Hi guys, I'm hoping a better physicist than I can answer this question - the Doppler effect tells us that motion of either source or detector will cause a shift in perceived frequency. However, motion of the detector towards the source at some velocity will cause a different shift in frequency as compared to motion of the source towards the detector at the same velocity. In other words, v+vD/v is not the same as v/v-vS. But we also know from physics that velocity is not absolute and depends...
Doppler Effect and Velocity
Doppler Effect and Velocity