9. A tangible computer-readable storage memory having program instructions stored thereon that, upon execution by a computer system, cause the computer system to: store a non-negative hidden Markov model (N-HMM) corresponding to a sound source, the N-HMM model being based, at least in part, on a training signal emitted by the sound source; in response to receiving an instruction to separate sounds within a mixed signal, the mixed signal including a first sound emitted by the sound source and one or more other sounds emitted by one or more other sources, generate a non-negative factorial hidden Markov model (NFHMM) model for the mixed signal based, at least in part, on the N-HMM model, the N-FHMM being generated in the absence of a training signal emitted by the one or more other sources; construct a filter based, at least in part, on the N-FHMM model; and apply the filter in time and frequency as a spectrogram to the mixed signal to separate the first sound from the one or more other sounds.
9. A tangible computer-readable storage memory having program instructions stored thereon that, upon execution by a computer system, cause the computer system to: store a non-negative hidden Markov model (N-HMM) corresponding to a sound source, the N-HMM model being based, at least in part, on a training signal emitted by the sound source; in response to receiving an instruction to separate sounds within a mixed signal, the mixed signal including a first sound emitted by the sound source and one or more other sounds emitted by one or more other sources, generate a non-negative factorial hidden Markov model (NFHMM) model for the mixed signal based, at least in part, on the N-HMM model, the N-FHMM being generated in the absence of a training signal emitted by the one or more other sources; construct a filter based, at least in part, on the N-FHMM model; and apply the filter in time and frequency as a spectrogram to the mixed signal to separate the first sound from the one or more other sounds. 13. The tangible computer-readable storage memory of claim 9 , wherein the first sound includes speech and the one or more other sounds include noise.