Trios exist, with one person doubling on vocals, but they do not have the overall stage presence of a band with a frontperson, so they tend to be less popular. (Example: Motörhead;)
Many bands have two guitar players, and, optionally, a synthesizer player.
Hard Rock is usually, but not always written with major key song construction, as opposed to heavy metal, which is often minor key oriented. There is a heavy reliance on the pentatonic scale for most elements of song construction, and fifths (power chords) are often substituted for traditional chords. Chord progressions are commonly associated to 1-4-5 degrees of the scale, as in rock & roll.
It is typified by a bright, trebly overdrive distortion effect on the guitars, lending to its overall sound. Drums can range from 100-150 Beats Per Minute, with 120 BPM being typical. Bass is usually round and warm sounding.
The guitar solo is very important part of a hard rock song, and leads to the credibility of the song just as much as the lyrics and vocal melodies do. Songs are generally hook laden, and consist of:
an intro
verse
chorus
verse
chorus
solo
chorus
an ending
There is much room for variation, and repetition of verses and choruses.
Jazz, Blues, and rock & roll were the roots of this style, as with heavy metal.
Punk rock, Gothic rock, Industrial music, funk, and fusion also claim these roots, but branch off at different points, eliminating elements that are considered unnecessary, and adding elements to typify their genre. Interestingly, death metal and industrial music also incorporate a march rhythm.
