Sent in an application, got an email three weeks later, a phone interview the next week. It was done by the first question. (I'm surprised I was even interviewed for this position). The interviewer was very friendly and personable and totally not antagonistic in spite of my lack of knowledge. This just wasn't the job for me, no big deal. There was a virtual whiteboard and a computer was required for the first phone interview. I spent the whole weekend before studying Fourier transforms of common signals, IIR/FIR filters and their responses, aliasing theory (and how to calculate aliasing frequencies), time/frequency tradeoffs when FFTs...it was over after one question. KNOW YOUR TRANSFORMS.