Nao Hodoshima

Modulation enhancement of speech by a pre-processing algorithm for improving intelligibility in reverberant environments

Most listeners have difficulty understanding speech in reverberant conditions. The purpose of this study is to investigate whether it is possible to reduce the degree of degradation of speech intelligibility in reverberation through the development of an algorithm. The modulation spectrum is the spectral representation of the temporal envelope of the speech signal. That of clean speech is dominated by components between 1 and 16 Hz centered at 4 Hz which is the most important range for human perception of speech. In reverberant conditions, the modulation spectrum of speech is shifted toward the lower end of the modulation frequency range. In this study, we proposed to enhance the important modulation spectral components prior to distortion of speech by reverberation. Word intelligibility in a carrier sentence was tested with the newly developed algorithm including two different filter designs in three reverberant conditions. The reverberant speech was simulated by convoluting clean speech with impulse responses measured in the actual halls. The experimental results show that modulation filtering incorporated into a pre-processing algorithm improves intelligibility for normal hearing listeners when (1) the modulation filters are optimal for a specific reverberant condition (i.e., T60 = 1.1 s), and (2) consonants are preceded by highly powered segments. Under shorter (0.7 s) and longer (1.6 s) reverberation times, the modulation filtering in the current experiments, an Empirically-Designed (ED) filter and a Data-Derived (D-D) filter, caused a slight performance decrement respectively. The results of this study suggest that further gains in intelligibility may be accomplished by re-design of the modulation filters suitable for other reverberant conditions. � 2004 Elsevier B.V. All rights reserved.

Improving syllable identification by a preprocessing method reducing overlap-masking in reverberant environments

Overlap-masking degrades speech intelligibility in reverberation [R. H. Bolt and A. D. MacDonald, J. Acoust. Soc. Am. 21(6), 577-580 (1949)]. To reduce the effect of this degradation, steady-state suppression has been proposed as a preprocessing technique [Arai et al., Proc. Autumn Meet. Acoust. Soc. Jpn., 2001; Acoust. Sci. Tech. 23(8), 229-232 (2002)]. This technique automatically suppresses steady-state portions of speech that have more energy but are less crucial for speech perception. The present paper explores the effect of steady-state suppression on syllable identification preceded by /a/ under various reverberant conditions. In each of two perception experiments, stimuli were presented to 22 subjects with normal hearing. The stimuli consisted of mono-syllables in a carrier phrase with and without steady-state suppression and were presented under different reverberant conditions using artificial impulse responses. The results indicate that steady-state suppression statistically improves consonant identification for reverberation times of 0.7 to 1.2 s. Analysis of confusion matrices shows that identification of voiced consonants, stop and nasal consonants, and bilabial, alveolar, and velar consonants were especially improved by steady-state suppression. The steady-state suppression is demonstrated to be an effective preprocessing method for improving syllable identification by reducing the effect of overlap-masking under specific reverberant conditions.

Using Steady-State Suppression to Improve Speech Intelligibility in Reverberant Environments for Elderly Listeners

Reverberation is a large problem for speech communication and it is known that strong reverberation affects speech intelligibility. This is especially true for people with hearing impairments and/or elderly people. Several approaches have been proposed and discussed to improve speech intelligibility degraded by reverberation. Steady-state suppression is one such approach, in which speech signals are processed before being radiated through the loudspeakers of a public address system to reduce overlap masking, which is one of the major causes of degradation in speech intelligibility. We investigated whether the steady-state suppression technique improves the intelligibility of speech in reverberant environments for elderly listeners. In both simulated and actual reverberant environments, elderly listeners performed worse than younger listeners. The performance in an actual hall was better than with simulated reverberation, and this was consistent with the results for younger listeners. Although the normal hearing group performed better than the presbycusis group, the steady-state suppression technique improved the intelligibility of speech for elderly listeners as was observed for younger listeners in both simulated and actual reverberant environments.

Effects of Urgent Speech and Preceding Sounds on Speech Intelligibility in Noisy and Reverberant Environments.

Public-address (PA) announcements are used to convey emergency information; however, noise and reverberation sometimes make announcements in public spaces unintelligible. Therefore, the present study investigated how combinations of speech spoken in an urgent style and preceding sounds affect speech intelligibility and perceived urgency in noisy and reverberant environments. Sentences were spoken in normal or urgent styles and preceded by either two sounds (siren sound or ocean wave-like sound) or no sounds. Eighteen young participants carried out word identification test and rated perceived urgency on five-point scales in noisy and reverberant environments. The results showed that the urgently spoken speech had significantly higher speech intelligibility than the normal speech. The urgently spoken speech preceded by the wave-like sound showed significantly higher speech intelligibility than normal speech without sounds, normal speech preceded by the siren sound, and urgently spoken speech preceded by the siren sound. The results also demonstrated that the perceived urgency was rated higher for the urgently spoken speech than that for the normal speech, regardless of the types of preceding sounds. These results suggest that appropriate combinations of speaking styles and alerting sounds will increase the intelligibility of emergency PA announcements.

