Effects of length of carrier phrase on release from masking
in multi-talker voice guidance
Hayato SATO1∗ , Masayuki MORIMOTO1 , Kazuhiro IIDA2 , Hiroshi SATO3
1 Kobe University, Japan
2 Chiba Institute of Technology, Japan
3 National Institute of Advanced Industrial Science and Technology, Japan

Abstract
Multilingualization of voice guidance is necessary for international passenger facilities and world famous
tourist sites. When the voice guidance is provided by public address systems, normally the same content issequentially broadcasted in several languages. The authors are advancing a challenging project to shorten therequired time by simultaneously broadcasting all of the guidances. In this paper, as a basic study, a listening
test on word intelligibility of multi-talker voice guidance was performed to clarify effects of length of carrierphrase. The target stimulus consisted of two different Japanese words by two different talkers which were
simultaneously reproduced. The task of the listener was to answer both of the two words. As a carrier phrase,other Japanese words spoken by the two talkers were sequentially reproduced prior to the target stimulus. The
carrier phrase and the target stimulus were presented from a loudspeaker installed in front of the listener. The
parameters of the test were length of the carrier phrase and combination of pitches of the two talkers’ voices.
As a result, the length of the carrier phrase tended to affect the word intelligibility scores. However, the slope ofthe score with respect to the length widely varied from positive to negative depending on the test parameters.
Keywords: Multilingualization, Voice guidance, Cocktail party effect1

INTRODUCTION

In places full of international visitors, such as transport hubs, cosmopolitan cities, and world famous tourist
sites, multilingual voice guidance is provided. When the voice guidance is provided by public address systems,
normally the same content is sequentially broadcasted in several languages. However, the required time to finish
the guidance for all languages is very long and the user have to wait a turn of his/her mother language.
Based on the idea that release from masking by the cocktail party effect (1) can be a solution for this problem, the authors are advancing a challenging project to shorten the required time by simultaneously broadcasting
all of the guidances.
The cocktail party effect is often treated as one of the advantages of binaural listening. It is known thatspatial release from masking increases the intelligibility of target speech when the target speech and the masker
come from different directions. For examples, Duquesnoy (2) reported that when both the target and the masker
were speech, a Speech Recognition Threshold (SRT) improvement of about 6 dB was observed by changing thedirections of the target and the masker. Hawley et al. (3) conducted experiments using multi-talker maskers andalso reported that there was an improvement in SRT of 6 to 7 dB by spatial release from masking.
On factors other than spatial release from masking that affect the segregation of multi-talker speech, there areseveral researches that investigated the effects of similarity between the target and the maskers. With regard to
the difference in the fundamental frequency or pitch, Festen and Plomp (4) and Brungart et al. (5) reported thatthe intelligibility of the target speech was clearly improved when the gender of the target talker was different
from that of the masker talker. On the linguistic difference between the target and the maskers that should∗ hayato@kobe-u.ac.jp5862

