Complex sentence: In some cases he used live musicians to provide a soundtrack; one group, the Falling Spikes, who played for a Heliczer multimedia installation called "The Launching of the Dream Weapon" in April 1965, later became the Velvet Underground.
Split into simpler sentences: In some cases he used live musicians to provide a soundtrack. One band, the Falling Spikes, who played for a Heliczer installation called "The Launching of the Dream Weapon" in early 1965, later changed their name to the Velvet Underground.