Viennatone Ges. M.B.H., Frobelgasse 26-32, A-1164 Vienna, Austria
A signal processing scheme is proposed to improve speech quality for the hearing-impaired people (HI). In this scheme, Hilbert transform and vector sum generator are used to obtain the Hilbert envelope AM, and it follows a voltage-controlled amplifier (VCA) with the gain inversely proportional to AM, the output signal of VCA is sent to a modulator. On the other hand, AM is dynamically processed by a lowpass filter and nonlinear amplitude processor, then sent to the said modulator to restore the dynamic range of the speech. In comparison with the original speech, the resulting one is of a little spectral enhancement, the intermodulation-distortion (ID), and some compression effect because of the nonlinear amplitude processing. Towards the end of our research, the informal listening experiment was performed, 25 people with sensorineural hearing impairment who wear their own hearing aids routinely participated in the experiment. The experiment results have shown that 80% listeners preferred the processed speech to the original one. This result is quite consistent with one of our expectations: HIs lose the nonlinear active characteristics to some extent, therefore, introducing appropriately ID can help HIs to perceive speech.