Complex sentence: The piano chord was a replacement for a failed vocal experiment: on the evening following the orchestra recording session, the four Beatles had recorded an ending of their voices humming the chord, but after multiple overdubs they wanted something with more impact.
Split into simpler sentences: The piano chord was a replacement for a failed vocal experiment. On the evening following the orchestra recording session, the four Beatles had recorded an ending of their voices humming the chord, but after multiple overdubs they wanted something with more impact.