Calculating time difference in sound input from multiple microphones

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C#

time

audio

I have a C# project that takes multiple (2 at the moment) microphones as an audio devices, detects sound from them, processes their audio frames with Fourier Transform and displays them. It also prints them in three colors: red is for microphone that has stronger input, green is for microphone that has weaker input and grey is for frames that arent strong enough to be of any interest.

Next step of my project is to calculate the time difference of sound samples that arrive at each microphone. For example if i speak directly to one microphone and the other is 3 feet away, the difference should be about 3 ms (assuming sound speed at 1feet/ms). This is of course just an example.

Can anyone help me with this? I've made my project based on this: Sound visualizer in C#