Noise reduction in hearing aids: a case for wavelet-based methods

This study reviews the development of a new wavelet-based, single-microphone noise reduction algorithm for use in digital hearing aids. The approach reduces noise by expanding the observed speech in a series of implicitly filtered, shift-invariant wavelet packet basis vectors. Recordings of speech in automobile road noise at signal-to-noise ratios (SNRs) ranging from 0 to 20 dB were used to evaluate the new method. Objective measurements indicate that the new method provides better noise reduction and lower signal distortion than previous wavelet-based methods, and produces output free from the audible artifacts of a conventional FFT-based method. Trials of the Revised SPIN test conducted with two groups of hearing-impaired subjects indicate that the new algorithm can improve speech intelligibility for flat-loss subjects in a simulated hearing-aid application