text: This is what is called the Doppler Effect. All you really need to answer this question is a simple equation:\nf = f0 [(S +/- So)/(S -/+ Ss)]\nWhere f is the observed frequency, f0 is the frequency of the source, S is the speed of sound, So is the speed of the observer (+ if moving towards, - if away), and Ss is the speed of the source (- if moving towards, + if away).