Generation of noise floor file for estimating signal-to-noise ratio of a wave file
One method that is reasonable for white noise is to use a spectrogram. For each spectrum, compute a quantile value of the power bins and use that as the estimated noise floor. The quantile should be less than the maximum spectral occupancy of the speech. For example if the speech never fills more than 50% of the spectrum then the median (quantile 0.5) might be reasonable. If the speech fills more than half the spectrum then use a smaller quantile.