1. Field of the Invention
The invention generally relates to noise suppression.
2. Background
Electronic voice communication via communication devices such as cellular telephones, personal digital assistants, etc. is becoming common in an ever increasing range of environments. Such environments often are characterized by non-stationary noise. Conventional noise suppression techniques typically are not capable of suppressing such non-stationary noise. For instance, conventional single channel noise suppression techniques such as spectral subtraction and Wiener filtering rely on stationarity of the noise in order to estimate it and therefore typically are restricted to handling stationary or quasi-stationary noise in practice.
Single-channel nonnegative matrix factorization (SNMF) is one exemplary technique that has been proposed for suppressing non-stationary noise. SNMF is based on a matrix equation that may be represented as V≈WH. A locally optimal choice of W and H are determined to solve the matrix equation for nonnegative V, W, and H. The signal, V, is a spectrogram. W is a set of specific spectral shapes or basis vectors (a.k.a. building blocks) that define a model of an audio source. H is a set of time-varying activation levels of the respective building blocks.
However, SNMF has limitations. For instance, SNMF relies upon noise information (noise modeling) as a priori knowledge, which limits its application in practice as the noise environment changes. Such changes in the noise environment typically are not known or predictable before the SNMF technique is performed.