Complex sentence: The first session saw the introduction of a new keyboard instrument called the Mellotron, acquired by Lennon, its keys triggered one of three tape loops for flutes, strings or choirs, enabling its user to play in those three voices.
Split into simpler sentences: The first session saw the introduction of a new keyboard instrument called the Mellotron. Acquired by Lennon, the Mellotron's keys triggered one of three tape loops for flutes, strings or choirs, enabling its user to play in those three voices.