Relationship between Envelope Difference Index, Sentence Recognition and Speech Quality in Individuals with Hearing Impairment

Abstract

The speech signal consists of temporal envelope and temporal fine structure. Studies have reported of alterations in the envelope of the signal when processed through different digital signal processing (DSP) algorithms in the hearing aid. Hence, the present study aimed at investigating the combined effects of the DSP algorithms used in digital hearing aids on speech recognition scores (SRS), quality perception of speech and envelope difference index (EDI), and to assess the correlation between the subjective and the objective measures. A total of 25 individuals with mild to moderate sensorineural hearing loss in the age range of 18-55 years were included in the study. Experiments were carried out to measure SRS, quality perception and EDI in the unaided condition, in linear mode (all algorithms deactivated) and nonlinear mode (all algorithms activated) at 55 dB SPL, 65 dB SPL and 80 dB SPL. The testing was done in quiet and at +10 dB SNR using speech shaped noise. The results revealed that the SRS and the quality ratings were significantly better at higher presentation level and in linear mode in quiet. However, the EDI was very similar across different aided conditions. The correlation obtained between the objective and the subjective measures was limited to few test conditions with only a moderate level of correlation. Hence, it is clear that, an insignificant change in the temporal envelope of the signal can also lead to a significant change in the perception of speech. That is, the DSP algorithms brought about negative changes in the output as reflected in the SRS, quality perception and subjective preference.