He advocated primarily Gregorian plainchant and polyphony. Ami singing is known for its complex contrapuntal polyphony. His choral compositions feature rich harmony, vocal polyphony, and imitation. Congregational psalm singing replaced the elaborate polyphony of trained choirs. Instruments featuring polyphony are said to be polyphonic. Instruments that are not capable of polyphony are monophonic or paraphonic. The synthesizer is monotimbral, with six voices of polyphony. The motet would become the most popular form of medieval polyphony. The interaction of sung voices in Renaissance polyphony influenced Western music for centuries. Such a perspective considers homophony as a sub-type of polyphony. Isorhythm is a logical outgrowth of the rhythmic modes that governed most late medieval polyphony. This type of polyphony (counterpoint) is also rare in contemporary popular styles. The Kyrie consists of imitative polyphony in Palestrina's earlier style, based on the main motif. The Prophet-5 uses five voices of polyphony. Rather than being fixed works, they indicated ways of improvising polyphony during performance.