Super common terms for analog media, tape in various forms (like reel to reel) is very old after all, and it's easy to imagine that the motors driving them exhi

Super common terms for analog media, tape in various forms (like reel to reel) is very old after all, and it's easy to imagine that the motors driving them exhibit significant speed variations during playback. There were also dedicated wow and flutter meters that measured both: You'd play a fixed frequency tone and it would display the frequency variation of what actually came out. Technically that's a form of frequency modulation, with wow and flutter being modulated with low and high frequencies respectively[1]. Later "quartz locked" high precision drives for example got rid of most of it, but as I recall that got widespread briefly before or even at the same time as CDs, and was far from ubiquitous. [1] The "high" frequency here still being much lower than what you usually think about when you read "high frequency" even in an audio context.