Shigekiyo Fujii

The design and evaluation of a noise suppression system for custom‐made digital hearing aids

A noise suppression system, which has the inbuilt feature to adapt to the local environment, for custom‐made digital hearing aids has been developed. The signal process is based on spectral subtraction technology with 32 bands in the frequency domain. The signal‐to‐noise ratio was improved by an average of 7.5 dB in rms level. Its effectiveness was evaluated using the seven‐point rating scale method for nine normal‐hearing subjects and six hearing impaired subjects. Test speech is presented under three different environments, which consist of a car, a duct, and a crowded place. As a result of the assessment, the same tendency is observed between normal and hearing‐impaired subjects and there were two good points that were found. First, the noise suppression system makes them more comfortable to listen to speech with the statistical significance of p=0.05. Second, the noisiness is reduced with the statistical significance of p=0.01. It should be noted that there is a scattering of the plotted data; however...