Noise-induced change of tone dispersion in Cantonese speech

Abstract

Noise effect on speaking non-tonal languages is reported on acoustic correlates including increased intensity, enlarged vowel space and raised fundamental frequency. Adverse influence may also be present in realization of tones, which however remains under-explored. Tone-space size and the according tone dispersion offer key indicators to the nature of a tonal system. The present study investigates whether and how Cantonese tones are modified in speaking under noise. Adult native speakers of Cantonese read tri-syllabic words embedded in carrier sentences in quiet and under multi-talker babbles. The speech materials cover six tones (T55, T25, T33, T21, T23, T22) and are balanced between high-low and low-high tone combinations to avoid biased articulatory effects. Results confirm Lombard speech effect in Cantonese speaking. Moreover, under the noise condition, tone spaces of all six tones are enlarged and tones are more dispersed, especially in realization of T55 and T21 that mark the upper and lower ranges of the tonal space. Changes in tone production by female speakers are more significant than those in male speech. This study provides new evidence of phonetic accommodation under noise and in particular noise effects on sizes of tone space, which is not found in the production of monosyllabic words in Cantonese. Our speakers may have used labored speech production to compensate for signal degradation under babble noise, leading to higher dispersion of tones than clear speech in quiet.