Hello! We are trying to verify if an acoustic standing wave has been established in a cavity. In order to do so, we are giving a constant frequency signal to a speaker. We are picking up the signal at two locations, one very close to the speaker(reference signal) and at a particular location(captured signal). We are cross correlating them. Ideally, we are supposed to get a zero phase difference between the two signals for the frequency sent in, proving that the reference and captured signals are varying simultaneously in time. However, we are getting a jump from -pi to pi at that frequency ?(here,its 520Hz). Could anyone explain what is happening? Thank you for taking your time for this!