Complex sentence: Chapin's first formal introduction to music was while singing in the Brooklyn Boys Choir, where that Chapin met "Big" John Wallace, a tenor with a five-octave range, who later became his bassist, backing vocalist, and his straight man onstage.
Split into simpler sentences: Chapin's first formal introduction to music was while singing in the Brooklyn Boys Choir. It was here that Chapin met "Big" John Wallace, a tenor with a five-octave range, who later became his bassist, backing vocalist, and his straight man onstage.