Abstract
In human hearing, frequency resolution is a term used to determine how well the ear can separate and distinguish two sounds that are close in frequency. This capability of breaking speech sounds into various frequency components plays a key role in processing and understanding speech information. In this paper, a piecewise-linear frequency shifting algorithm for digital hearing aids is proposed. The algorithm specifically aims at improving the frequency resolution capability. In the first step, frequency discrimination thresholds are processed by a computer testing software. Then, the input signal is parsed through the proposed piecewise-linear frequency shifting algorithm, which comprises of linearly stretching and compressing the frequency content at different frequency ranges. Experimental results showed that by using the proposed frequency shifting algorithm, the separation of formant tracks was increased in the stretching region and slightly squeezed in the adjacent compression region. Subjective assessment on six hearing-impaired persons with V-shaped audiograms demonstrated that nearly a 10% improvement of speech discrimination score was achieved for monosyllabic word lists tested in a quiet acoustic setting. In addition, the speech reception threshold was also improved by 2~8 dB when disyllabic word listswere tested in a noisy acoustic scenario.
Highlights
Signal processing research in digital hearing aids is mainly focused on improving “audibility” of acoustic signals, which is typically attempted to achieve loudness compensation and dynamic range compression of input sound in different frequency and sound pressure levels
These methods essentially are aimed to achieve a certain intensity of output sound in the digital hearing aids which will fit the characteristics of hearing-impaired patients
In Chinese, energy of the voiceless consonant is mainly focused on the medium-high frequency range
Summary
Signal processing research in digital hearing aids is mainly focused on improving “audibility” of acoustic signals, which is typically attempted to achieve loudness compensation and dynamic range compression of input sound in different frequency and sound pressure levels. A frequency-lowering algorithm which moves high frequency components of the input audio signals into lower frequency regions was proposed in [10,11] By using this algorithm, the severely hearing-impaired persons can perceive the previously lost high frequency components sounds as they have been shifted into a lower frequency range that is audible for the patients. Different from the previous SCE algorithm, the proposed scheme is to improve the frequency resolution not by changing the peak-valley difference of the amplitude spectrum, but by executing piecewise-linear frequency shift of the input signals. Experimental results indicated that the proposed piecewise-linear frequency shifting algorithm effectively improved the speech discrimination scores and decreased the speech reception thresholds of the tested subjects.
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