Differences have been identified between art rock and progressive rock, with art rock emphasizing avant-garde or experimental influences and "novel sonic structure", while progressive rock has been characterized as putting a greater emphasis on classically trained instrumental technique, literary content, and symphonic features. Compared to progressive rock, art rock is "more challenging, noisy and unconventional" and "less classically influenced", with more of an emphasis on avant-garde music. Similarities are that they both describe a mostly British attempt to elevate rock music to new levels of artistic credibility, and became the instrumental analog to concept albums and rock operas, which were typically more vocal oriented.