be taken into consideration in our project, van Engen and Bradlow (6) and Calandruccio et al. (7) reported
that the intelligibility of the target speech increased when the language of the target was different from thatof the masker, in severe listening conditions (for example, when the sound pressure level of the masker waslarger than that of the target). It should be noted that, as Mattys et al. (8) and Brouwer et al. (9) pointed out,
which of acoustic similarity or linguistic similarity dominantly affect the intelligibility depends on the listener’s
proficiency on the target or the masker language.
Furthermore, it is known that the uncertainty or familiarity of the target and the masker also affects theintelligibility in multi-talker situations. Brungart and Simpson (10) compared the intelligibility when the talker
or the content of masker speech were fixed and when they were random, and reported that the intelligibility
scores for the fixed conditions were higher than those for the random conditions especially when the content
was fixed. Nygaard and Pisoni (11) reported that the word intelligibility score was increased by training sessions
to familiarize the utterance of the talker of the target word, and the training using sentences was more effective
than that using words. Jonsrude et al. (12) reported that the intelligibility was higher when either the target or
the masker was the spouse’s voice than when both the target and the masker were unfamiliar voices, although
the improvement was smaller when the spouse’s voice was the masker than when it was the target.
As described above, many factors need to be considered in order to optimize multilingual simultaneous voice
guidance. Considering the above-mentioned past studies, a multi-loudspeaker system will be the most effective
to multilingual simultaneous voice guidance, because it can utilize spatial release of masking which is assumed
to have the largest effect on the intelligibility in multi-talker situations. However, considering that the guidanceis provided to a number of unspecified listeners scattered in the space, it is desirable to be able to keep a highintelligibility as much as possible even when the guidance is provided from a single loudspeaker because thedegree of spatial release of masking depends on the position and orientation of the listener. Therefore, in thepresent study, a simple system using a single loudspeaker was investigated as a basic study.
The purpose of the present study is to investigate methods to improve the intelligibility of multilingual
simultaneous voice guidance using a single loudspeaker system. Specifically, a method of providing the target
talker’s speech as the carrier phrase just before the target speech was investigated. The past studies (11) (12)showed that relatively long-term learning of target speech features increased the intelligibility, however, it isunclear whether the increase can be obtained by listening the target taker’s speech just before the target. The
length of the carrier phrase and the gender of the talker, which were expected from the past studies to affectthe intelligibility, were used as the parameters of the listening test.
In the case of using multi-language speech materials as test stimuli, it is necessary to design complicatedexperimental conditions in order to investigate the effect of the listener’s proficiency on the target/masker language and the effect of the combination among languages. Here, to simplify the purpose of the study, only
the condition considered the most severe that both the target and the masker language are the listener’s motherlanguage was tested. In this case, since the listener can not distinguish which speech stimulus is the target or
the masker, the listener was asked to answer both of them.

2

METHOD

2.1 Test words
240 Japanese words were used as test words. Test words were selected from the FW03 word list (13) to be
most familiar to young adults. Each test word has 4 syllables. Test words were spoken by two female talkers(fhi and fto) and a male talker (mya), and recorded in an anechoic room. The fundamental frequencies averaged
over 10 sampled words were 262 Hz, 253 Hz, and 145 Hz for the talkers of fhi, fto, and mya, respectively.
2.2 Stimuli and test conditions
Each stimulus was consisted of a carrier phrase (or sound) and two target words as shown in Fig. 1. The
carrier phrase was consisted of several words sequentially spoken by two different talkers. The target stimulus

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Figure 1. Example of temporal pattern of stimulus (carrier phrase: 2 talkers × 2 words).
was two different words simultaneously spoken by the two different talkers who were the same as those forthe carrier phrase. In order to analyze effects of pre-listening the voices of talkers for the target stimulus, asteady-state speech-like noise was used as a carrier sound. The spectrum of noise was determined using Eq. 1.
SN ( f ) =S f hi ( f ) S f to ( f ) Smya ( f )
+
+
,
4
4
2

(1)

where, SN ( f ), S f hi ( f ), S f to ( f ), and Smya ( f ) are long-time average spectra for the carrier noise, the test words
spoken by fhi, fto, and mya for the frequency of f, respectively. The length of the noise was set to the average
length of 4 test words (3.3 s). The interval between the carrier phrase (sound) and the target stimulus was 1 s.
The equivalent continuous A-weighted sound pressure level for each word and that for the noise were set to be
65 dB.
Table1 shows test conditions used in the present study. Test parameters were the length of carrier sound(2, 4, and 6 words), the type of carrier sound (speech and noise), and the combination of talkers (fhi–fto andfhi–mya).
Table 1. Test conditions
Condition
1
2
3
4
5
6
7
8

Carrier 1
Carrier 2
fhi: 1 word
fto: 1 word
fhi: 2 words
fto: 2 words
fhi: 3 words
fto: 3 words
noise (4 words length)fhi: 1 word
mya: 1 word
fhi: 2 words mya: 2 words
fhi: 3 words mya: 3 words
noise (4 words length)

Targetfhi + fto
fhi + fto
fhi + fto
fhi + fto
fhi + mya
fhi + mya
fhi + mya
fhi + mya

