In the 1950s Riley was already working with tape loops, a technology still in its infancy at the time; he would later, with the help of a sound engineer, create what he called a "time-lag accumulator". He has continued manipulating tapes to musical effect, in the studio and in live performances throughout his career. An early tape loop piece titled "Music for the Gift" (1963) featured the trumpet playing of Chet Baker. It was during Riley's time in Paris, while composing this piece, that he conceived of and created the time-lag accumulator technique. He has composed using just intonation as well as microtones. In New York City in the mid-1960s he played with his longtime friend La Monte Young, as well as with John Cale and tabla player Angus MacLise, who were founding members of The Velvet Underground. Riley is credited as inspiring Cale's keyboard part on Lou Reed's composition "All Tomorrow's Parties", which was sung by German actress Nico and included on the album "The Velvet Underground and Nico", recorded in 1966.