Describe the primary characteristics of hard rock and early heavy metal, detailing the differences in musical style and instrumentation.

Hard rock and early heavy metal emerged as distinct but related genres in the late 1960s and early 1970s, building upon the foundation of blues-rock but pushing the boundaries of volume, intensity, and aggression. While both styles shared some common characteristics, they also developed unique features in their musical approaches, lyrical content, and instrumentation.

Hard rock can be characterized by its emphasis on powerful, driving riffs, a strong backbeat, and blues-based melodic structures, although with more distortion and volume than traditional blues rock. It retained the basic instrumentation of rock and roll—electric guitar, bass guitar, and drums—but with a significant increase in amplification and a heavier sound. The guitar work was typically characterized by simple, catchy riffs, often using power chords and pentatonic scales. The drumming was straightforward, providing a solid rhythmic foundation for the music, typically emphasizing a strong, driving beat. Vocals in hard rock tended to be forceful and assertive, often delivered with a sense of swagger. Hard rock songs usually maintained a verse-chorus structure, albeit with an intensified energy, and were generally more concise than those found in progressive rock or early heavy metal. Bands such as Led Zeppelin, in their early work, epitomized many of these characteristics, blending blues influences with harder, louder sounds. AC/DC is another prime example, with its stripped-down, high-energy, and riff-driven approach, emphasizing a consistent, rhythmic power. Deep Purple also exemplified early hard rock, with its combination of blues influences, classical flourishes, and a powerful, driving sound. Tracks like "Highway Star" and "Smoke on the Water" showcase hard rock's driving rhythms and prominent guitar riffs. Other bands like The Who, while incorporating other influences, also contributed to the hard rock sound.

Early heavy metal, while building on the hard rock foundation, took the volume, distortion, and intensity to even greater extremes. Heavy metal often featured a more aggressive and darker sound with an emphasis on heavy riffs, faster tempos, and a more complex harmonic approach than hard rock. While hard rock often drew from blues scales and structures, heavy metal expanded into more dissonant harmonies and modal scales. The instrumentation was largely similar to hard rock, but with an increased emphasis on virtuosity and technical prowess, especially in guitar playing. The guitar work often featured faster, more complex riffs, using techniques such as sweep picking, tapping, and tremolo picking. The bass guitar played a more prominent role in heavy metal than in hard rock, often following the guitar riffs or providing a counter-melody. The drumming in heavy metal often featured double bass drumming, complex rhythms, and a louder, more powerful sound. Vocals in early heavy metal could range from powerful, soaring highs to raspy, growling lows, depending on the band. Black Sabbath is considered a pioneer of the genre, taking the heavy, dark sounds and themes of hard rock and exaggerating them to create a new sound with their use of down-tuned guitars and bleak lyrical themes. Led Zeppelin, particularly with tracks like "Whole Lotta Love" and "Rock and Roll," also contributed significantly to the early heavy metal sound with the band’s blend of blues, folk, and hard rock. Deep Purple's "Highway Star," while often considered hard rock, also contained many elements that would become hallmarks of heavy metal, like the fast tempo, virtuoso guitar playing, and intense vocals. Judas Priest, building on early heavy metal, further defined the genre with the twin guitar attack, use of leather and studs, and higher vocal ranges of the lead singer, Rob Halford.

A primary difference between hard rock and early heavy metal lay in their lyrical themes. Hard rock lyrics often dealt with more relatable subjects such as love, relationships, partying, and rebellion, with a tone that was often assertive and confident. Heavy metal, on the other hand, tended to explore darker and more fantastical themes, such as mythology, the occult, fantasy, and social alienation. While both genres used themes of rebellion, heavy metal often had a more nihilistic and apocalyptic edge.

Another difference was the use of distortion. Hard rock generally used a moderate level of distortion, while heavy metal often used higher levels of gain, creating a thicker, more aggressive sound. The overall aesthetic also differed between the two genres. Hard rock maintained a more straightforward, blues-rock-inspired image, while early heavy metal often incorporated more theatrics, such as leather, studs, long hair, and dark, occult imagery.

In terms of instrumentation, while both genres featured electric guitar, bass, and drums, heavy metal often utilized more complex instrumentation and technical playing skills. Double bass drumming, virtuosic guitar solos, and technically demanding bass lines were more prominent in heavy metal than in hard rock. While hard rock emphasized groove and powerful rhythms, heavy metal often emphasized speed and technical complexity.

In summary, hard rock and early heavy metal both built on the foundations of blues-rock, but they diverged in their approaches. Hard rock emphasized powerful riffs, a strong backbeat, and blues-based melodic structures, while early heavy metal took these elements to an extreme with greater volume, distortion, and intensity, and with a focus on virtuosic playing and darker themes. Bands like Led Zeppelin, AC/DC, and Deep Purple epitomized hard rock, while Black Sabbath, early Led Zeppelin, and early Judas Priest are prime examples of early heavy metal. Both genres played a crucial role in shaping the landscape of rock music and continue to influence modern bands.