Glottal Opening Measurements in VCV and VCCV Sequences
Benjamin Elie(1) , Angélique Amelot(2) , Yves Laprie(3) , Shinji Maeda(2)(1) Loria, France, benjamin.elie@loria.fr(2) LPP, France, angelique.amelot@gmail.com(3) Loria, France, yves.laprie@loria.fr

Abstract
Many studies on speech acoustics and production use articulatory synthesis as a framework to investigate therelationship between articulatory gestures and acoustic features. Although supraglottal articulatory models areavailable, usually built from vocal tract imaging acquisitions, glottal gestures are commonly modeled withsimple geometric primitives which do not necessarily reﬂect reality. This study is a ﬁrst step towards the development of a database of realistic glottal gestures which will be used to design the glottal opening dynamics inarticulatory synthesis paradigms. In the ﬁrst part of this paper, we present experimental measurements of glottal
opening dynamics in VCV and VCCV sequences uttered by real subjects, thanks to a speciﬁcally designed external photoglottographic device (ePGG). The corpus was designed to highlight the differences in glottis opening
between fricatives and stops. The existence of different patterns of glottal opening is evidenced according to theclass of the consonants. A numerical study is then used to show the inﬂuence of these patterns on the productionof sounds and on the coarticulation.
Keywords: Speech, Glottis, Consonants

1

INTRODUCTION

Glottis opening is one of the parameters which deﬁne the articulation mode. It is also an essential parameter for
exploring aerodynamic phenomena in the vocal tract with respect to the airﬂow. Recently, we have exploited theglottis opening data to explore the conditions of simultaneous existence of voicing and a frication noise for thevoiced fricatives [1]. In particular, we have shown that they correspond to a production regime that is difﬁcult
to maintain, which explains the relative rarity of voiced fricatives in languages, and the ﬁnal devoicing in somelanguages.
We therefore wanted to study glottis opening in a more systematic way, especially for the stops sounds. We
acquired these glottis opening data using electroglottography, a recently developed technology and, before using
this data in acoustic simulations, we ﬁrst wanted to develop the acquisition methodology, and conduct evaluationof those data for several speakers.
Glottis opening is difﬁcult to measure directly. The direct technique is ﬁbroscopy, which involves passing acamera through the nostril to image the vocal folds from the top of the pharynx. This is an invasive technique,and one additional difﬁculty is that the lack of light only allows a frequency of about 30 Hz to be reached.
Relative to the duration of a sound, i.e. between 50 and 100 ms for a vowel, this means that only 2 to 4 imagesof the vocal folds are obtained, and this is not enough to observe transitions between opening and closing of
the glottis ﬁnely.
Fast imaging offers a much better temporal resolution (between 2000 and 4000 images per second) but thecamera is ﬁxed at the extremity of a rigid tube and it is therefore possible to visualize the vocal folds forvowels only. Whatever the imaging technique, it is impossible to measure the area at the glottis and only
qualitative information is available.
Finally, transillumination technique [2] provides a far better sampling frequency because a photosensitive sensor
is placed on the neck below the glottis, but is still invasive because it requires a source light to be introduced
at the top of the pharynx through the nose.

