Characteristics of progressive rock

Form

Progressive rock songs often avoid common popular music song structures of verse/chorus form, and their extended lengths allow complex themes that cannot be fully developed within the span of a three-minute single. Musical forms are blurred through the use of extended sections and of musical interludes that bridge separate sections together, which results in classical-style suites. These large-scale compositions are similar to medleys, but there is typically more thematic unity between the sections. Transitions between electric and acoustic sections provide dynamic contrast. Extended instrumental passages often mix composed, classical-style sections with group improvisation. These sections emphasize group virtuosity rather than individual skill, and they are a break from other pop forms in which a single, dominant singer or soloist is accompanied by a band.

These extended pieces are usually considered to be the result of experimentation with classical music forms, although an alternative viewpoint holds that they are explorations of the complexities possible within the popular music format. Many bands did, however, use compositional techniques borrowed from classical music. Elements of classical music are sometimes borrowed for the cultural significance they carry.

Traditional

Early progressive rock groups expanded the timbral palette of the then-traditional rock instrumentation of guitar, keyboard, bass guitar, and drums by adding instruments more typical of folk music, jazz or music in the classical tradition. A number of bands, especially at the genre's onset, recorded albums in which they performed together with a full orchestra.

Progressive rock bands often use instruments in ways different from their traditional roles. The role of the bass may be expanded from its traditional rhythm section function into that of a lead instrument. Bassists often play contrapuntal lines that are more independent and melodic than conventional bass lines, which emphasize the chord root. This is often accompanied by the use of an instrument such as a Rickenbacker bass, whose sound contains an unusually large amount of treble frequencies. Some bassists use the Chapman Stick, which is operated with both hands on the fretboard and allows polyrhythmic and chordal playing. Treble may be emphasized by the choice of strings, by playing with a pick, and by use of the instrument's higher registers. Drum kits are frequently expanded with orchestral percussion such as timpani and gongs. Acoustic guitar becomes more prominent and often appears as interludes played in the classical style of Andrés Segovia. Piano is played in a style derived from the classical piano repertoire rather than from the blues or boogie-woogie styles previously in use. Guitar may be dispensed with altogether, and traditional rhythm guitar is almost never used, as chordal backgrounds are typically played on a keyboard instrument such as the Hammond organ.

Electronic

In the 1960s, it was impractical to work together with an orchestra on a regular basis. As a substitute, the Mellotron is a keyboard instrument that contains tape-recordings of individual notes of various instruments and voices, and plays back their sounds as the keyboard is pressed. Its sounds included woodwinds, choirs, brass and, perhaps most famously, strings. The technology available meant that its sounds were not exact reproductions of the instruments, but instead had a haunting quality that many bands prized.

The Hammond organ is another instrument closely associated with progressive rock. It is a versatile instrument that can function like a pipe organ, can be played through a guitar amplifier for a distorted tone, is capable of sustained notes and rapid melodic runs, and can make percussive sounds. The ability to adjust its timbre while a note is held and its capabilities of vibrato and, when a rotating Leslie speaker is used, tremolo, make it a very expressive lead instrument. The use of organs and choirs reflects the background in Anglican church music shared by many of the genre's founders. Various other electronic and electro-mechanical keyboard instruments were in common use.

The birth of progressive rock roughly coincided with the commercial availability of synthesizers. Early modular synthesizers were large instruments that used patch cords to route the signal flow. Programming the instruments meant placing the patch cords to connect the individual modules. The Minimoog, a smaller, simplified synthesizer that needed no patch cords, began production in 1971 and provided keyboardists with a more-easily programmed instrument that could imitate other instruments, could create new sounds of its own, and was highly portable and affordable. Progressive rock was the genre in which the synthesizer first became established as a common part of popular music. Synthesizers could be used to play the rapid, virtuosic lines that changed the perception of keyboard instruments.

The reliance on the use of multiple keyboard sounds meant that some keyboardists appeared onstage surrounded by ten or more keyboards. Modern digital synthesizers and samplers have reduced the need for huge keyboard stacks, as they typically allow sounds to be layered or for one keyboard to trigger another's sounds through a MIDI connection. They also provide a reliable alternative to instruments such as Mellotrons, whose delicate mechanical apparatus is prone to breakdowns, and are much more portable than bulky instruments such as the Hammond organ. Digital synthesizers are also suitable chordal instruments, unlike early analog synthesizers such as the Minimoog, Moog Taurus and ARP Odyssey, which could play only one note at a time and so were mainly suitable for drones, basslines and lead playing.

