PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Reverberation-induced speech improves intelligibility inreverberation: Effects of taker gender and speaking rate
Nao Hodoshima11Tokai University, JapanABSTRACT
Humans adjust their speech when speaking in noise to enhance their intelligibility (known as the Lombard
effect). Speech spoken through noise (noise-induced speech) is generally more intelligible than that spoken
in quiet when heard in noise. The author has reported that “reverberation-induced speech” also improves
speech intelligibility in reverberation, although the masking of noise and reverberation differed. The present
study investigates whether reverberation-induced speech intelligibility depends on the gender and speaking
rate of talkers. Four talkers (two males and two females) spoke under quiet (Q) and reverberation (R)conditions. In R, the reverberant speech was fed back to the talkers via headphones. Then speaking rate wasadjusted to 1.2 (fast), 1.0 (original), and 0.8 (slow). 18 participants performed word identification tests inreverberation (reverberation time of 3.6 s). The results showed that speech was significantly more intelligible
under R than Q, male talkers were significantly more intelligible than females, and slow speech wassignificantly more intelligible than fast speech. And the improvement in speech intelligibility under R
compared with Q was not significantly affected by the speaking rate. These results suggest that reverberationinduced speech regardless of the speaking rate might increase intelligibility of announcements in public
spaces such as airports.
Keywords: Reverberation, Speech production, Lombard effect, Speech intelligibility, Speaking rate

1. INTRODUCTION
Noise and reverberation generally degrade speech intelligibility compared with quiet environments.
In addition, speech intelligibility in noisy or reverberant environments is generally lower for olderadults and people with hearing impairments when compared with young adults without hearing loss
[1]. The population of older adults is rapidly increasing. For example, as of 2018, people older than
65 years comprised 27.7% of the total population in Japan [2]. Therefore, care must be taken whenbroadcasting announcements in public spaces (e.g., train stations and airports), especially inemergency situations.
During speech communication, humans have a natural tendency to modify their speech in order tomake it more robust against noise. This is widely known as the Lombard effect [3]. When comparedwith speech spoken in quiet environments, intensity, duration, fundamental frequency, and firstformant frequency are increased in speech spoken in noisy environments [4, 5]. In addition, speech
spoken in noisy environments has higher word intelligibility than that spoken in quiet environments,
as judged by young adults in noisy environments [3–5].
In reverberant environments, similar results have been observed, although with noise andreverberation masking patterns that are temporally and spectrally different (noise masks speech
simultaneously, while overlap-masking occurs in reverberation [6]). When compared with speech
spoken in quiet environments, the intensity, fundamental frequency, and first formant frequency havebeen found to be increased in speech spoken in reverberation [7]. When participants listen to speech
spoken in reverberant environments, it has been reported to be more intelligible for young and older
adults compared with speech spoken in a quiet environment [8, 9].
Speaking slowly generally increases speech intelligibility, especially for older adults, because
cognitive aging might result from a general slowing of processing speed [10]. Time-compressedspeech (with a time compression rate of 40%) results in lower intelligibility for older than for younger
adults in noisy or reverberant environments [11]. Significant interaction has been observed between
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hodoshima@tokai-u.jp

