I'm very interested in filter design and would like to learn more about them; however, I don't want to waste my time learning about them if there is no point. I already know the basics of filters and know how to use table etc to make particular filters. What I am wondering is, is there any justification for me to learn a lot about passive and active filters? These days, are there really any serious (not just a simple RC low pass) applications for passive and active filters or is it all DSP these days? I'd like to learn about it; however, if it's useless, then I think I'll go learn something else.
Could someone also recommend a good book?
I'm thinking: Filter theory and design: active and passive Adel S. Sedra, Peter O. Brackett