thumb|alt=A color photograph of members of the band Yes on stage|Progressive rock band Yes performing in Indianapolis in August 1977 Progressive rock, a term sometimes used interchangeably with art rock, moved beyond established musical formulas by experimenting with different instruments, song types, and forms.R. Unterberger, "Progressive Rock", in Bogdanov et al., 2002, pp. 1330–31. From the mid-1960s the Left Banke, the Beatles, the Rolling Stones and the Beach Boys, had pioneered the inclusion of harpsichords, wind, and string sections on their recordings to produce a form of Baroque rock and can be heard in singles like Procol Harum's "A Whiter Shade of Pale" (1967), with its Bach-inspired introduction.J.S. Harrington, Sonic Cool: the Life & Death of Rock 'n' Roll (Milwaukee, WI: Hal Leonard Corporation, 2003), , p. 191. The Moody Blues used a full orchestra on their album Days of Future Passed (1967) and subsequently created orchestral sounds with synthesizers. Classical orchestration, keyboards, and synthesizers were a frequent addition to the established rock format of guitars, bass, and drums in subsequent progressive rock.E. Macan, Rocking the Classics: English Progressive Rock and the Counterculture (Oxford: Oxford University Press, 1997), , pp. 34–35.
thumb|alT=a color pHotogRaPH Of mEmBers of ThE banD yes oN stage|prOgResSIVe ROck Band yes PeRformING In inDiaNAPolIS in august 1977 pRogressiVe Rock, a term someTIMes usEd intercHaNgEabLy wIth aRT roCk, moved beyond eStaBlIsheD mUSicAl ForMulaS By experimeNting wiTh dIfFerent insTRuments, song types, and foRMs.R. unTERBErGEr, "prOgResSive ROcK", in bOgdaNov eT Al., 2002, Pp. 1330–31. FrOM ThE mID-1960S the left bANke, The beaTles, tHe RolLing StOneS and the bEaCh boyS, haD pIoNeerED the INClUsioN oF HaRPsiChORDS, wiNd, ANd stRiNg seCtIons oN theiR reCOrdinGS to pRodUCe A form Of bAroque rock and can be heard iN siNgLes lIke PrOcoL hArUM'S "a whIter SHade Of pale" (1967), with itS baCh-iNSpIred introduCtIOn.j.s. harrINgtoN, Sonic cOol: the lIfe & deaTH OF RoCk 'n' roLl (milWauKeE, wI: Hal leonard cOrpoRaTIoN, 2003), , P. 191. The MoOdY blUes UseD A FUll OrChEsTrA on ThEiR aLbum Days of future passED (1967) And suBSEQuentLy cReated oRchestral SouNDs wiTH sYnTHEsIzers. classical orChEstraTIoN, KeYboards, AnD synThesizERs were a FreQUeNt aDdiTion TO the eStABlisHed ROcK FormAt of GuitArs, bAss, AND drUms iN subsequenT ProGrESsive rock.e. MaCaN, rockinG thE classIcS: eNglish progRessIve rock and the countercUltuRe (OxfoRd: oxford uNiVersiTy press, 1997), , pp. 34–35.