Ask HN: Best resources for non-video based math self-study

Hi, I'm doing a Master's in Music Tech and need to get my math up for DSP programming. I'm trying to find good self-paced online courses that aren't video based. I just want to read text. I need to go back to basics because it's been 30 years, but I want to be able to go through content quickly because I was an A+ math student 30 years ago! Any recommendations? The goal is to get to be able to do university level DSP, assume I've forgotten stuff right back to senior high school.