The Boys' second guitarist, Rowland S. Howard, joined in 1978, and about this time, the group's sound changed dramatically. The addition of Howard's guitar was certainly a catalyst (his later use of audio feedback being a hallmark of the group) but there were other changes, as well: their sound drew upon punk, rockabilly, free jazz and the rawest blues, but defied concise categorization. Many songs were driven by prominent, repetitive basslines and frenetic, yet minimalist, drumming. Though the band was tightly rehearsed, the instrumentalists often sounded as if they were on the verge of collapse, this quality only emphasising the newfound mania of Cave's singing, and his expressionist lyrics. In producer/engineer Tony Cohen they found a willing accomplice to their experimentation and their refusal to repeat themselves; and in manager Keith Glass they found an enthusiastic financial backer. Glass' label Missing Link Records released all of the early Birthday Party records.