Voice quality influences acceptable noise levels in adults with normal hearing and hearing loss: introducing the signal degradation degree

OBJECTIVE: The study aimed to measure the effect of speaker voice quality on acceptable noise level (ANL) and to introduce the Signal Degradation Degree (SDD) to quantify within-listener sensitivity to voice-related signal degradation. DESIGN: The participants listened to five voice quality conditions that ranked from the highest-ranked to the lowest-ranked voice quality. The SDD, the difference between the ANL when the voice was of the highest-ranked (Q1) and the lowest-ranked voice quality (Q4), was calculated. STUDY SAMPLE: Sixty-seven adults with normal hearing (NH) and thirty-five with hearing loss (HL) participated. RESULTS: As the voice quality deteriorated, there was a significant increase in the ANL for both groups, which demonstrated a reduction in their ability to tolerate noise. Compared to HLs, the NHs were found to have greater ANL and SDD with each decrease in voice quality, indicating that the NH adults were much more sensitive to decreases in speech clarity than the HL adults. CONCLUSIONS: Voice quality is an intrinsic speech signal factor that influences ANL in both NH and HL listeners. As perceived voice quality declined, tolerance for background noise decreased. SDD may complement ANL by quantifying how much an individual listener's noise tolerance changes when target speech quality deteriorates; however, its clinical utility, reliability, and predictive value require further validation against speech-in-noise performance, hearing aid benefit, and real-world communication outcomes.