MATLAB: Additive white gaussian noise

additive white gaussian noiseawgndigital signal processingMATLABpsdwhite noise

Hello
I am using the "awgn" in my function to add noise to a signal. I need to describe and document the exact process of how the noise is added but I could not find any actual formulae on the matlab website that describes the function. I understand the syntax and how to use it but I don't understand how exactly does awgn distribute the noise ? Is it just a random number in a range ? Also what exactly does the snr input argument control ( I do understand that its signal to noise ratio but the noise is meant to be a random number so how does snr affect random number generation within the function ? ), does the PSD of the noise equal snr*signal-in ? Or is it the integral of the PSD ?
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