24. A speech recognition system, comprising: a sound classifier that includes at least one non-transitory processor-readable medium and at least one processor communicatively coupled to the at least one non-transitory processor-readable medium, and that analyzes each of a plurality of frames of audio, classifies a first number of the frames of audio as speech by the sound classifier, classifies a second number of the frames of audio as non-transient background noise by the sound classifier, classifies a third number of the frames of audio as transient noise events by the sound classifier, and provides signals indicative at least of the classifications of the frames of audio.
38. The speech recognition system of claim 24 wherein at least one component of the voice recognition system updates a background noise estimate based on non-transient background noise and not based on transient noise events or speech events.