Spectrum is 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. On 7 August 2013 Bill Putt died, after a heart attack.

Spectrum were formed in April 1969 in Melbourne, as a progressive rock group, by Mark Kennedy on drums (ex-Gallery), Lee Neale on organ (ex-Nineteen87), Bill Putt on bass guitar (ex-Gallery, The Lost Souls), and Mike Rudd on guitar, harmonica and lead vocals (ex-Chants R&B, The Party Machine, Sons of the Vegetal Mother). Initially the group drew on the work of contemporary bands such as Traffic, Soft Machine and Pink Floyd; they played cover versions of their material. Spectrum developed their own style as Rudd began writing original material. Alongside Kennedy’s drum solos, Putt’s bass playing and Neale’s keyboard work, a feature of Spectrum’s sound was Rudd’s guitar playing — he eschewed the near-universal use of guitar picks – using a finger-picking style on a vintage Fender Stratocaster to develop a characteristic sound.