Musically, the effects may be represented via novelty studio tricks, electronic or non-Western instrumentation, disjunctive song structures, and extended instrumental segments. Some of the earlier 1960s psychedelic rock musicians were based in folk, jazz, and blues, while others showcased an explicit Indian classical influence called "raga rock". Of the original acts of the 1960s, there was two main variants of the genre: the whimsical British 'pop-psychedelia' and the harder American West Coast 'acid rock'. While 'acid rock' is sometimes deployed interchangeably with the term 'psychedelic rock', it refers specifically to the heavier and more extreme side of the genre.
The peak years of psychedelic rock were 1966-1969, with the 1967 'Summer of Love' and the 1969 'Woodstock Rock Festival' demonstrating the movement at its height. The genre became an international musical movement associated with counterculture before beginning a decline starting in 1970 due to changing attitudes, the loss of several key musicians and a general back-to-basics movement in rock music; surviving performers moved onto different musical areas. The genre bridged the transition from early blues and folk-based rock to progressive rock and hard rock. The natural evolution of the style would lead to the development of 'heavy metal'.
Since the late 1970s it has been revived in various forms of 'neo-psychedelia'.
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