Since New York audiences in recent years have been hearing a great deal of Elliott Carter 's most complex works , it was a good idea to perform '' Warble for Lilac-Time , '' a setting of Walt Whitman composed in 1943 when Mr. Carter was still under the sway of Copland and company , though even in this early song you encounter a formidably intellectual composer unable to constrain himself from filling the difficult piano part with tumultuous activity .