linguistic:translation, quality:correction, stylistic:tone
Typical harmonic structures

Heavy metal is usually based on riffs created with three main harmonic traits: modal scale progressions, tritone and chromatic progressions, and the use of pedal points. Traditional heavy metal tends to employ modal scales, in particular the Aeolian and Phrygian modes. Harmonically speaking, this means the genre typically incorporates modal chord progressions such as the Aeolian progressions I-♭VI-♭VII, I-♭VII-(♭VI), or I-♭VI-IV-♭VII and Phrygian progressions implying the relation between I and ♭II (I-♭II-I, I-♭II-III, or I-♭II-VII for example). Tense-sounding chromatic or tritone relationships are used in a number of metal chord progressions. In addition to using modal harmonic relationships, heavy metal also uses " pentatonic and blues-derived features".

The tritone, an interval spanning three whole tones – such as C to F# – was considered extremely dissonant and unstable by medieval and Renaissance music theorists. It was nicknamed the diabolus in musica – "the devil in music".

Heavy metal songs often make extensive use of pedal point as a harmonic basis. A pedal point is a sustained tone, typically in the bass range, during which at least one foreign (i.e., dissonant) harmony is sounded in the other parts. According to Robert Walser, heavy metal harmonic relationships are "often quite complex" and the harmonic analysis done by metal players and teachers is "often very sophisticated". In the study of heavy metal chord structures, it has been concluded that "heavy metal music has proved to be far more complicated" than other music researchers had realized.