Both follow simple hard-rock , trading heavy riffing with guitar fills and solos. There are no other songs that have that bluesy riffing. Their sound is based on heavy organ, howling guitars, bass riffing and big drums. The group is known for its groove-heavy riffing and pitchshifted vocals. Now in their place are hackneyed synth passages and down tuned nu-metal style riffing. Double bass drums and "angular" riffing also defined the early work of Meshuggah. He is known for his fast, guitar-like riffing through heavy distortion. By combining '70s style hard rock riffing with alternative rock, Audioslave created a distinctive sound. There's no riffing or jamming going on. They also have used death metal traits such as low tuned and fast paced riffing. Mathcore is characterized by increased speed, technical riffing, and unusual time signatures. Nevertheless, the signature heavy riffing is also apparent. But "RiffTrax", the idea of riffing on topical movies, is a different thing. Kevin Murphy recalls the film as his introduction to the concept of riffing (MSTing). Each episode is one hour long featuring the three riffing on older National Geographic footage.