Complex sentence: Jim Thirlwell, who had contributed synth-noise to their album, went on to form Foetus; he played the Wasp, a battery-powered portable synthesizer with a built-in speaker.
Split into simpler sentences: Jim Thirlwell, who had contributed synth-noise to their album, went on to form Foetus. He played the Wasp, a battery-powered portable synthesizer with a built-in speaker.