What Is a Speech Chain and How Can This Concept Be Applied to

the Various Areas of Speech Communication in an Intelligent

Society?

Takayuki Arai

Dept. of Information & Communication Sciences, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo, Japan

Keywords: Speech Chain, Speech Communication, Speech Production, Speech Perception, Vocal-tract Models, My

Voice Project.

Abstract: The concept of “Speech Chain” introduced by Denes and Pinson is widely used to interpret speech

communication systems. The concept was originally aimed at human speech communication: a speaker first

forms a message in his/her brain, the message is transformed into an acoustic signal that is sent to a listener,

and the listener decodes the signal back into the original message. This simple situation can be extended to

many scenarios. The acoustic signal can be fed into a telephone and transmitted over a telephone network. In

human-computer communication, the speaker can be a speech synthesis system or the listener can be an

automatic speech recognition system. For people who have lost the ability to talk, a speech synthesis system

can improve their quality of life, and for people who have impaired hearing, an automatic speech recognition

system can be a saviour. Communication with others is crucial as we live with other people in a society. As

societies transform into intelligent societies, it is even more important to investigate speech communication

systems from a scientific point of view and develop relevant applications in accordance with scientific

findings. In this talk, the speech production mechanism will first be reviewed by using a set of vocal-tract

models. Then, Speech Chain variations will be introduced for various areas in speech communication. Finally,

application of the Speech Chain concept to an intelligent society through our “My Voice” project will be

shared.

1 INTRODUCTION

The “Speech Chain” concept was originally

introduced by Denes and Pinson (1993), whose book

features a drawing of two people communicating with

each other via acoustic signals (i.e., speech sounds).

Such a human speech communication system

contains several levels. First, a speaker forms a

message in his/her brain, and words are selected and

ordered to express the message. This is called the

“linguistic level” because the speaker uses linguistic

knowledge such as vocabulary and grammar. Based

on the word sequence composed at the linguistic

level, vocal and speech organs are moved to phonate

and articulate speech sounds via the nervous system

and muscles. This is called the “physiological level.”

Then, speech sounds are produced and propagated

from the speaker and reach the listener. This is called

https://orcid.org/0000-0003-1084-8083

the “acoustic level.” In the peripheral auditory

process, the sounds are converted from mechanical

vibrations into nerve signals on the physiological

level. The nerve signals are transmitted to the

listener’s brain, and the original message is

constructed or decoded by applying linguistic

knowledge on the linguistic level. The speaker’s ears

also receive the speaker’s own speech sounds. In

other words, the speaker is always monitoring their

own output sounds. Thus, all events are chained;

therefore, they are collectively a speech chain.

Communication with others is crucial as we live

with other people in a society. As societies transform

into intelligent societies, it is even more important to

investigate speech communication systems from a

scientific point of view and develop relevant

applications in accordance with scientific findings.

Therefore, first, we will review the speech production

mechanism using a set of vocal-tract models. Next,

Arai, T.

What Is a Speech Chain and How Can This Concept Be Applied to the Various Areas of Speech Communication in an Intelligent Society?.

DOI: 10.5220/0010743600003113

In Proceedings of the 1st International Conference on Emerging Issues in Technology, Engineering and Science (ICE-TES 2021), pages 5-8

ISBN: 978-989-758-601-9

we will introduce speech chain variations for various

areas of speech communication. Finally, we will

share an example of utilizing the speech chain

concept in an intelligent society through our “My

Voice” project.

2 VOCAL-TRACT MODELS

In this section, we review human speech production

by introducing physical models that imitate various

phenomena that occur as we produce speech sounds

(Arai, 2007, 2012, 2016).

2.1 Lung Models

As the speech chain concept, a message is formed in

a speaker’s brain, and a word sequence is composed

based on the speaker’s linguistic knowledge. Speech

sounds are produced for the word sequence, and

speech production is usually done during exhalation,

which is part of the base human activity of breathing

with lungs.

The bottom part of Fig. 1 shows a lung model with

balloons (Arai, 2007). The phase of inhalation is

when the pink diaphragm changes the volume of the

thoracic cavity, and the air pressure inside the cavity

becomes negative when the diaphragm is pulled down

because the volume of the sealed cavity increases.

During this phase, the two balloons sitting inside the

cavity are inflated to compensate for the gap between

the air pressures inside and outside the cavity.

However, during the phase of exhalation when the

diaphragm is pushed up, the volume of the cavity

decreases, the air pressure inside the cavity becomes

positive, and the air inside the balloon goes out

through the larynx.

2.2 Artificial Larynx

In Fig. 1, the blue arrow indicates the location of an

artificial larynx (Arai, 2007). During exhalation, the

air goes through the artificial larynx and produces a

glottal sound by vibrating the membrane of the larynx

(i.e., “phonation”). Figure 2 shows a reed-type

artificial larynx (Arai, 2012). In Fig. 2, the air coming

from the pump goes through the reed-type larynx and

causes the reed to vibrate. That also makes a similar

glottal sound.

2.3 Vocal-Tract Models

The top part of Fig. 1 shows a head-shaped model

(Arai, 2007) that produces vowel /a/ because its

cavity forms a vocal tract when we produce vowel /a/.

The gray part in Fig. 2 is a straight tube imitating a

vocal-tract area function along the length of the

human vocal tract (Arai, 2012). Because the area

function in this case is based on the vowel /o/, the

output sound through the vocal-tract model in Fig. 2

sounds like /o/.

Figure 1: The lung model, an artificial larynx (blue arrow)

and a head-shaped model.

Figure 2: The air pump (in blue), a reed-type sound source

(left) and a vocal-tract model (right).

