Complex sentence: Mike Hedges started his career as a tape-op at Morgan Studios in London in the late 1970s, graduated to engineer, went freelance in 1981 and quickly moved on to make his mark as an engineer/producer.
Split into simpler sentences: Mike Hedges started his career as a tape-op at Morgan Studios in London in the late 1970s. Having graduated to engineer, Hedges went freelance in 1981 and quickly moved on to make his mark as an engineer/producer.