Complex sentence: He is also well known for playing bass guitar (and contributing songwriting) for British rock band Oasis, on Oasis' last albums the band had less clearly defined roles and Bell was able to contribute guitar on his own songs.
Split into simpler sentences: He is also well known for playing bass guitar (and contributing songwriting) for British rock band Oasis. On Oasis' last albums, the band took less clearly defined roles and Bell was able to contribute guitar on his own songs.