ICE-TES 2021 - International Conference on Emerging Issues in Technology, Engineering, and Science

Figure 3: The vocal-tract models, VTM-T20. Vowels /i/,

/e/, /a/, /o/, and /u/ (from left to right).

Figure 4: A model of the human vocal tract with a flexible

tongue and a movable mandible.

The picture in Fig. 3 shows a set of vocal-tract

models called VTM-T20 (Arai, 2016). When glottal

sounds are fed into the bottom end of each tube,

different vowels can be heard from the top end. While

the shape of the vocal tract mainly determines what

vowel sound is produced (i.e., “articulation”), the

glottal sound mainly determines the pitch (height) of

the voice and the voice quality. Thus, vocal tracts act

as resonators, and their shapes produce different

speech sounds.

A real vocal tract changes its shape in time.

Therefore, our model in Fig. 4 has a flexible tongue

and a movable mandible (Arai, 2020). By

manipulating the tongue configuration and adjusting

the jaw opening, we can produce different speech

sounds dynamically with this model.

3 SPEECH CHAIN IN DIGITAL

ERA

Thus, the speech chain describes how the human

speech communication system works as each event is

connected as a chain. The original speech chain

shows us a simple situation, but it can be extended to

many scenarios. When we talk on a telephone

network, acoustic signals are fed into the telephone,

converted into electric signals, and transmitted over

the network. In human-computer communication, the

speaker can be a speech synthesis system, or the

listener can be an automatic speech recognition

system. A speech synthesis system can improve the

quality of life of people who have lost the ability to

talk, and an automatic speech recognition system can

be a great help to people who have impaired hearing.

In the following section, I will explain the “My

Voice” project that I was involved with a patient as

an example of a speech chain in the digital era.

3.1 What Is My Voice?

We lose our voice for various reasons, such as

amyotrophic lateral sclerosis (ALS). When an ALS

patient has difficulty breathing, they may receive a

tracheotomy, which causes the patient to lose the

ability to speak. A laryngectomy is another procedure

that causes people to lose their voice. “My Voice” is

free, widely used Japanese speech synthesis software

that gives patients the ability to use their voice after

surgeries that take away their ability to speak.

My Voice is widely used for a few reasons in

particular. First of all, it is free. Also, it is easy to use.

The recording time can be minimized for patients and

reduce their workload, as the main recording is only

for basic Japanese syllable units and words can be

concatenated from the recorded syllable units.

Furthermore, its software GUI is well-designed, so a

patient’s therapist, family members, and friends can

also use it with simple training. By recording words

and/or phrases before surgery, patients can keep

communicating using their voice with technology

even after losing that ability physically.

3.2 Why My Voice?

Commercial speech synthesizers usually aim for

clarity and intelligibility in synthesized speech

sounds. However, My Voice uses a speaker’s voice

and vocal characteristics. When an ALS patient has

difficulty breathing as their disease progresses, they

must choose to have a tracheotomy and lose their

What Is a Speech Chain and How Can This Concept Be Applied to the Various Areas of Speech Communication in an Intelligent Society?

voice or gradually lose the ability to breathe

altogether. My Voice gives them the option to have a

tracheotomy and continue using their voice.

4 CONCLUSIONS

We reviewed the speech chain concept and the speech

production mechanism by using a set of vocal-tract

models. After extending the speech chain concept

into the digital era through various forms of speech

communication, we discussed its application to an

intelligent society through our “My Voice” project.

Even though society is becoming increasingly

intelligent and speech communication is evolving

over time, speech communication itself will always

exist because it is a part of being human. One of the

United Nations’ Sustainable Development Goals

(SDGs) is about health and well-being (UNs, 2019).

We need to explore speech communication more and

develop more applications for sustainable societies.

Our vocal-tract models are also used to test the

airstream of human breath and droplets from

producing speech. One way to visualize the aerosol

and the droplets from speech production is by passing

a laser sheet over a human speaker. However, a laser

beam can damage human beings, and therefore, our

vocal-tract models are now being used to simulate our

speech communication (Arai, 2021). It is also another

way of contributing our technology towards the SDG

goals.

ACKNOWLEDGEMENTS

I would like to thank the organizers of the conference

for inviting me. I would also like to thank the people

involved in the My Voice project (especially Kenji

Fujimoto and his family members), Takaki

Yoshimura, Musashi Homma, and Shigeto

Kawahara, and members of Arai Laboratory (Sophia

University). This work was partially supported by

JSPS KAKENHI Grant Numbers 18K02988 and

21K02889.

REFERENCES

Arai, T. (2007). ‘Education system in acoustics of speech

production using physical models of the human vocal

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201.

Arai, T. (2012). ‘Education in acoustics and speech science

using vocal-tract models’. The Journal of the

Acoustical Society of America 131(3) 2444–2454.

Arai, T. (2016). ‘Vocal-tract models and their applications

in education for intuitive understanding of speech

production’. Acoustical Science and Technology 37(4)

148–156.

Arai, T. (2020). ‘Two different mechanisms of movable

mandible for vocal-tract model with flexible tongue’.

Proc. of INTERSPEECH 1366–1370.

Arai, T. (2021). ‘Vocal-tract models to visualize the

airstream of human breath and droplets while producing

speech’. Proc. of INTERSPEECH.

Denes, P. B, and Pinson, E. N. (1993). The Speech Chain:

The Physics and Biology of Spoken Language, 2nd

edition, W. H. Freeman, New York.

Kawahara, S., Homma, M., Yoshimura, T., and Arai, T.

(2016). ‘My Voice: Rescuing voices of ALS patients’.

Acoustical Science and Technology 37(5) 202–210.

United Nations. (2019). The Sustainable Development

Goals Report, https://doi.org/10.18356/55eb9109-en.

ICE-TES 2021 - International Conference on Emerging Issues in Technology, Engineering, and Science