30. The computer-readable medium of claim 21 , wherein classifying the portion at the second classifier as speech or as music comprises determining if there is any signal activity in the portion, and if there is no signal activity, then determining that there is no useful signal to encode, and encoding the portion as speech.
21. A non-transitory computer-readable medium comprising computer-readable instructions for causing a processor to: receive a portion of an audio signal at a first classifier in a digital audio device; classify, by the digital audio device, the portion of the audio signal at the first classifier as speech or as music; and process the portion of the audio signal, wherein processing the portion of the audio signal comprises: if the portion is classified by the first classifier as speech, then encode, by the digital audio device, the speech using a first coding mode; or if the portion is classified by the first classifier as music, then: provide the portion to a second classifier in the digital audio device; classify, by the digital audio device, the portion at the second classifier as speech or as music; and encode the portion of the audio signal, wherein encoding the portion of the audio signal comprises: if the portion is classified at the second classifier as speech, then encode, by the digital audio device, the portion using a second coding mode; or if the portion is classified at the second classifier as music, then encode, by the digital audio device, the portion using a third coding mode.