Thrash

Thrash Metal is a sub-genre of rock that focused on an aggressive, "underground" sound. This meant heavily distorted guitars, screamed vocals, and up-tempo songs with non-stop drumming. Guitars typically played riffs, rarely playing sustained chords. Riffs took inspiration from both blues and classical compositions. Fast guitar solos were also prominent. Rather than use rich harmonies for chorus sections, thrash typically built tension using rhythm drops, vocal-guitar point-counterpoint, or tempo shifts. Song structures often took experimental routes, sometimes omitting choruses altogether. Popular thrash artists are Metallica, Megadeth, and Pantera.

Riff-based Tonality

Thrash artists rarely played even basic triad chords, instead focusing on riffs. A riff at its most basic level is simply a repeating single-note melody line. While rock music generally expanded upon this, thrash took it to the next level. Given that heavy distortion tends to compress the sound, using conventional dynamics by altering picking strength provided little tonal difference. Additionally, thrash's absurdly fast tempos made it difficult to apply contrasting picking strength during a riff. Seeking contrast for the notes inside riffs, artists expanded some notes as power chords while palm muting others.

Scale

Tonality mostly came from the scale the riffs were played in.