In 1961, the machine sang its first words. Surrounded by engineers and programmers, the IBM 7094 became the first computer to carry a tune. Now, as artificial intelligence sings covers of songs and creates them from nothing more than a prompt, we have come a long way since the earliest babbling of machine-generated music.

John Lennon and Paul McCartney sang together for the last time in The Beatles’ newest and final song, “Now And Then.” How was it possible to revive the voice of Lennon — and of George Harrison — on a new track?