I finished my undergrad 6 years ago and want to get into a PhD program in a year or two. I expect my research will pertain to DSP and involve FFT/DFT on a regular basis. To brush up on my math (PreCalc, Calculus, Linear Algebra etc), I've been watching Khan's videos nightly. I must say his videos are a great way to recollect what you've already understood once but forgotten now.

I wish there was a way to speed them up though. I've thought about downloading the mp4s from YouTube and playing them locally at high-speed with VLC.