Heavy metal guitar (or simply metal guitar) is the use of highly-amplified electric guitar in heavy metal. Heavy metal guitar playing is rooted in the guitar playing styles developed in 1960s-era blues rock and psychedelic rock, and folk harmonic traditions and it uses a massive sound, characterized by highly amplified distortion, extended guitar solos and overall loudness. The electric guitar and the sonic power that it projects through amplification has historically been the key element in heavy metal. The heavy metal guitar sound comes from a combined use of high volumes and heavy distortion.