Amplitude compression method for a digital hearing aid using a composite filter

Abstract

As an amplitude compression method effective for sensory hearing impairment, a new method is proposed in which a composite filter to be operated in real time on DSP is used in order to reduce the audible distortion of compressed speech appearing in the conventional multiband compression. In this paper, a generation method is described for a composite compression filter based on broad-band compression preserving the spectral shape. It is shown that this filter can be realized with reduced operational complexity in comparison with the conventional frequency sampling filter design. By means of an auditory evaluation experiment employing normal hearing listeners and hearing-impaired listeners, the effect of distortion reduction in compressed sounds was confirmed. Further, an adaptive band-level estimation is discussed to cope with the contradicting dynamic compression characteristics between instantaneous compression and syllabic compression.