1. A computer-implemented method employing at least one hardware implemented computer processor for performing cepstral mean normalization (CMN) in automatic speech recognition comprising: storing a current CMN function in a computer memory as a previous CMN function; updating the current CMN function based on a current audio input to produce an updated CMN function; using the updated CMN function to process the current audio input to produce a processed audio input; attempting to perform automatic speech recognition of the processed audio input to determine representative text; if the processed audio input is not recognized as representative text, replacing the updated CMN function with the previous CMN function.