Start with But what is a convolution? (23 min, 3Blue1Brown), then But what is the Fourier Transform? A visual introduction. (20 min, 3Blue1Brown). All 250 lessons here are free, from the teachers' own official uploads. You'll need laptop stand, noise-cancelling headphones, second monitor and a few more basics (about $270 of kit). The book to keep beside you: Mathematics for Machine Learning by Marc Peter Deisenroth.