Of course you can learn the foundations without college and not learn them with college, but on average it's much easier to do so with that.
When I started my career as a scientist in a corporate analytical lab 36 years ago, corporate funding for travel and continuing education was plentiful. When budgets got tight, that was the first to go. Those of us who were self-directed learners survived the downsizing and cost-cutting much longer than those who didn't.
That’s all well and good until they find themselves competing with people from other countries who are being trained to hit the ground running and are willing to work for less....
14 chapters of Digital Signal Processing in 12 weeks w00t!
For many of my engineering courses at a top tier public university it was in-one-ear-out-the-other.
Though, the most of stuff I learned at community college (pre-engineering) did stick.