They e-mailed me to set up a phone call. The phone call was about an hour. First, they asked questions about object oriented programming and other C++ questions like overriding, polymorphism, overloading. Then they asked audio and digital audio questions, mostly stuff related to sampling rates and bandwidth, and the results on the signal. Since this isn't truly my field, the biggest issue was understanding the jargon being used, as opposed to the concepts.