Norwegian-inspired black metal guitarists usually favor high-pitched or trebly guitar tones and heavy distortion. The guitar is usually played with fast, un-muted tremolo picking. Guitarists often use dissonance—along with specific scales, intervals and chord progressions—to create a sense of dread. The tritone, or flat-fifth, is often used. Guitar solos and low guitar tunings are rare in black metal. The bass guitar is seldom used to play stand-alone melodies. It is not uncommon for the bass to be muted against the guitar, or for it to homophonically follow the low-pitched riffs of the guitar. While electronic keyboards were initially "not heard in [this] type of music", Dimmu Borgir say they started using keyboards "in the background" and then started using them as a "proper instrument" for creating "atmosphere". Some newer black metal bands began raising their production quality and introducing additional instruments such as synthesizers and even orchestras.