speech expansion and pause expansion, and higher speech intelligibility has been obtained with ashort time expansion (100 ms) compared with non-expanded speech when the pause between phrases
was 300 and 400 ms for both young and older adults in a noisy environment [12]. Slowing the speaking
rate (with an expansion rate of 120%) has been shown to improve speech intelligibility in a reverberant
environment [13]. However, to our knowledge, no studies have investigated whether the speaking rateaffects the intelligibility of speech spoken in a reverberant environment.
Speech intelligibility differs by gender depending on several different experimental conditions. In
a previous study, female talkers (5 talkers) had higher correct word rate than male talkers (5 talkers)
in a noisy environment, regardless of listener gender [14]. In addition, vowel intelligibility in a noisy
environment varied widely among 41 talkers for normal and clear speech (clearly articulated speech),and female talkers showed a larger clear speech vowel intelligibility benefit than male talkers [15]. A
male talker enunciating in either a normal or an urgent style resulted in a higher correct and faster
identification rate in a noisy environment than a female talker [16]. Therefore, talker gender may
affect the intelligibility of speech spoken in a reverberant environment.
The aim of the present study was to investigate whether the speech intelligibility of speech spoken
in reverberation depends on the talker and speaking rate, with the goal of making spoken
announcements in public spaces more intelligible. We would like to accomplish this by modifying theinput of broadcasting announcements from loudspeakers (e.g., broadcasting speech spoken in noiseor reverberation), such that architectural acoustical and/or electroacoustical treatments are notrequired in public spaces.

2. EXPERIMENT
2.1 Participants
The participants were 18 native speakers of Japanese aged 21–24 years with self-reported normalhearing.
2.2 Stimuli
Four native speakers of Japanese (two males [M1, M2] and two females [F1, F2], aged 21–22years) who self-reported no hearing or voice disorders served as talkers.
The speech materials consisted of 50 target words embedded in a carrier sentence. The target words
were four morae (a phonological syllable-like unit in Japanese) that were selected from a database offamiliarity-controlled Japanese word lists (FW03) [17]. Word familiarity in this study was chosen
between 2.5 and 4.0 on a 7-point scale (1 for the least familiar and 7 for the most familiar).
The speech materials were recorded on a computer through a microphone (SHURE KSM141;condenser, cardioid) and a digital audio interface (TASCAM US-144MKII) in a sound-treated room(see Figure 1) at a sampling frequency of 44,100 Hz. Two speaking conditions were used in therecording: quiet and reverberation. Under the reverberation condition, talker utterances wereconvolved by an impulse response recorded in a church, and reverberant sounds were fed to the talkers
through headphones (SENNHEISER HDA200; dynamic, closed circumaural type). The playback level
was set to –10 dB relative to the speaking level at the talker’s ears. The reverberation time was 3.6 sfor octave bands from 125 to 4000 Hz. The recording was controlled by Adobe Audition 3.0 (the delaytime caused by the software was less than a few ms). The talkers were asked to imagine that theirspeech was being broadcast into a public space with the same room acoustics they were experiencing
through the headphones, and instructed to speak as clearly as possible.
After the recording was finished, one carrier sentence was chosen, and the target words with fixed
preceding and following pauses were embedded in the carrier sentence for each speaking conditionand each talker. This was done to control the effect of overlap-masking on the target words. Next, theintensity ratio of the carrier sentence relative to the target word was normalized across each speaking
condition and speaker.
Then, the speaking rate was changed to slow (70% of the original speaking rate) and fast (120%of the original speaking rate) using the Praat software, which applies a pitch-synchronous-overlapadd (PSOLA) method for time-scale modification. The PSOLA method can modify the speaking rate
without changing the fundamental or formant frequencies of the original speech [18].
Finally, the concatenated speech sounds were convolved with the impulse response, which was thesame as that used in the recording. The overall intensity of the stimuli was normalized across speaking
conditions and talkers. The total number of stimuli was 1200 (two speaking conditions  three6191

speaking rates  four talkers  50 sentences). Table 1 shows the experimental conditions used in thelistening test.
2.3 Procedures
The listening test was carried out in a sound-treated room. Stimuli were presented to eachparticipant diotically over headphones (SENNHEISER HDA 200) through a digital audio interface(TASCAM US-144MKII) connected to a computer. Two practice trials were held to familiarize theparticipants with the experimental procedure.
The playback level was adjusted to each participant’s comfort level. In each trial, a stimulus waspresented once, and the participants were instructed to write down what they heard as a target wordon their answer sheets. For each participant, 48 stimuli (two speaking conditions  three speaking
rates  two talkers  four sentences) were presented randomly. The target word and listening condition
combinations were counter-balanced across the participants.

