Running with the Devil )'', p.43. ISBN 0-8195-6260-2.〕 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 effect. Power chords also have the added advantage of being relatively easy to play (see "Fingering" below), allowing fast chord changes and easy incorporation into melodies and riffs. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Power chord」の詳細全文を読む スポンサード リンク
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