Spectrum are an Australian progressive rock band which formed in April 1969 and broke up in April 1973. The original line-up was Mark Kennedy on drums, Lee Neale on organ (ex-Nineteen87), Bill Putt on bass guitar (ex-Lost Souls), and Mike Rudd on guitar and lead vocals (ex-Chants R&B, The Party Machine). In August 1970 Kennedy was replaced by Ray Arnott on drums. These members also performed under the alter-ego, Indelible Murtceps, from 1971 to 1973. Spectrum had a number-one hit, "I'll Be Gone" (January 1971), on the Go-Set National Top 60 singles chart. After Spectrum and Indelible Murtceps disbanded, Putt and Rudd formed Ariel. In 1999 the pair formed Spectrum Plays the Blues, which later trimmed their name back to Spectrum.