A modern hearing aid should be aesthetically appealing as well as offer sufficient and adequate signal amplification. Due to the small physical size of these devices, acoustical feedback (howling) is a major problem. Apart from the annoyance and potential hearing damaging effects that howling implies, it also reduces the supplied maximum Real Ear Aided Gain (REAG). This paper proposes a novel method for subband feedback detection and cancellation, based on the zero-crossing rate measure. After splitting the hearing aid input signal into subbands, the distances between subband zero-crossings are measured. A low distance variance in a particular subband indicates that howling has arisen. The variance measure is then used to adaptively and continuously steer subband gain functions which attenuate tonal infested subbands. The method has proven to be robust and simulation indicates that it offers additional REAG of about 15 dB.
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