Influence of Speech Recognition Ability on Acceptable Noise Level for Mandarin (Chinese) Speakers with Normal Hearing.

Introduction: Noise can induce hearing loss and reduce speech understanding. The Acceptable Noise Level (ANL) test has been widely used in audiology. However, strategies used by listeners to determine ANLs are unclear. The current study evaluated the role of speech recognition in selecting ANL and how well ANL could predict speech understanding in a noisy situation.

Methods: Forty-five Mandarin speakers with normal hearing were tested in both ears. ANL is defined as Most Comfortable Level (MCL) minus Background Noise Level (BNL). To obtain ANL monaurally with an earphone, the study measured participants' MCL to hear a Mandarin story in quiet and the maximum BNL to tolerate while following the story. Then, based on the participant's ANL, speech recognition in noise was examined using a set of phonemic-balanced Mandarin words. The signal-to-noise ratio (SNR) was adjusted to ANL, ANL - 10 dB ("degraded noise condition"), and ANL + 10 dB ("improved noise condition").

Results: The mean ANLs were 2.4 dB and 2.6 dB for the left and right ears, respectively. The mean speech recognition with SNR adjusted to ANL was relatively high for both ears (81-83% correct). Even for those ear samples with very low ANL (<0 dB), speech performance obtained at SNR = ANL was still high. The mean speech recognition obtained at SNR = ANL was 5 percentage points lower than the mean speech recognition at the improved noise condition and 14 percentage points higher than the mean speech recognition at the degraded noise condition. Speech recognition obtained at SNR = ANL and ANL - 10 dB correlated significantly with ANL.

Conclusion: Speech recognition in noise appears to play an important role for listeners with normal hearing in deciding their ANLs. Additionally, ANL can predict speech performance (r-squared = 53-61%) in the degraded noise condition.