Investigating an optimum suppression rate of steady‐state portions of speech that improves intelligibility the most as a pre‐processing approach in reverberant environments

Steady‐state suppression has been proposed as a pre‐processing approach to improve speech intelligibility in reverberant environments [Arai et al., Acoust. Sci. Technol. 23, 229–232 (2002)]. The goal of this work is to find the suppression rate that improves intelligibility the most. This is done by exploring the relationship between the suppression rates of steady‐state portions of speech signals in a reverberant environment and syllable identification. This needs to be investigated because the optimum suppression rate might depend on the amount of overlap‐masking, which in turn is determined by the reverberation. A syllable identification test was conducted with 21 normal‐hearing listeners in two reverberant environments and six suppression rates. Results show a significant improvement in intelligibility for a 40% and a 50% suppression rate for a reverberation time of 1.1 s and a 60% suppression rate for a reverberation time of 1.3 s. Findings confirm that intelligibility is affected by both suppression...

Non-native speakers perform poorer than native speakers in Japanese speech recognition in reverberation

Reverberation affects perceptual performance, especially non-native listeners, elderly people, and people with hearing impairments. Native Japanese speakers confused some Japanese consonants and they failed to distinguish Japanese length contrast in reverberation [Arai et al., Proc. Autumn Meet. Acoust. Soc. Jpn., 2016]. The current study examined degradation degree of non-native speakers (native English speakers) in Japanese speech recognition in reverberation, using the same experiment settings with the previous study. There were two sets of stimulus: 1) Japanese consonant-vowel (CV) syllables, 2) non-words varying in duration of a certain vowel/consonant along durational continuum. In the results, although non-native speakers confused consonants even in non-reverberant condition, the number of their confusion in reverberation was larger than that in non-reverberant condition. Confusion of non-native speakers in reverberation was much more than that of native speakers. In addition, the results indicated...

Making speech announcements intelligible in public spaces from a speech production view

Speech announcements in public spaces are often hard to hear due to noise and reverberation, and this is especially true for elderly people compared to young people. This study aims to improve speech intelligibility in noisy/reverberant environments based on the way we change how we speak depending on an acoustic environment. Speech uttered in a noisy environment (noise-induced speech) is generally more intelligible for young people than speech produced in a quiet environment when both types of speech sounds are heard in noise (i.e. Lombard effect). This paper examines whether reverberation- as well as noise-induced speech are more intelligible to young and elderly people. The results of our listening tests showed that elderly listeners had significantly higher word identification scores for noise/reverberation-induced speech than speech spoken in a quiet environment. The results also showed that noise/reverberation-induced speech was more intelligible to the listeners than speech in quiet with background...

Errata to “Using Steady-State Suppression to Improve Speech Intelligibility in Reverberant Environments for Elderly Listeners” [Sep 10 1775-1780]

In the above titled paper (ibid., vol. 18, no. 7, pp. 1775-1780, Sep. 2010), several IPA fonts were displayed incorrectly. The correct fonts are presented here.

Correlation Between a Questionnaire About Noise-Induced Hearing Loss and SPL of Portable Music Players of High School and University Students

The risk of noise-induced hearing loss has been increased for young generations. Several studies pointed out that one reason is listening to digital audio players with a sound pressure level that leads to damage to hearing. This study conducted a questionnaire on 209 high school and university students living in Tokyo about their current situation regarding noise-induced hearing loss. The questionnaire includes the frequency of earphones/headphones usage, noise exposure, self-reported hearing conditions and hearing-related lifestyle. This study also measured A-weighted equivalent sound pressure levels of digital audio players that the students have with normal playback volume. The results showed that more than 90% of the subjects use earphones/headphones, and about 50% use them daily. 58% of the subjects use them while commuting, meaning that they listen to music in noisy trains and buses. 16% of the subjects reported that they have experienced hearing problems such as tinnitus symptoms and listening difficulties, but none of them have sought medical advice. The measured sound pressure level varied from 40 to 90 dBA, and 15% of the data was over 80 dBA. The results show the need for showing young people the importance of hearing protection and prevention of noise-induced hearing loss.Copyright

Effects of training, style, and rate of speaking on speech perception of young people in reverberation

Because of the difficulty of listening to speech in reverberation (e.g. train stations or airports), we need to find characteristics of intelligible speech sounds that are appropriate for announcements over loudspeakers in public spaces. This study investigated the effects of training (seven talkers who have received speech training or not), style (conversational/clear) and rate (normal/slow) of speaking on speech perception of young people in simulated reverberant environments. The talkers were instructed to speak nonsense words embedded within a carrier sentence clearly or normally in an anechoic room, and listening tests were carried out with young people in simulated reverberant environments. Results showed that correct rates significantly differed among the talkers, but no difference in correct rates was found between the two speaking rates, and conversational speech had significantly higher correct rates than clear speech. Casual inspections of the stimuli indicate that vowels are enhanced as well a...