
It's very comprehensive, but it's also very well written and walks you through the mechanics of Fourier transforms in a way that makes them intuitive.
So, I would suggest a better question is: where can I find an introduction to this stuff that is better aligned with my current understanding and knowledge. To that end, here's a great intro book: https://www.dspguide.com/
I read that cover to cover when I was 17 and I would not have been described as particularly mathematically gifted.
You got a BASIC code snippet for training and inference and mos of all, there is an explicit use-case for digital filter approximation! At the time NN were treated as a tool among other ones, not a "answer-to-everything" type of thing.
I know Deep Learning opened new possibilities but a lot of time CNN/RNN/Transformers are definitely not needed: working on the data instead and using "linear" models can go really far (my 2 cents)
[1]: https://www.dspguide.com [2]: http://www.dspguide.com/ch26.htm