Lots of people think DSP is hard, mostly because they learned DSP in college from professors who only understand it from a mathematical perspective. It's really not that difficutlt. If you have used iPhoto to tweak the brightness or contrast of a photo, you've done DSP. It's just mathematical manipulation of digital signals, and a digital photo is a digital signal.
We normally use DSP to test analog devices. Signal to Noise measurements, stereo separation, DAC and ADC linearity, all kinds of stuff. The one device you don't use DSP to test? A DSP chip! These are usually pure digital, so you just run a lot of patterns to verify functionality.
I published a new book, Harmonics: How they are made. It's available on Amazon.com in paperback and Kindle.
I published a book on DSP and analog! Distortion, The Cause Of Harmonics And The Lie Of THD is available on Kindle and Print