A comparative acoustic study of hanoi vietnamese and general american english monophthongs

Vietnam national university, Hanoi
University of languages and international studies
Faculty of Post graduate studies
DON MINH MO

A comparative acoustic study of Hanoi
Vietnamese and general American
English monophthongs
Phân tích âm học so sánh hệ thống nguyên âm đơn Tiếng Việt Hà Nội và tiếng Anh
Mỹ Phổ thông

A thesis submitted to the Faculty of Post Graduate Studies,
University of Languages and International Studies, VNU, Hanoi
in partial fulfillment of the requirements for the degree of
Master of Arts
in
English Linguistics
Code: 60.22.15

HA NOI 2012

i


Vietnam national university, Hanoi
University of languages and international studies
Faculty of Post graduate studies
DON MINH MO

A comparative acoustic study of Hanoi
Vietnamese and general American

English monophthongs
Phân tích âm học so sánh hệ thống nguyên âm đơn Tiếng Việt Hà Nội và tiếng Anh
Mỹ Phổ thông

A thesis submitted to the Faculty of Post Graduate Studies,
University of Languages and International Studies, VNU, Hanoi
in partial fulfillment of the requirements for the degree of
Master of Arts
in
English Linguistics
Code: 60.22.15
Supervisor: Pham Xuan Tho, M.A.

HA NOI 2012

ii


LIST OF TABLES
Table

1

Title

The first and second formant frequencies of all the subjects for

Page

34

each vowel.

2
3

The values of the first and the second token of each sound 47
produced by each speaker.
The average values of F1 and F2 for each vowel as spoken by
53
ten speakers

vi


LIST OF FIGURES
Figure

Title

Page

1

The spectrogram of the author’s pronunciation of [i] in hi

18

2

The effect of [ɲ] on [i] in inh and nhi, as produced by the
researcher.
The effect of [ɲ]on [a] in nha

34

The difference between the vowel in e and anh, produced by a
subject.
The difference between the vowel in e and anh,
produced by another subject.
The similarities between the vowel in anh and ay,
produced by a subject.
The similarities between the vowel in anh and ay,
produced by another subject
Spectrograms of [ɤ]and [ɤ̆n ]
Spectrograms of [ɤn], on the left, and [ɤ̆ n], on the right
The similarities between the vowel in a [a] and ay [ăi],
produced by a subject. The spectrogram of [a] is on the
left, and of [ăi] is on the right.
The duration of [a] and [ă] in ai, on the left, and ay, on
the right.
The correlation between the two measurements of each F1 and
F2 by the first 4 subjects.
The monophthongs of ten speakers of Vietnamese in Hanoi
dialect
The formant chart showing the average values of F1 and F2
for each monophthong as spoken by ten speakers
A formant chart showing the formant frequency F1 and F2 for
eight English monophthongs. The scales are marked in Hz,
arranged at Bark scale intervals

The formant chart of Vietnamese monophthongs produced by
female speakers

38

The formant chart of General American English monophthongs
produced by female speakers

58

3
4
5
6
7
8
9
10

11
12
13
14
15
16
17

36

38

39
39
41
42
44

45
50
53
54
56
57

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TABLE OF CONTENTS
STATEMENT OF AUTHORSHIP ................................................... i
ABSTRACT ................................................................................... iv
ACKNOWLEDGEMENT ................................................................ v
LIST OF TABLES ......................................................................... vi
LIST OF FIGURES ....................................................................... vii
TABLE OF CONTENTS .............................................................. viii
Chapter 1: INTRODUCTION .......................................................... 1
1.

Rationales ................................................................................................................... 1

2.

Scope of the research and the research questions ................................................... 3

Chapter 2: THE REVIEW OF LITERATURE ................................. 5
2.1. The articulatory description of Hanoi Vietnamese monophthongs ....................... 5
2.2 The acoustic description attempts ............................................................................ 10
2.3. Characterizing vowel qualities with the acoustic properties ................................ 16
2.4 General American English ........................................................................................ 24
2.4.1 The traditional description ................................................................................ 24
2.4.2 The acoustics of GA ........................................................................................... 27

Chapter 3 RESEARCH METHODOLOGY .....................................30
3.1 The subjects ............................................................................................................... 30
3.2 The stimuli ................................................................................................................. 30
3.3 The recording process ............................................................................................... 31
3.4 The analysis process .................................................................................................. 32

