in the same position. tried to get into deep learning last year and found my calculus knowledge lacking. If you're looking to get back into it efficently, checkout mathacademy.com. i'm currently doing it myself and I'm on track to make another stab at getting into deeplearning next year.
https://upload.wikimedia.org/wikipedia/commons/3/3f/Sallen-K...
Super simple, really stable, and very easy to calculate. The cutoff frequency and Q can be set independently, and while making the cutoff variable can be tricky (as seen in various analogue synthesizers) you can vary the Q by varying the gain of the amp. If you assume it's just a unity gain buffer (in some designs it's just an emitter follower) getting the component values is easy.
The 101 of analog signal filtering - https://news.ycombinator.com/item?id=40946165 - July 2024 (20 comments)
(p.s. reposts are fine after a year or so; links to past threads are just to satisfy extra-curious readers!)
If you can calculate what a resistor network does, or get a computer to do it, you can also calculate what a filter does (and you'll definitely want a computer for that).
(Going backwards, from a desired frequency response to a filter design, takes more learning. Luckily some very smart people already designed filter templates where you can just plug in the frequency you want)