Figure 1 – Recording setup
Table 1 – Experimental conditions
Speaking rateSpeaking condition
Quiet

Reverberation

OriginalQR

FastQF

RFSlowQS

RS

3. RESULTS AND DISCUSSION
Figure 2 shows the mean percent correct mora rates of the target words for each condition andtalker. Statistical analyses were carried out using IBM SPSS Statistics. A mixed analysis of variance
was carried out with the speaking condition (Q and R) and speaking rate (original, fast and slow) as
repeated variables, the talkers as the between-subjects variable, and the correct mora rate as thedependent variable.
The main effect of the speaking condition was significant (p < 0.01). This result indicates thatreverberation-induced speech was more intelligible than speech spoken in a quiet environment when
the listeners listened in a reverberant environment, which is consistent with the results of previous
studies [8, 9].
As expected, the main effect of the speaking rate was significant (p < 0.01), and a post hoc test
revealed that the normal speaking rate had higher speech intelligibility than the fast speaking rate (p= 0.003), the slow speaking rate had higher speech intelligibility than the normal speaking rate (p =0.016), and the slow speaking rate had higher speech intelligibility than the fast speaking rate (p <0.01). These results are consistent with those of a previous study [13] (both of these studies carriedout listening tests in a reverberant environment).
The talker effect was significant (p < 0.01), and a post hoc test revealed that F1 had a significantly
lower correct rate than the other talkers (p < 0.01). These results suggested that the reverberantinduced speech was clearly dependent on the talkers. This talker-dependent intelligibility is consistent
with normal speech [14], clear speech [15], and urgent speech [16], whereas the listening environment6192

was different (all previous studies [14–16] were conducted in a noisy environment, whereas thepresent study was carried out in a reverberant environment). When merging the results of the fourtalkers into gender, male talkers were more intelligible than female talkers (p < 0.01). However, thecorrect rates for the quiet condition for F1 appeared to be considerably lower than the other conditions
and talkers. Therefore, it remains unclear whether the speech intelligibility of reverberation-induced
speech depends on gender; future research should investigate this question further.
The interaction between the speaking condition and the speaking rate was not significant (p =0.066). This result suggests that reverberation-induced speech increased speech intelligibility in areverberant environment, regardless of the speaking rate.

Figure 2 – Mean correct mora rate and standard error of target words for each condition and talker

4. CONCLUSIONSThe present study carried out a listening test to investigate whether the intelligibility ofreverberation-induced speech differed in terms of the speaking rate and talkers. The results of listening
tests in a reverberant environment obtained from 18 participants showed that reverberant-induced
speech was significantly more intelligible than that spoken in a quiet environment. The results also
showed that slow speech was significantly more intelligible than normal and fast speech. These results
were consistent with those from previous studies. The results also showed that male talkers weresignificantly more intelligible than female talkers; however, the results also suggest that speech
intelligibility is more talker-dependent. The improvement in speech intelligibility under thereverberation-induced speech condition compared with the quiet condition was not significantlyaffected by the speaking rate.
Since this was a preliminary study to determine the effects of reverberant-induced speech indifferent speaking rates and talkers, further research is needed with more talkers and a wider range ofreverberant conditions. In addition, acoustical analyses of reverberant-induced speech should becarried out.
The results of the present study revealed that reverberation-induced speech might increase theintelligibility of announcements in public spaces such as airports, regardless of the speaking rate.
Further research is needed to determine the appropriate combinations of the speaking rate and talker
characteristics to improve further the intelligibility of emergency public-address announcements.

ACKNOWLEDGEMENTS
This work was supported by a Grant-in-Aid for Scientific Research (C) from the Japan Society for
the Promotion of Science (18991829). We are grateful to Hideki Tachibana, Kanako Ueno, and Sakae6193

Yokoyama for providing the impulse response data, and to Hikaru Kawakami for carrying out thelistening test.

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