Chapter 4: FINDINGS AND DISCUSSION ..................................34
4.1 The acoustics of Hanoi Vietnamese monophthongs .............................................. 34
4.1.1 [ɛ̆] and [ɛ] .......................................................................................................... 35
4.1.2 [ɤ] and [ɤ̆] ........................................................................................................... 40
4.1.3 [a] and [ă] ............................................................................................................ 43

viii


4.1.4 Regression analysis ............................................................................................ 48
4.1.5 Charting the formants of Hanoi Vietnamese monophthongs ........................ 51
4.2 The monophthongs of Hanoi Vietnamese and General American English in
comparison ....................................................................................................................... 58

Chapter 5 CONCLUSION ..............................................................62
5.1. The main findings on the acoustics of Hanoi Vietnamese monophthongs ......... 62
5.2 The monophthongs of Hanoi Vietnamese and General American English in
comparison ....................................................................................................................... 63
5.3 The limitations of the study and suggestions for further research. ...................... 64

REFERENCES ...............................................................................66
Appendix 1: Phiếu chấp thuận tham gia vào nghiên cứu ...................................................... 68

Appendix 2: The stimuli ........................................................................ 69

ix


Chapter 1: INTRODUCTION
1. Rationales
The ultimate aim of this research is to achieve a cross language
comparison between the acoustic properties of Hanoi Vietnamese
monophthongs and General American English monophthongs. The
findings of the accomplished study are significant, from both the
linguistic and pedagogical perspectives.
Ladefoged states firmly that, “The best way of describing vowels is
not in terms of the articulations involved, but in terms of their
acoustic properties.” (2003, p.104). A considerable amount of space
of this thesis is devoted to the researcher’s analysis of the
monophthongs, or pure vowels (Wells, 1962, p.1) of Vietnamese,
Hanoi dialect. Aside from a few studies conducted overseas, which
have important limitations to be addressed, which are discussed in
details in the Review of Literature of this thesis, there has been no
attempt to study the vowel acoustics of the recognized standard

Vietnamese so far.
The literature on Vietnamese vowel acoustics has been mainly
concerned with the description of the sounds from the views of
articulatory phonetics. The investigations conducted by Nguyễn
(1998), and Đoàn (2000) are typical examples. These studies
examined the behaviors of the vocal organs involved in the
articulatory process when a particular sound is being produced. This
method, while having the advantage of being straightforward, has put
1


forwards ideas which remain an approximation to the truth.
Ladefoged and Johnson (2011, p.197) comment,
Traditional articulatory descriptions are often not in accord with
the actual articulatory facts. For well a hundred years,
phoneticians have been describing vowels in terms such as high
versus low and front versus back. To some extent, they have been
using these terms as labels to specify acoustic dimensions rather
than as descriptions of actual tongue positions. Phoneticians are
thinking in terms of acoustic fact, and using physiological fantasy
to express the idea.

Acoustics offers sufficient tools for explaining the vowel qualities.
The production of a speech sound involves firstly the vibration of the
vocal cords, which produces sound waves. It involves secondly the
performance of the vocal tract, which can be changed into various
shapes, as a filter, under the acoustic impedance. Vowel sounds are
characterized acoustically by formants, which are frequency regions
of high energy concentration corresponding to the pass bands of the
throat and mouth cavities (Wells, 1962, p.1).Therefore, instead of

only studying a particular sound from the outside, rather
subjectively, by observing with eyes, trying to set up a collection of
its articulatory features, there should be a rigorous description
method where every dimension of a sound as its nature is measured
and displayed objectively on the screen of an electronic device.
The analysis, carrying out appropriately, would result in an acoustic
vowel chart, representing accurately the linguistic aspects of Hanoi
2


Vietnamese monophthongs, which serves as a valuable source of
reference for cross language comparison.
The pronunciation of General American English and of Hanoi
Vietnamese are acknowledged as the reference accents of English
and Vietnamese respectively. As a result, from the pedagogical
aspect, the findings of the research are of highly practical values in
teaching the pronunciation of one language to learners of the other
language.
2. Scope of the research and the research questions
The study first examined the quality of the pure vowels in Hanoi
Vietnamese. The frequencies of each of the first two formants of
each monophthong (F1, F2) were investigated on the acoustic
spectrographs, generated from the speech analyzer program PRAAT.
The results obtained from the analysis were then compared with the
results of a recent research

in the monophthongs of General

American English, conducted by Clark, M. J, Hillenbrand, J, et al.
(1995).

