We present an algorithm for removing time-frequency components, found by a standard Gabor transform, of a ldquoreal-worldrdquo sound while causing no audible difference to the original sound after resynthesis. Thus, this representation is made sparser. The selection of removable components is based on a simple model of simultaneous masking in the auditory system. Important goals were the applicability to any real-world music and speech sound, integrating mutual masking effects between time-frequency components, coping with the time-frequency spread of such an operation, and computational efficiency. The proposed algorithm first determines an estimation of the masked threshold within an analysis window. The masked threshold function is then shifted in level by an amount determined experimentally, and all components falling below this function (the irrelevance threshold) are removed. This shift gives a conservative way to deal with uncertainty effects resulting from removing time-frequency components and with inaccuracies in the masking model. The removal of components is described as an adaptive Gabor multiplier. Thirty-six normal hearing subjects participated in an experiment to determine the maximum shift value for which they could not discriminate the irrelevance filtered signal from the original signal. On average across the test stimuli, 32 percent of the time-frequency components fell below the irrelevance threshold.

The author reports on the LISTEN project, a research project funded by the European Commission in the context of the Information Society Technology (IST) program. LISTEN, which started in January 2001, will provide users with intuitive access to personalized and situated audio information spaces while they naturally explore everyday environments. A new form of multisensory content is proposed to enhance the sensual impact of a broad spectrum of applications ranging from art installations to entertainment events. This is achieved by augmenting the physical environment through a dynamic soundscape, which users experience over motion-tracked wireless headphones. Immersive audio-augmented environments are created by combining high-definition spatial audio rendering technology with advanced user modeling methods. These allow for adapting the content to the users' individual spatial behavior. The project will produce several prototypes and a virtual reality based authoring tool. Technological innovations will be validated under laboratory conditions, whilst the prototypes will be evaluated in public exhibitions.