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Figure 1. Position of the emitting diods and photosensitive sensor. The subject presses each of the two diodes
against her neck.
Electroglottography [3] is a non-invasive technique which provides a quantitative information about the contact
between vocal folds, as well as fundamental frequency as a by-product. The higher the contact between the
vocal folds, the stronger the conductance. Conversely, the conductance almost stabilizes at zero as soon as the
vocal folds are separated. This means that the temporal evolution of the glottis area is not precisely known assoon as there is no longer contact. This is an important weakness since this area has a direct impact about the
airﬂow in the vocal tract.
All these reasons motivated the development of the ElectroPhotoGlottoGraphy (EPGG) by Honda and Maeda [4],which provides information on the glottis opening area without being invasive. The principle consists in injecting light above the glottis and using a photosensitive sensor placed below the glottis to detect the light ﬂow
that depends directly on the surface of the opening. To avoid, or at least limit, the inﬂuence of visible light(natural or artiﬁcial) Honda and Maeda used infrared light. The system therefore consists of two infrared diodes
to emit light above the vocal folds and a photosensitive sensor placed below the glottis. A measuring unit anda microphone complete the device. As can be seen in the photo, the system is much smaller than the one
developed by Birkholz et al. [5].
1.1 First experiments and settings
The operating principle is quite simple, but it remains to verify the link between the amount of light recoveredby the sensor and the surface of the glottis area, and to deﬁne an effective experimental protocol.
For the ﬁrst point, Bouvet et al. [6] used a model of silicone vocal folds whose geometry is perfectly known.
A source of pressure is used to vibrate these artiﬁcial vocal folds. The EPGG system was ﬁxed on this model.
The measurements show that the recovered light ﬂow is an afﬁne function of the amount of light injected at
the entrance of the vocal folds. This validates this glottis opening measurement system.
For the second point we conducted a series of experiments on several speakers in order to know how EPGG
can be used, and to know the inﬂuence of the anatomical characteristics of the speakers. The ﬁrst observationis that the orientation of the light-emitting diodes has a very important impact on the measured light ﬂow. Theirorientation has thus to be adjusted with a good precision.
The second observation is that the vertical movement of the larynx has an important inﬂuence on the recovered
light ﬂow since the relative position of the diodes and the sensor with respect to the glottis opening changes.
The third observation is that the measurements depend strongly on the speaker, probably because of the varietyof tissues traversed by the light, and of course their thickness. We thus investigated a number of settings

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aSa

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Figure 2. EPGG signal (bottom) and acoustic signal (top) for /asa aSa afa/ and zoom on /aSa/
to optimize the quality of measurements. One of the difﬁculties is to ensure good contact between the lightemitting diodes and the neck. Initially we used an elastic strap band but to obtain a good contact it is necessarythat the strap is very tight which is not comfortable for the subject. Finally, we ask the subject to hold thediodes himself or herself (see Fig. 1) which has the additional advantage of partially blocking the movementsof the larynx, and therefore of obtaining a signal with a more stable baseline.
Figure 2 illustrates an EPGG acquisition for the 3 French unvoiced fricatives /s S f/. It can be noted that thevolume of light recovered is not zero when the glottis is closed, nor is the baseline constant. As also noted by
Sawashima and Hirose [7], it seems that there are still some vibrations after the glottis opens. But contrary totheir observations, there is still a residual voicing in the signal.
1.2 Corpus design
The ﬁrst experiments we carried out concerned the production of voiced and unvoiced fricatives [1] with respect
to the glottis opening strategies. The measurements made on this occasion showed that the glottis opening isstronger for unvoiced fricatives than for all other sounds, except for breathing. Since the amount of lightdepends on the position of the larynx, we looked for a way to normalize the measurements. Glottal opening
for /asa/ presents the double advantage of being sufﬁciently large without being the greatest opening, and stableenough. During the construction of the corpus we therefore introduced /asa/ as a normalization sequence before
and after each item. Each utterance is thus of the following form: /asa/ item /asa/ The corpus is therefore madeup of the following items:• VCV where V is a cardinal vowel and C belongs to {p t k b d g f s S v z Z l m n K},• aC1C2 a where V is a cardinal vowel, C1 belongs to {b d g} and C2 to {l K},• asCa where C belongs to {b d g p t k},• geminated stops in /pap papa/ ("pape papa"), /pat tatue/ ("patte tatouée"), /sak kaKe/ ("sac carré"), /kKabbagaKœK/ ("crabe bagarreur"), /pad dat/ ("pas de date"), /blag gaKãti/ ("blague garantie"),• 4 sentences of variable length.
This small corpus covers all the consonants, some of the most frequent clusters in French, especially those with
/K/, geminated stops and some sentences. The corpus has been recorded by 3 female and male French speakers.

