Understanding the Lombard Effect for Mandarin: Relation Between Speech Recognition Thresholds and Acoustic Parameters.

The present work quantifies the Lombard effect across native speakers of Mandarin Chinese using the Matrix sentence test, which is optimized for precisely assessing speech recognition thresholds (SRTs) in noise. Specifically, we studied the effects of speaker gender, fundamental frequency (F0), formant frequencies (F1 and F2), the duration and rate of voiced segments, and frequency-specific energy redistribution characterized by alpha ratio and speech-weighted signal-to-noise ratio (swSNR) on the recognition of Mandarin in plain and Lombard speech. The Mandarin Chinese matrix test was recorded with plain and Lombard speech from 11 native-Mandarin speakers. SRTs in stationary noise were measured with native-Mandarin, normal-hearing listeners. Results showed that on average, Mandarin Lombard speech was more intelligible than Mandarin plain speech for both female and male speakers, and the Mandarin Lombard gain of female speakers was larger than that of males. In addition, various acoustic analyses involving all speakers showed that (a) only swSNR was significantly correlated with the SRT of the Mandarin plain speech; (b) most acoustic measures were significantly correlated with the SRT of the Mandarin Lombard speech; and (c) alpha ratio and swSNR were significantly correlated with the SRT Lombard gain. In addition, a gender effect was found in the correlational analysis between acoustic parameters and SRT as well as Lombard gain in SRT. The findings highlight the impact of increased high-frequency energy on the observed Lombard gain in Mandarin speech, whereas the changes in individual acoustic parameters (e.g., F0 and F1) appear to play only a minor role.