"The trill [is] a technique that early composers used due to its rhythmic, melodic, and harmonic properties. By rapidly alternating between two adjacent notes—usually a half-step or whole-step apart—composers could create a brief sense of dissonance and tension that clashed with the tonality of the respective piece. The trill naturally creates a sense of tension, and when used properly, it lends itself well to somber moods and melodies. Metal musicians picked up on this early on and, by passing it down through the airwaves, have made it a hallmark of heavy music today."