1. A method of restoring an audio signal, the method comprising: inputting an audio signal for restoration; determining a mask defining desired and undesired regions of a time-frequency spectrum of said audio signal, wherein said mask is represented by mask data; determining estimated values for a set of latent variables, a product of said latent variables and said mask factorizing a tensor representation of a set of property values of said input audio signal; wherein said input audio signal is modeled as a set of audio source components comprising one or more desired audio source components and one or more undesired audio source components, and wherein said tensor representation of said property values comprises a combination of desired property values for said desired audio source components and undesired property values for said undesired audio source components; and reconstructing a restored version of said audio signal from said desired property values of said desired source components; wherein said set of property values of said input audio signal comprises a set of variance or covariance values comprising a combination of desired variance or covariance values for said desired audio source components and undesired variance or covariance values for said undesired audio source components; and wherein said reconstructing uses said desired variance or covariance values to reconstruct said restored version of said audio signal.