His style, as revealed in ``Riccardo III'' (his sixth opera), is derived in essence from Stravinsky's neoclassic and polytonal/polyrhythmic periods, an expression also predisposed to rhythmic qualities somewhat akin to those of Carl Orff and Robert Kraft, including a large variety of solo drum sounds, catchy figures for the xylophone, and the use of the piano for special percussive effects. Testi's melodic lines in the arias often seemed to consist of simple sequences - short melodic figures repeated on different pitch levels - and everyday vocal exercises.