Input (grade 13): In the late 1950s and early 1960s, the development of the Westrex single-groove stereophonic record cutterhead led to the next wave of home-audio improvement, and in common parlance, stereo displaced hi-fi.
Output (grade 5): In the late 1950s and early 1960s, Westrex invented the single-groove stereophonic record. This led to the next wave of home audio improvement.