▁" Har per ▁is ▁a ▁ter r ific ▁song writer , ▁but ▁a ▁bit ▁cra zy ". ▁ ▁Har per ' s ▁first ▁tour ▁of ▁the ▁United ▁States ▁followed ▁the ▁release ▁of ▁his ▁fourth ▁studio ▁album , ▁Fl at ▁Bar o que ▁and ▁B ers erk . ▁The ▁album ▁included ▁the ▁track ▁" An other ▁Day ", ▁a ▁song ▁dest ined ▁to ▁be ▁performed ▁live ▁by ▁Har per ▁for ▁many ▁years ▁to ▁come , ▁and ▁covered ▁by ▁several ▁other ▁artists ▁including ▁Elizabeth ▁F ras er ▁and ▁Kate ▁Bush . ▁The ▁album ▁also ▁featured ▁the ▁Nice ▁on ▁the ▁track ▁" H ell ' s ▁Ang els "; ▁its ▁eth ere al ▁sound ▁achieved ▁by ▁a ▁w ah - w ah ▁ped al ▁attached ▁to ▁Har per ' s ▁ac oust ic ▁guitar . ▁ ▁After ▁the ▁Bath ▁Festival ▁of ▁ 1 9 7 0 , ▁Led ▁Ze ppel in ▁paid ▁t ribute ▁to ▁Har per ▁with ▁their ▁version ▁of ▁the ▁traditional ▁song ▁" Sh ake ▁' Em ▁on ▁Down ". ▁Ret itled ▁" H ats ▁Off ▁to ▁( Ro y ) ▁Har per ", ▁it ▁appeared ▁on ▁the ▁album ▁Led ▁Ze ppel in ▁III . ▁According ▁to ▁Jimmy ▁Page , ▁the ▁band ▁adm ired ▁the ▁way ▁Har per ▁stood ▁by ▁his ▁principles ▁and ▁did ▁not ▁sell ▁out ▁to ▁commercial ▁press ures . ▁In ▁mut ual ▁appreci ation ▁of ▁their ▁work , ▁Har per ▁would ▁often ▁attend ▁live ▁performances ▁by ▁Led ▁Ze ppel in ▁over ▁the ▁subsequent ▁de cade ▁and ▁contributed ▁sle e ve ▁phot