audio - Calculate Phase angle between two signals i.e. digital Phase meter

I want to calculate the phase difference between the two channels(signals) of a stereo audio file.(uncompressed data i.e. PCM samples).

I want to determine whether whether two signals are in phase or not i.e. kind of digital phase meter ? Not the exact phase difference.

Can you please suggest a algorithm to calculate the phase difference.

Added--

What I'm expected to identify is Phase difference between signals (due to noises , disturbances) recorded separately then feed to left and right channel.