How to get started analyzing audio signals for detecting cracks in a material?
Not really a programming question!

In any case if you need to read books to understand DSP and are trying to compare two non stationary processes I suggest you start reading right away because most steps I tell you won't make sense and you need to answer a host of questions even before anyone can answer this question.

Signal processing deals with lot of statistical phenomena and you have to work with it emperically many a times. Not to say there are no fixed rules but the step-by-step to process this signals is hard enough when data is stationary. Given that you have non stationary data, get reading and once you have a hang of it ask some pointed questions on dsp.stackexchange.com