10. One or more non-transitory computer-readable media storing executable instructions that, when executed by a processor, cause a device to: receive a sequence of speech features that characterize an unknown speech input, the sequence of speech features including speech portions and non-speech portions; determine, using voice activity detection (VAD), the speech portions of the sequence of speech features; determine a mean C 0 value for the sequence of speech features, wherein C 0 comprises an average log-energy of a given speech frame of the sequence of speech features, normalize selected speech features of the sequence of speech features using a plurality of different feature normalizing functions including a first function used only for the speech portions and a second function used only for the non-speech portions, wherein the first function normalizes the C 0 by subtracting a max C 0 that is estimated at a start of an utterance including the given speech frame and subsequently updated throughout the utterance; and combine the normalized selected speech features to produce a sequence of mixed normalized speech features for automatic speech recognition of the speech portions of the sequence of speech features.
15. The non-transitory computer-readable media of claim 10 , wherein the selected speech features comprise a speech energy feature and at least one feature normalizing function of the plurality of different feature normalizing functions normalizes the speech energy feature.