Hard rock and heavy metal both emerged in the 1970s. “Hard rock” is a pat term used to describe bands that have a hard-edged, powerful sound. It is the opposite of soft rock, which is generally more radio friendly, streamlined, and pop oriented. Hard rock is based on heavy-hitting drums, distorted guitars, and intense vocals. Improvisation—usually flashy guitar solos—is also a hallmark of hard rock.

Hard rock can be difficult to distinguish from heavy metal, its stylistic offshoot. Just remember that heavy metal is an extreme, over-the-top version of hard rock. Moreover, heavy metal is less blues based. In metal, guitarists generally favor pentatonics over bluesy scales. (A blues scale uses flatted thirds, fifths, and sevenths; pentatonics are consonant, five-note scales.) Because of this, metal guitarists are often referred to as “shredders.”

Heavy metal also favors power chords, which are nonspecific chords that do not contain thirds. On the other hand, hard rock employs chordal variety in addition to power chords. Furthermore, heavy metal bands often rely on hyper-fast speeds or very heavy, loping grooves. Hard rock is always “cutting,” but by comparison, it is less extreme and more diverse.

While powerful in nature, hard rock still tends to fall back on blues riffs, and it's not uncommon to hear dynamic (loud and soft) shifts in the music. This might include mellow sections or psychedelic, spacey elements followed by explosive playing. The music of Led Zeppelin is one example of this. Further, hard rock usually offers a melodic hook in the chorus of each song. While heavy metal also favors hooks, they may be less obvious to listeners, especially in later periods where the music blooms into all-out “speed metal” and “thrash metal.”

Some important hard rock bands are Led Zeppelin, Deep Purple, Rush, Van Halen, Aerosmith, Guns N' Roses, Soundgarden, and Alice in Chains. But be careful of labels in music. Guns N' Roses has also been branded “sleaze glam” and Soundgarden and Alice in Chains, along with Nirvana and Pearl Jam, are also pioneers of “grunge rock.” Grunge is a regional subset of a bigger, wide-open style of rock called “alternative rock.”

Other bands that walk the line between hard rock and heavy metal include AC/DC and KISS. Straight-up metal bands include the early British innovators Judas Priest, Black Sabbath, Iron Maiden, and Motorhead. Additional metal bands—popular in the mid-to-late 1980s—include Mötley Crüe, Def Leppard, Dokken, Pantera, Ratt, Quiet Riot, Slayer, Megadeth, and Metallica. Keep in mind that metal bands do not all play the exact same style(s). For example, Mötley Crüe, Def Leppard, and Ratt played “glam metal” or “hair metal.” On the other hand, classic Metallica is best described as “thrash metal.” One thread that weaves through all heavy metal is the size of the drum set. Double bass drums, large power tom-toms, and vast arrays of cymbals are universal features on heavy-metal kits.