1. A method comprising: characterizing, by a computing device, a speech input based on a dynamic noise adaptation (DNA) model reflecting effects of background noise; characterizing the speech input based on a null noise DNA model reflecting a null noise mismatch condition; and performing Bayesian model selection and re-weighting of the DNA model and the null noise DNA model to realize a modified DNA model characterizing the speech input for automatic speech recognition and compensating for noise to a varying degree depending on relative probabilities of the DNA model and the null noise DNA model.