The concept of the studio as an instrument led certain audio effects units to become identified with progressive rock. Progressive rock guitarists showed a distinct preference for Hiwatt amplifiers. Advancements in recording technology were key in enabling the production of progressive rock albums. As multitrack recording with as many as 64 separate tracks became available, bands took advantage of the additional tracks and created increasingly dense arrangements.

Rhythm, melody and harmony

There is a tendency towards greater freedom of rhythm than exists in other forms of rock music. Progressive rock artists are more likely to explore complex time signatures such as 5/8 and 7/8. Tempo, key and time signature changes are common within progressive rock compositions. Complex time signatures are sometimes used to create a polyrhythmic effect. Progressive rock often discards the blues inflections and pentatonic scale-based melodies of mainstream rock in favor of modal melodies. Compositions draw inspiration from a wide range of genres including classical, jazz, folk music and world music. Melodies are more likely to comprise longer, developing passages than short, catchy ones.

Chords are typically standard triads, although many keyboardists would alter these triads by playing a nonchord tone in the bass. Chord changes are typically based on modes, as is typical of rock music, and deviate significantly from the tonality of music from the classical era. Unexpected chord changes in the style of impressionist composers like Claude Debussy are common.

Lyrical themes

Progressive rock lyrics tend to avoid common rock and pop subjects such as love and dancing. Bands also avoid such youth-oriented themes as violence, nihilism, rebellion, and the macabre. Sex is not a common subject. Themes found in classical literature, fantasy and folklore occur frequently, and intellectual topics such as psychological theories may be addressed. Romantic poetry and J. R. R. Tolkien are frequent sources of inspiration.

Medievalism and science fiction themes are common and often appear as metaphors for spiritual transformation and the quest for an ideal society. Many early lyrics express utopian themes that reflect the genre's origins in psychedelic rock and address the subject of spiritual transformation. Spiritual and religious themes are common. Monty Python and Bonzo Dog Doo-Dah Band-influenced humour appears in some progressive rock lyrics. This is especially pronounced in the more eccentric, Dadaistic approach adopted by some of the Canterbury bands. Several groups valued lyrics so strongly as to employ a lyricist as a full-time band member.

Social commentary is frequently present. Many progressive rock bands were strongly rooted in British folk music, and this resulted in a tendency toward pastoralism in the lyrics. As social and economic problems increased in Britain within the 1970s, many artists gravitated away from pastoralism and ecology at varying degrees, with temporary to near-permanent shifts towards modernism, contemporary political satire, and realism. Awareness of nature sometimes combined with social criticism to produce lyrics that expressed concern over the ecology. Ecological themes were sometimes carried out to an extent that even genre fans found embarrassing, and they were frequently satirized by Frank Zappa as naive.

Concept albums

The late 1960s and early 1970s saw a general trend among rock and pop artists toward albums in which many or all of the songs shared a common theme. This tendency was especially pronounced in progressive rock. Experimentation with expanded musical forms contributed to this, as songs that were more or less thematically related were often combined into suites made up of several movements.

These extended pieces carry on in the Romantic-era tradition of program music, which is intended to tell a story, and they often are inspired by works of literature. Story arcs are sometimes spread out over several albums. The advent of multi-part suites that occupy an entire LP side roughly coincided with the rise of FM radio and its practice of playing albums, or album sides, in their entirety. Some bands stretched the format beyond their audiences' capacity to tolerate.

Stage presentation

Some bands had elaborate stage presentations. Some acts indulged in pure showmanship. Progressive rock visual styles sometimes extended to the stage sets. This enthusiasm for showmanship was not shared by all progressive rock bands.

Album art

Album covers prior to the Beatles' Sgt. Pepper's Lonely Hearts Club Band usually consisted of a photograph of the group, but the trend toward concept albums was accompanied by a move toward artwork that depicted the album's concept. This artwork often contains science fiction and fantasy motifs executed in a surrealist style.

A number of artists became closely associated with the genre. Artwork was sometimes commissioned from artists who were famous in their own right. This combination of music and artwork is intended to function as a total work of art, which is a further use of concepts borrowed from high culture. The practice of connecting an album's artwork to its concept still exists, but its effectiveness is limited by the smaller display area used by compact discs and mobile devices.