Power metal guitarists and bassists generally play rapid streams of notes, but change chords comparatively slowly, with a harmonic tempo of once per measure or slower. Fast and technically demanding guitar solos, however, are almost guaranteed. The slow changing of chords is significant in defining power metal just as the fast rapid chord changes often define traditional thrash metal. Power metal often makes use of Major chord progressions as well as circle progressions. Some of the most influential and acclaimed power metal guitarists are Kai Hansen of Gamma Ray, Michael Weikath of Helloween, and Timo Tolkki formerly of Stratovarius. It is a common trait in power metal for the bass guitar to take a back seat, so to speak; often simply providing the chord root notes and being drowned out by the more prevalent rhythm guitars. However, some power metal bands incorporate bass that is more audible with colorful patterns distinct from the rhythm guitars, such as Helloween, Hibria, and Symphony X.