The research is aimed at answering two questions:
1) What are the acoustic properties characterizing Hanoi Vietnamese
monophthongs?

3


2) What are the common and distinctive features between the
relative positions of the monophthongs in Vietnamese and General
American English on the formant charts?

4


Chapter 2: THE REVIEW OF LITERATURE
2.1. The articulatory description of Hanoi Vietnamese
monophthongs
There have been considerable attempts to give a description of the
vowel system of Hanoi Vietnamese, impressionistically and
acoustically. This part of the review of literature is concerned firstly
with the set of Vietnamese monophthongs in Hanoi dialect, the
description of which has generated a great amount of debate among
phoneticians. I shall then give an examination of the second set,
being described with fair consistency.
As mentioned above, the vowel inventory of Vietnamese includes
some monophthongs that have been described consistently in the
literature; they also have transparent orthographic representation:
i/i/, u/u/, ô/o/, o/ɔ/, ê/e/, e/ε/, a/a/. However, for some other
monophthongs, orthographically realized by ư, ơ, â, and ă, there are
important conflictions in description. For example, Lindau (1978), as

cited in Matt (2009) describes ư as high back unrounded, while
Thompson (1965) insists that it is high central unrounded, or as and
high central, as proposed by Pham (2003). Hwa-Froelich (2002), as
cited in Matt (2009), puts forward the suggestion that ư that includes
/ɯ/ and /ʊ/, is characteristically employed to denote a high back
unrounded and a lower-high back rounded vowel, respectively.
Lindow (1978) has identified ơ as being back unrounded, /ɤ/ or /ʌ/,
while according to Thompson (1965), it should be represented by /ə/.
5


According to Matt, Alina, and Alison (2009) there are two reasons
for the inconsistency in the description of ư and ơ. Firstly, the
acoustic distinction between lip-rounding and the backness of the
tongue is not clear. The traditional analysis of spectrogram cannot
convincingly differentiate the characteristics because of the almost
similar, or even equal acoustic properties (Ladefoged, 2011). The
second reason is the different goal behind the phonetic and
phonological descriptions of the vowels concerned. Phonetic
descriptions, the goal of which is to provide a description of the
vowels’ features as being realized in spoken speech, are concerned
with the articulatory or acoustic features of the vowels. Phonological
descriptions, on the other hand, are concerned with the vowels’
structure and function in relation to each other in a system.
Naturally, different goals of the studies conducted have resulted in
the inconsistency.
As mentioned earlier, there are two other Vietnamese vowels, which
have been identified with conflicting features. The vowels realized
by â and ă are traditionally described as “short”, low central.
However, there has been a great amount of debate surrounding

whether these vowels are short counterparts of ơ and a respectively,
which are long vowels of similar quality, or they are short vowels
with distinct vowel qualities. One of the ultimate goals of the current
study is to provide a systematic description of the quality of Hanoi
Vietnamese pure vowel inventory; therefore, it shall not be
concerned with the vowel duration.
6


Thompson (1965) is among the references of highest citation
frequency. In his rather comprehensive account of the Vietnamese
language, a fine amount of space has been devoted to the vowel
system of Hanoi dialect.
According to Thompson (1965), the dialect’s vocalic system consists
of two sub-systems of upper vocalics, which includes six vowels and
three semivowels, articulated relatively high in the mouth, and lower
vocalics, which includes five vowels and one semivowels, articulated
relatively low. The table below gives further details on this.

The Vocalic System, Thompson (1965, p.12)

It can be made clearer from this table what Thompson (1965) has
illustrated. The upper vocalics includes three positions, being
relatively distinctive from each other: front, back unrounded, and
back rounded. A high vowel, an upper-mid vowel, and a semivowel
occupy each of the positions. He emphasizes that there are no vowels
7


that occur at the final position. Further description of the upervocalics vowels are provided as follows.

