[1] The Eltro was the first machine capable of changing audio pitch (frequency) and speed (time) independently of each other.
Using the Eltro, a recording engineer could control the length of a commercial without changing the pitch or adding or removing silence.
[3] The Beach Boys used it to for high-pitched vocal effects on the song "She's Goin' Bald", recorded in Los Angeles in 1967.
In the film, both the pitch and speed of HAL's voice gradually drop at different rates while the computer is deactivated.
With the widespread availability of digital recording in the 1980s, it got easier to control pitch and speed with software while avoiding expensive, special analog tools.