Notch-filter-based howling suppression (NHS) is one of the most popular methods for acoustic feedback control in public address and hands-free communication systems. The NHS method consists of two stages: howling detection and notch filter design. While the design of notch filters is based on well-established filter design techniques, there is little agreement in the NHS literature on how the howling detection subproblem should be tackled. Moreover, since the NHS literature mainly consists of patents, only few experimental results have been reported. The aim of this paper is to describe a unifying framework for howling detection, and to provide a comparative evaluation of existing and novel howling detection criteria.
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