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Figure 3. EPGG signal for /asa papa sa/, /asa kaka sa/ and /asa titi sa/

2

Analysis of glottis opening for stops

Figure 3 shows that the glottis opening is considerably smaller for unvoiced stops than unvoiced fricatives. The
complete data conﬁrms this trend. The ﬁrst explanation is that the production of fricatives requires maintaining aturbulent ﬂow throughout the duration of the fricative, and consequently a large opening to ensure a sufﬁcient air
ﬂow. On the contrary, the production of unvoiced stops only requires stopping the vibration of the vocal folds
and ﬁlling the cavity behind the constriction in order to achieve an overpressure with respect to atmosphericpressure.
The peak of the opening is reached approximately in the middle of the segment formed by the closure andburst, i.e. the moment during which there is no more voicing. On the 3 examples /papa kaka titi/ it can benoted that the opening is larger for /kaka/ than /papa/, and that it is bigger for /titi/ than /kaka/. This increaseof the opening coincides with the existence of an increasingly intense frication noise following the release burst.
Overall, the same trend can be observed for /u/ and /i/ compared to /a/, i.e. a larger opening during the closure.
From the point of view of the larger glottis opening for the vowels /i/ and /u/, the tongue has to anticipate
the position it will have after the occlusion is released. The cavity volume behind the constriction is therefore
larger, and a larger opening is required to bring a sufﬁcient amount of air. Compared to /t/ and /k/, /p/ does not
impose any constraint on the tongue, which can therefore fully anticipate its position for the following vowel.
Since the vowel /i/, and to a lesser extent /u/, are characterized by a back cavity of a larger volume than /a/
it is therefore necessary to maintain a larger opening to allow enough air to enter. The volume of air behindthe constriction, and the vocal tract shape also explains the duration of the global burst, i.e. from the transientnoise corresponding to the release of the constriction to the ﬁrst voiced period.
Overall, the larger the cavity behind the constriction and the smaller the area in front of the vocal tract for the
next vowel, i. e. /i/ and /u/, the longer the burst duration for the overpressure to vanish. On the other hand, theback cavity of /a/ is very narrow and therefore not very voluminous, which leads to a minimal burst duration,
especially for /p/ since the tongue can anticipate its back position very early.
Although the larynx moves over time, Figure 2 shows that the glottis opening is absent or very small for thevoiced stops. However, there is a small opening in the case of /didi/ which gives rise to a slight frication noisein high frequency. The rest of the data conﬁrms this trend.

3

Analysis of glottis opening for stops

We also acquired data for consonant clusters, especially when the second consonant is /K/. In the case of an
unvoiced stop the presence of /K/ results in a glottis opening that is much larger than that of the unvoiced stop
alone in order to produce a frication noise after the burst. The opening is almost zero when /K/ follows a voicedstop (see Figure 5). The difference between /kKa/ and /gKa/ is therefore very strong since there is no glottis
opening for /gKa/. It turns out that the voicing mode is entirely determined by the consonant preceding /K/.

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Figure 4. EPGG signal for /asabasa/, /asagasa/ and /asa didi sa/

Figure 5. EPGG signal for /asa kKa sa/ and /asa gKa sa/
Despite this absence of opening, the vocal folds stop vibrating during /K/ in the case of /gKa/ but not in theother voiced cases /bKa/ and /dKa/, either because the constriction is almost complete at the constriction level/gKa/, or because the volume of the cavity before the constriction is sufﬁcient for /bKa/ and /dKa/ to maintain apressure difference that allows the vibration of the vocal folds.

4

CONCLUDING REMARKS

Apart from the consonants that motivated this work, these EPGG data illustrate the speaker strategy at the levelof a sentence. The speaker begins with a breath that results in a long glottis opening. He/she then closes itcompletely just before starting a voiced sound (about 100 ms) in order to reach a sufﬁcient subglottal pressure.
There is also an almost complete closure when the sentence begins with an unvoiced fricative but the closing
gesture does not completely ﬁnish until a new opening gesture corresponding to the fricative starts. We usedthose data to design the algorithm that sets the opening to the glottis for our copy synthesis experiments [8].

ACKNOWLEDGEMENTS
This work is supported by the ANR grant “ArtSpeech” (2015-2019).

REFERENCES
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