As the step before a video diving into frequency modulation, I thought it was important to get everyone up to speed about how pitch & frequency relate to each other and are implemented not just in modular VCOs, but also under the hood of a lot of fixed-architecture synths.
If you've never really thought about how 440 hz turns into an A, why we use a volt per octave standard, or what's important about doubling the frequency of a pitch, then this video will help get you ready for the next video, all about Frequency Modulation.