Krause Jean C, Braida Louis D
Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
J Acoust Soc Am. 2004 Jan;115(1):362-78. doi: 10.1121/1.1635842.
Sentences spoken "clearly" are significantly more intelligible than those spoken "conversationally" for hearing-impaired listeners in a variety of backgrounds [Picheny et al., J. Speech Hear. Res. 28, 96-103 (1985); Uchanski et al., ibid. 39, 494-509 (1996); Payton et al., J. Acoust. Soc. Am. 95, 1581-1592 (1994)]. While producing clear speech, however, talkers often reduce their speaking rate significantly [Picheny et al., J. Speech Hear. Res. 29, 434-446 (1986); Uchanski et al., ibid. 39, 494-509 (1996)]. Yet speaking slowly is not solely responsible for the intelligibility benefit of clear speech (over conversational speech), since a recent study [Krause and Braida, J. Acoust. Soc. Am. 112, 2165-2172 (2002)] showed that talkers can produce clear speech at normal rates with training. This finding suggests that clear speech has inherent acoustic properties, independent of rate, that contribute to improved intelligibility. Identifying these acoustic properties could lead to improved signal processing schemes for hearing aids. To gain insight into these acoustical properties, conversational and clear speech produced at normal speaking rates were analyzed at three levels of detail (global, phonological, and phonetic). Although results suggest that talkers may have employed different strategies to achieve clear speech at normal rates, two global-level properties were identified that appear likely to be linked to the improvements in intelligibility provided by clear/normal speech: increased energy in the 1000-3000-Hz range of long-term spectra and increased modulation depth of low frequency modulations of the intensity envelope. Other phonological and phonetic differences associated with clear/normal speech include changes in (1) frequency of stop burst releases, (2) VOT of word-initial voiceless stop consonants, and (3) short-term vowel spectra.
对于各种背景下的听力受损听众而言，“清晰”说出的句子比“随意交谈式”说出的句子明显更易懂[皮切尼等人，《言语与听觉研究杂志》28卷，96 - 103页（1985年）；乌钱斯基等人，同刊39卷，494 - 509页（1996年）；佩顿等人，《美国声学学会杂志》95卷，1581 - 1592页（1994年）]。然而，在产生清晰言语时，说话者往往会显著降低语速[皮切尼等人，《言语与听觉研究杂志》29卷，434 - 446页（1986年）；乌钱斯基等人，同刊39卷，494 - 509页（1996年）]。不过，语速慢并非清晰言语（相对于随意交谈言语）易懂性提升的唯一原因，因为最近一项研究[克劳斯和布拉伊达，《美国声学学会杂志》112卷，2165 - 2172页（2002年）]表明，通过训练，说话者能够以正常语速说出清晰言语。这一发现表明，清晰言语具有独立于语速的固有声学特性，这些特性有助于提高可懂度。识别这些声学特性可能会带来改进的助听器信号处理方案。为深入了解这些声学特性，对以正常语速产生的随意交谈言语和清晰言语在三个细节层面（全局、音系和语音层面）进行了分析。尽管结果表明，说话者可能采用了不同策略来以正常语速实现清晰言语，但确定了两个全局层面的特性，它们似乎可能与清晰/正常言语所带来的可懂度提升相关：长期频谱中1000 - 3000赫兹范围内能量增加以及强度包络低频调制的调制深度增加。与清晰/正常言语相关的其他音系和语音差异包括：（1）塞音爆破释放频率的变化，（2）单词起始清塞音的VOT，以及（3）短期元音频谱的变化。
