Undergraduate Honors Theses

Thesis Defended

Spring 2011

Document Type



Speech, Language & Hearing Sciences

First Advisor

Katheryn Arehard


Objectives: The purpose of this study was to determine if Acceptable Noise Levels (ANL) are related to subjective quality ratings at varying signal-to-noise ratios (SNR) in normal- hearing individuals. Design: The study included 13 adult listeners with normal hearing who participated in two tasks. The first task was the ANL test that was administered with the standard clinical protocol established by Nabelek (2004). The second task was rating sound quality using five different scales (overall, loudness, pleasantness, background noise, and clarity) in the presence of varying SNRs (-10 dB SNR, 0 dB SNR, 10 dB SNR, 20 dB SNR, and 30 dB SNR). Results: The ANL scores ranged from -4 dB SNR to 17 dB SNR, with an average of 3.5 dB SNR and a standard deviation of 5.2 dB. Quality ratings varied significantly as a function of SNR, but the effects of SNR did not differ significantly across scale. ANL scores were significantly correlated for pleasantness at 10, 20, and 30 dB SNR, for clarity 10 and 20 dB SNR, and for background noise 20 dB SNR. Results were also considered in terms of the values of listeners’ quality ratings at the dB SNR corresponding to the ANL. On average, the quality ratings that occurred at the dB SNR corresponding to the ANL were a 3.7 on the overall scale (with 10 being the best), a 3.7 on the clarity scale (with 10 being the clearest), a 3.8 on the pleasantness scale (with 10 being the most pleasant), a 5.5 on the loudness scale (with 10 being the loudest), and a 6.2 on the background noise scale (with 10 being noisiest). Conclusions: The data revealed two main relationships. First, ANL is significantly correlated to sound quality for several scales (pleasantness, clarity, and background noise) for SNRs at 10 dB and above. Second, noise tolerance, as measured by the ANL, is associated with sound quality perception in the following way: when sounds are at SNRs that are at or above a listener’s ANL, the quality rating will be at least a 6 (on a 10 point scale)..