To some, Hard Rock and Heavy Metal are nearly interchangeable terms, since they share so many similarities. In both styles, loud, distorted guitars are prominent and the band is fronted by a lead singer who rarely plays another instrument. However, there's a key difference -- Hard Rock stays true to the bluesy rock & roll of the Stones and has a certain swing in the back beat. Heavy Metal has no swing -- it relies on brutal guitar riffs and pummelling rhythms.
Hard rock evolved in the late '60s, as psychedelia and blues rock began pushing the boundaries of amplification and blues-based riffs. Hard-Rock relies less on improvisation than blues-rock and it isn't as loud as heavy metal, even if it shared the same distorted guitars and long solos. In Hard Rock, it's the songs, rhythms, riffs and hooks that matter, and they should all be played as loud as possible.
Heavy Metal also derived from the shatteringly loud blues-rock and psychedelia of the late '60s. Metal sanded away most of the blues influences and leaving the powerful, loud guitar riffs. In the early '70s, heavy metal established itself as one of the most commercially successful forms of rock & roll. In the next three decades, metal adapted itself to the times and it never completely disappeared from the charts. At its core, heavy metal is an adolescent experience; teenagers -- primarily white males -- form the majority of its audience. Some critics dismiss metal as simplistic primal pounding. Certainly, a fair share of heavy metal is nothing but three-chord riffing, yet most metal bands place a premium on technical skill.
Metal guitarists have always been innovators in technique, speed, and skill. In every subgenre of heavy metal, the guitar is the center of the music. The songs are assembled around the riff, with the gutiar solo taking prominence. By and large, heavy metal is rock & roll with all of the roll stripped away -- the blues remains, but it doesn't swing. All of the rhythms are fairly rigid, almost military in origin. In every metal style, from pop-metal to thrash, bombast is the key -- from the drums to the guitars, it's about being as loud as possible.