2.3 Participants
16 young adults participated in the listening test. They were university students in their twenties. The resultsof pure-tone audiometry show that all participants had normal hearing sensitivity.
2.4 Procedures
160 test words were used as the target words, and the rest 80 test words were used to construct the carrierphrase. Each participant listened to 10 stimuli per condition, in other words, a total of 80 stimuli. Each target
test word was presented to the same participant only once, while the words for the carrier phrase were presented
twice. The combinations of the test conditions and the target words were different for each participant. All of5864

the target words were presented once for each condition after 16 participants finished the listening test. The
listening test was divided into 5 sessions to listen to 16 stimuli. The stimuli were presented in random order.
The stimulus was presented from a loudspeaker (Eclipse, TD508II) at a distance of 1.5 m in front of theparticipant in an anechoic room. Each participant was asked to take dictation of both of the target words as theylistened using katakana characters (Japanese phonograms). Before the listening test, each participant listened to
8 stimuli which consisted of words other than the 240 test words as an exercise.

3

RESULTS AND DISCUSSION

Word intelligibility scores for each conditions were obtained from the collective results of the listening test
for all participants. This means that the number of samples for each condition was 160. The word intelligibility
score is the percentage of the target words written down correctly.
3.1 Similar pitch conditions
Figure 2 shows the results for the conditions 1–4, where the target words were spoken by fhi and fto, in
other words, the two target words had a similar pitch. The x-axis of Fig. 2 represents the carrier phrase/soundfor each condition. For example, the label “4 words” corresponds to the condition 2 where the carrier phrase
consists of 2 words by fhi and 2 words by fto. Table 2 shows p-values obtained by Chi-squared tests between
the scores.
The scores of fto were higher than those of fhi in all conditions. The p-values of Chi-squared test between
the scores of fhi and fto for the conditions 3 and 4 were 0.058 and 0.089 respectively, and they were almost
statistically significant. Considering that there was a difference in the scores even under the condition 4 where
the noise was presented instead of the carrier phrase, the interference between the voices of fhi and fto seemed
to be asymmetry regardless of whether or not the listeners had listened to the voices in advance. In order toclarify the cause of this difference, a detailed analysis of speech stimuli is required, but it is beyond the scopeof the present study and not be done here.
The score tended to increase as the length of the carrier phrase increased. In the case of fhi, the increase
was only 3 percent points, and the p-values did not show statistical significance. In the case of fto, the increase
was slightly large at 8 percent points, and the p-value between the conditions 1 and 3 (between the carrierphrase of 2 words and that of 6 words) was 0.08. The effect size (Cohen’s h) for the comparison between
the conditions 1 and 3 was 0.198, and this means that one can expect that the length of the carrier phrase
causes a small difference of the scores. However, the difference can not be detected as a statistically significant
difference because of the small number of samples in the present study. The difference in the effect of thecarrier phrase length between fhi and fto can be explained by the temporal position of fto’s voice in the carrierphrase: While the fto carrier phrase was always adjacent to the target words, the fhi carrier phrase was more
widely separated from the target words under longer carrier phrase conditions. It is likely that the listeners
could pay attention to the voice of fto quickly by using the fresh image of the voice in their working memory,and this caused relatively large amount of informational masking release.
It should be noted that the scores of fto in the condition 4 was higher than that in the condition 1, although
the p-value between them was 0.231. This implies that information included in the carrier phrase may degrade
the scores in some cases.
3.2 Different pitch conditions
Figure 3 shows the results for the conditions 5–8, where the target words were spoken by fhi and mya, inother words, the two target words had a difference in pitch. Table 3 shows p-values obtained by Chi-squared
tests between the scores.
The differences between scores of fhi and mya were not significant in all conditions. The scores ranged from
81% to 88%, and they were higher than the similar pitch conditions shown in Fig. 2. Table 4 shows p-values

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Figure 2. Word intelligibility scores for each target stimulus in the conditions 1–4.
Table 2. The results (p-value) of Chi-squared tests for conditions 1–4.
(a) Between talkers
Condition
1
2
3
4
0.453 0.157 0.058 0.089

