To me, true “heavy metal” begins with Black Sabbath; it is with Tony Iommi’s distinct dark and distorted style of guitar playing and amplified sound, along with Geezer’s depth in bass and haunting lyrical content, the indomitable Ward’s violent aggressive blues approach to the drums and then there was Ozzy, as was Elvis to Rock & Roll so was Ozzy to heavy metal.
Tony Iommi was influenced by “Blues” but in many of the songs that he created for Sabbath have a “Classic Music” feel to them like Baroque or classical guitar (Segovia or Paganini). In fact many of the Brits contributed a distinct classical music influence to rock music (Beatles, Stones, Procul Harum, Moody Blues, Pink Floyd and on to Led Zeppelin, Yes and Sabbath) quite different than America’s Americana (folk, blues, gospel, country, etc.) influence to Rock music. With the exception of Frank Zappa and a couple of others, the music of “Classic Rock” was created by the mix of British Bands with the United States Americana bands.
Tony Iommi simultaneously started a sound. A distinct sound of heavily distorted, dropped tuned, guitar using repeating riffs, motifs or themes (or Ostinato, in classical music), with strong emphasis on syncopated rhythms. The musical phrases or riffs of the guitars, when strummed give a big wall of sound (especially with a wall of stacked Marshalls), and then when played muted, the sound gives a distorted kind of chug chugging or crunch sound. This crunch sound of an extended musical repeating riff is what really differentiates “Heavy Metal” from “Hard Rock’s” 12-bar blues phrasing.
Another important differentiator between hard rock and heavy metal is the absence of the 12 bar blues, or the happy chord structures derived from I, IV, V chords that is so well used in rock. Now in place are original riffs being played over the vocalists extended melodies or rhythmic chants.
Also, the chord structures were in unexplored regions of minor, diminished, augmented, altered and complex chords, dissonance now ruled the songs along with the forbidden tri tone (Augmented fourth/Diminished 5th chords, “Devil’s Chord” or Diabolis en Musica, if you will), “heavy metal” crunches along in sometimes one key only or an ascending or descending or elaborate scalar riff off a low drone note (Jimmy Page is famous for this) or an elaborate riff that jumps, twists or winds through strange arpeggios (like the arpeggios accompanying that dark riff at the end of The Beatles song “I Want You (She’s So Heavy)” on the Abbey Road album or the arpeggios on Sabbath’s “Snowblind” off of the Vol. 4 album.
The drums had been getting more aggressive with a line of drummers starting from early instrumental and “surf rock” songs through to Ringo’s innovative close miked or ringing sounds. Next, Keith Moon of the Who popularized the (in his case) excessive or extensive usage of drum fills as did Cream’s Ginger Baker. Mr. Baker also roused us with his jazz influenced attack, as did the Jimi Hendrix Experience’s, Mitch Miller who was an eclectic and innovative compliment to Jimi’s genius. Then Led Zeppelin’s John Bonham perfected “Hard Rock” drumming while Black Sabbath’s Bill Ward invented “Heavy Metal” drumming. Both Bonham and Ward were jazz and blues influenced yet they were both in what would be seen as two different genres Rock & Metal respectively.
As far as “heavy metal’ drumming is concerned, jazz and blues were a big influence on the genre. In particular, how Sabbaths musicians (Bass, drums, and multiple guitars) used a slower tempo interspersed with wild, fast paced, freak outs only to come down again and use a great technique in metal song building of “recurring themes”, built out of a growing vast library of metal riffs.
The bass guitar is heavily influenced by the mix of blues but also of classical music. With much of the British Invasion the bass guitar was taking an active role in being a lead instrument as well as doubling as a rhythm instrument. Many heavy metal bands use Geezer’s pioneering style of bass playing by being proficient as a lead but with an ear to the classics and the whole picture. The UK in my opinion invented “Heavy Metal” by mixing classical music element with blues based psychedelic hard rock.
The lyrical content and imagery are quite extreme, far from the “I Want To Hold Your Hand” standard rock & roll pop tunes. “Metal’s” songs are basically from horror films, Halloween, the Occult, magic, anti-social philosophy, insanity and any taboo. Yes, the lyrical content is macabre, and downright disturbing, obscure and in many cases too harsh for modern society, especially in the early seventies despite the changes. Black Sabbath lived in obscurity for a long time in the early 70s, reveling in anti-social lifestyles and was re-discovered by a younger generation (the Baby Boomer’s children) in the 80s. With “heavy metal” lyrical topics, there is an “anything goes” attitude. The more shocking, horrifying, grotesque the better; anything goes even if society isn’t ready for it!
So, to recap “Hard rock” uses blues or R&B derived rock & roll phrasing. Listen to the 70s bands like in songs by Kiss in its original lineup and much of Queen in its early work, Boston, Aerosmith, Styx, Kansas, Thin Lizzy, Bachman Turner Overdrive, UFO, Rainbow , Bad Company, Foreigner and on they have heavy elements and some have outright true heavy metal songs, but for the most part these bands were hard rock bands, not metal (with the exceptions of Deep Purple which eventually would become strictly metal and Rush which would start out metal and go the other way to rock and even pop later) .
Whereas bands like, Budgie, Deep Purple’s (Mach II), Judas Priest, some of Lemy era Hawkwind progressing on to when Lemy founded Motorhead, Iron Maiden, early Rush, Dio era Rainbow, all adhere to ethos the original lineup of Black Sabbath established with specific parameters to the newer unexplored dimensions of music sound and composition.
Black Sabbath, is where, in my opinion, heavy metal started to be distinct and different in sound, culture and tradition from the more rock & roll oriented genre “hard rock”. There are many genre defining bands that played hard rock and dabbled in what was until then described as “that heavy sound” as Lennon had referred to it. That heavy sound, utilized through volume and distortion effects in the late 60’s, was what gave birth to two distinct genres, Hard Rock & Heavy Metal.