1. A noise reduction system including an audio-visual user interface therein for combining visual features extracted from a digital video sequence with audio features extracted from an analog audio sequence including background noise in an environment of a speaker, said noise reduction system comprising: an audio sequence detection device for detecting said analog audio sequence; an audio feature extraction and analysis device for analyzing said analog audio sequence and extracting said audio features therefrom; a video sequence detection device for detecting said video sequence; a visual feature extraction and analysis device for analyzing the detected video sequence and extracting said visual features therefrom; a noise reduction circuit configured to separate a speaker's voice from said background noise based on a combination of derived speech characteristics by removing said separated background noise from said analog audio sequence and configured to output a speech activity indication signal comprising a combination of speech activity estimates supplied by said audio feature extraction and analysis device and said visual feature extraction and analysis device; and a multi-channel acoustic echo cancellation unit configured to perform a near-end speaker detection and double-talk detection algorithm based on the speech characteristics derived by said audio feature extraction and analysis device and said visual feature extraction and analysis device, wherein said noise reduction circuit is further configured to subtract a discretized version of an estimated noise power density spectrum of said background noise from a discrete signal spectrum of an analog-to-digital converted version of said analog audio sequence, said estimated noise power density spectrum being based on said audio features, said visual features and said discrete signal spectrum.