Talkerfhifto(b) Between conditions
Pair of conditions
1–2
1–3
1–4
2–3
2–4
0.902 0.533 0.805 0.617 0.901
0.431 0.077 0.231 0.325 0.680

3-4
0.706
0.567

obtained by Chi-squared tests between the scores of fhi for each carrier phrase/sound. Except the case that thecarrier phrase was 6 words, the scores of fhi in the different pitch conditions were significantly higher thanthose in the similar pitch conditions (p<0.05). This result can be explained by informational masking release
due to the difference in pitch between competing voices.
The score tended to decrease as the length of the career phrase increased, although the p-values did notshow statistical significance. This tendency was rather apparent for fhi, and the p-value between the conditions
5 and 7 was 0.124. It is curious that this tendency was opposite to the similar pitch conditions. As mentioned
in the previous section, this result implies that the carrier phrase used in this study had the useful effect while
it also had the detrimental effect on the scores. A possible explanation for these results is as follows. The
carrier phrase was a sequence of irrelevant words and its content changed with each presentation. Although
the listeners were not asked to memorize the carrier phrase, this feature might have increased the listener’s
working memory load and consequently decreased the scores. In the different pitch conditions, the listeners
could easily segregate the two target words so that the useful effect of the carrier phrase was disappeared while
the detrimental effect remained.
Table 3. The results (p-value) of Chi-squared tests for conditions 5–8.
(a) Between talkers
Condition
56
7
80.741 0.652 0.459 0.636

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Talkerfhimya(b) Between conditions
Pair of conditions
5–6
5–7
5–8
6–7
6–8
0.210 0.124 0.741 0.772 0.356
0.636 0.636 0.636 1.000 1.000

7–8
0.225
1.000

Figure 3. Word intelligibility scores for each target stimulus in the conditions 5–8.
Table 4. The results (p-value) of Chi-squared tests between the scores of fhi in the similar pitch conditions andthose in the different pitch conditions for each carrier phrase/sound.
2 words<0.001

Carrier phrase/sound4 words 6 words
0.017
0.108

Noise
0.002

3.3 Toward applying the carrier phrase to multi-talker broadcast
The results obtained in the present study suggested that the carrier phrase may have both useful and detrimental effects on the intelligibility of the target multi-talker speech. The longer the carrier phrase, the stronger
the useful effect, meanwhile, however, the interval from the carrier phrase to the target speech also affected.
Therefore, there is room for optimization as to how to arrange each talker’s voice in the time axis. With regard
to the detrimental effect, it is necessary not to increase the working memory load of the listener as much as
possible. For example, using the fixed carrier phrase without critical information every time to decrease uncertainty may be a reasonable solution. Although the increase in intelligibility by the carrier phrase in the present
study was small, if it was the result that the useful and detrimental effects were offset, it can be expected thatthe intelligibility will further increase by optimization.

4

CONCLUSIONSAs a basic study toward realizing multilingual simultaneous voice guidance, the effect of carrier phrase
on multi-talker speech was investigated using a word intelligibility test. The target stimulus consisted of two
different Japanese words by two different talkers which were simultaneously reproduced. The task of the listener
was to answer both of the two words. The carrier phrase consisted of the two talkers’ voices. The parameters of
the test were length of the carrier phrase and combination of pitch of the talker’s voice. The results suggested
the following conclusions.
(1) The length of the carrier phrase tended to affect the word intelligibility scores. However, the slope of thescore with respect to the length varied from positive to negative depending on the test parameters.
(2) From (1), information contained in the carrier phrase may have both useful and detrimental effects onword intelligibility scores. In order to optimize the carrier phrase so that only useful effects can beobtained, further studies are required focusing on each parameter of the carrier phrase such as length,
difference in pitch between talkers’ voices, order of each talker’s voice, uncertainty of contents.

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ACKNOWLEDGEMENTS
The authors express their gratitude to the listeners. This work was partially supported by JSPS KAKENHI
Grant Number 18H01597. The authors would like to thank Sakino Kataoka for her practical support in thiswork.

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