Hey fellow handmadeheroers,
just wanted to share a great free book that I found pretty useful when I was doing audio stuff: http://dspguide.com/

I found it quite a while ago, so I am not sure whether it is still relevant or if there are more modern resources. If you have specific questions I suggest you ask here: http://www.kvraudio.com/forum/

Again, it's been a while since I used it, but it seems still quite active.

Cheers,

Marco