I recommend Prandoni & Vetterli's coursera class on Signal processing[1]. They have really made an effort to teach this in an intuitive manner instead of just throwing equations at you. This was the course where I finally really understood Fourier transforms in a visual way.

The other course I recommend is the Audio Signal processing class by Xavier Serra[2] This is a practical class with lots of hands on programming examples and introduction to useful open-source software tools.

[1] https://www.coursera.org/learn/dsp [2] https://www.coursera.org/learn/audio-signal-processing