W. Van Summers

Effects of noise on speech production: Acoustic and perceptual analyses

Acoustical analyses were carried out on a set of utterances produced by two male speakers talking in quiet and in 80, 90, and 100 dB SPL of masking noise. In addition to replicating previous studies demonstrating increases in amplitude, duration, and vocal pitch while talking in noise, these analyses also found reliable differences in the formant frequencies and short-term spectra of vowels. Perceptual experiments were also conducted to assess the intelligibility of utterances produced in quiet and in noise when they were presented at equal S/N ratios for identification. In each experiment, utterances originally produced in noise were found to be more intelligible than utterances produced in the quiet. The results of the acoustic analyses showed clear and consistent differences in the acoustic-phonetic characteristics of speech produced in quiet versus noisy environments. Moreover, these accounts differences produced reliable effects on intelligibility. The findings are discussed in terms of: (1) the nature of the acoustic changes that taken place when speakers produce speech under adverse conditions such as noise, psychological stress, or high cognitive load: (2) the role of training and feedback in controlling and modifying a talkers speech to improve performance of current speech recognizers; and (3) the development of robust algorithms for recognition of speech in noise.

Effects of stress and final‐consonant voicing on vowel production: Articulatory and acoustic analyses

Durations of the vocalic portions of speech are influenced by a large number of linguistic and nonlinguistic factors (e.g., stress and speaking rate). However, each factor affecting vowel duration may influence articulation in a unique manner. The present study examined the effects of stress and final-consonant voicing on the detailed structure of articulatory and acoustic patterns in consonant-vowel-consonant (CVC) utterances. Jaw movement trajectories and F 1 trajectories were examined for a corpus of utterances differing in stress and final-consonant voicing. Jaw lowering and raising gestures were more rapid, longer in duration, and spatially more extensive for stressed versus unstressed utterances. At the acoustic level, stressed utterances showed more rapid initial F 1 transitions and more extreme F 1 steady-state frequencies than unstressed utterances. In contrast to the results obtained in the analysis of stress, decreases in vowel duration due to devoicing did not result in a reduction in the velocity or spatial extent of the articulatory gestures. Similarly, at the acoustic level, the reductions in formant transition slopes and steady-state frequencies demonstrated by the shorter, unstressed utterances did not occur for the shorter, voiceless utterances. The results demonstrate that stress-related and voicing-related changes in vowel duration are accomplished by separate and distinct changes in speech production with observable consequences at both the articulatory and acoustic levels.

Vowel length and closure duration in word‐medial VC sequences

Previous research has shown that English vowel length varies depending on the voicing characteristic of the following consonant. For stop consonants, closure durations also vary as a function of consonantal voicing. Generally, vowel‐stop sequences containing voiced consonants show longer vowel durations and shorter closure durations than similar sequences containing voiceless consonants. These previous studies have focused on stressed vowels in monosyllabic or bisyllabic words. Very little research has examined the effects of postvocalic voicing on stressless vowels. In the present study, the influence of postvocalic voicing on vowel and closure durations in VCV and VCV sequences is studied. Subjects produced sentence pairs containing target words contrasting in intervocalic consonantal voicing (e.g., adopt‐atop, tabbing‐tapping). Both stressed and unstressed vowels tended to lengthen before voiced consonants. However, the vowel‐lengthening effect was not as consistent for stressless vowels as for stres...

An addendum to ‘‘Effects of noise on speech production: Acoustic and perceptual analyses’’ [J. Acoust. Soc. Am. 84, 917–928 (1988)]

The authors respond to Fitchs comments [H. Fitch, J. Acoust. Soc. Am. 86, 2017-2019 (1989)] on an earlier paper. New analyses are presented to address the question of whether F1 differences observed in the original report are an artifact of linear predictive coding (LPC) analysis techniques. Contrary to Fitchs claims, the results suggest that the F1 differences originally reported are, in fact, due to changes in vocal tract resonance characteristics. It is concluded that there are important acoustic-phonetic differences in speech when talkers speak in noise. These differences reflect changes in both glottal and supraglottal events that are designed to maintain speech intelligibility under adverse conditions.

The internal signal‐to‐noise ratio in hearing‐impaired listeners

The reduced frequency resolution often demonstrated by listeners with sensorineural hearing impairment might have at least two related effects on their perception of speech in background noise. The internal representation of the peaks and valleys in the speech spectrum become smeared, resulting in less precise frequency analysis than can be achieved by normal‐hearing persons. In addition, when the speech is embedded in noise, poorer frequency resolution will, in theory, result in a greater‐than‐normal decrease in the signal‐to‐noise ratio at the outputs of the auditory filters. This poorer‐than‐normal internal S/N might account for the common observation that noise is more degrading to speech understanding by hearing‐impaired listeners than by normal‐hearing listeners. To assess the validity of this notion, both normal‐hearing and hearing‐impaired subjects participated in an identification experiment using highly simplified vowel‐like harmonic complexes presented in quiet and in three levels of broadband ...

Effects of cognitive workload on speech production

Previous research on the acoustic properties of speech has generally focused on “normal” speech produced under benign conditions. Typically, subjects produce utterances in a quiet laboratory setting with no competing or distracting stimuli present. Almost no basic research has examined speech in more demanding environments. For example, pilots may often be required to produce speech while simultaneously performing several other attention‐demanding tasks. The information‐processing requirements of these simultaneous tasks may affect the acoustic properties of speech in a wide variety of ways. The present research examined speech produced under benign conditions and while simultaneously performing an attention‐demanding perceptual‐motor task. Speech produced while carrying out the perceptual‐motor task showed reliable increases in amplitude and fundamental frequency and reductions in segmental durations and spectral tilt. The results have implications for automatic speech recognition in demanding environmen...