/i/ is proposed here as a high front or central unrounded vowel. It is
lower high central before final ch, nh, as in ích, be useful, and lính,
soldier. Before ê, p, m in the same syllable, it is an upper high front
vowel. Examples are provided as in biết, miệng, kíp, tìm, which
means know, mouth, be urgent, and search for respectively. It is
lower high front elsewhere in the same syllable.
/e/ is characterized as being upper mid front or central, unrounded. It
is upper mid central before final ch, nh; and after [i] before [w, p, m,
t, n] in the same syllable, which is “slightly lower before [w]” (p.30).
Examples given include ếch, bênh, hiểu, tiếp, which respectively
means frog, defend, understand, and receive in English. The vowel is
upper-mid front elsewhere.
/u/ is described as a high back rounded vowel. Thomson (1965)
emphasizes that “it tends to be upper high, but only before [m] and
[p]” (p.31), as in chụp (seize suddenly), chum (earthenware jar), and
it will be lower high elsewhere, as in núi, (mountain), mũ, (hat), tuổi,
(age).
/o/ is identified as being upper mid back rounded. It is higher mid
before [j, w], as in tôi, (I), rồi, (be already accomplished), cô, (aunt),
lỗ, (hole), and is mid strongly centralized after [u], as in buồn, (be

8


sad), quốc, (country), tuổi, (age), chuột, (rat). Finally, it is upper mid
elsewhere, that is, before [p, m, t, n].
/ε/ is proposed to be lower mid front unrounded. There is little
variation when the sound is realized in different contexts.
/ɔ/, is much like that of /ε/, maintaining its quality when being
distributed differently. The vowel is described as lower mid back

rounded.
/a/ is characterized as a lower low front unrounded vowel.
Đoàn (2000) has proposed the largest vowel inventory of
Vietnamese, with thirteen monophthongs, including /i/, /e/, /ɛ/, /ɛ̆/,
/ɯ/, /u/, /o, /ɔ/, /ɔ̆/, /ɤ/, /ɤ̆/, /a/, and /ă/. The author did not attempt to
describe these vowels in terms of how they are articulated, as
articulatory phoneticians have often done. Instead, qualities of all the
vowels are described firstly in terms of their timbre. The timbre is
then explained as being high (bổng), mid-low (trầm vừa), and low
(trầm). The table below illustrates how Vietnamese monophthongs
are distinguished from each other in terms of their timbre, according
to the author. (p.191)
-

High category: /i, e, ɛ, ɛ̆/

-

Mid-low category: /ɯ, ɤ, ɤ̆, a, ă/

-

Low category: /u, o, ɔ, ɔ̆/

9


However, it is not clear from the explanation what the vowels are
high, mid-low, and low in terms of. If that is concerned with pitch,
there appears to be confusion between the vowel quality and the

pitch at which they are produced. Acoustic studies of vowels have
demonstrated that the pitch of vowels, as perceived by listeners, is
decided by the fundamental frequencies of the sound waves
producing that vowel (F0), and has practically no effect on the vowel
quality.
There are four pairs of Vietnamese vowels, which according to the
study, differentiated by duration. These include /ɛ̆/ and /ɛ/, /ɔ̆/ and
/ɔ/, / / and /ă/, /ɤ/ and /ɤ̆/. It is maintained that these four
pairs of vowel have the same quality, and are in long-short
opposition. (p.195)
2.2 The acoustic description attempts
Matt et al. (2009) carried out an exploration of the Vietnamese
monophthongs produced by a small group of native speakers from
both northern and southern Vietnam. The researchers also attempted
to provide a comparison between the native production and those
made by American adult learners. The goals of the study are
significant. The method of conducting the study, however, is
problematic. In order to eliminate the anatomical differences among
participants, the normalization method inspired by Watt and

10


Fabricious (1973) has been employed in the study. This method has
been severely attacked by modern phoneticians.
Johnson (2005) pointed out that, “Talkers may differ from each other
at the level of their articulatory habits of speech. This, in itself,
would suggest that perception may not be able to depend on vocal
tract normalization to “remove” talker differences by removing vocal
tract differences” (p.19). Johnson et al. (1993) goes further:

The presence of individual differences in speech production also
complicates matters for vocal tract normalization. Though normalization
research has usually focused on male/female differences in vocal tract size
and shape, vocal tracts - even within genders - come in lots of different
sizes and shapes. Talkers apparently adopt different (possibly arbitrarily
different) articulatory strategies to produce the “same” sounds.

Thus,

accurate recovery of the talker’s articulatory gestures would not
completely succeed in “normalizing” speech. (P.20)

The second problem of the method is in its scale. The study was
conducted on too small a scale so as to provide a conclusive support
for the researchers’ claims in the discussion of the findings.
According to the researchers,
Native speaker participants included 3 Northern dialect speakers (1 female,
2 males) and 1 Southern dialect speaker (female). All were originally from
Vietnam and had been living in an English-speaking country for 6 to 26
years. They ranged from 42 to 64, and all had experience teaching
Vietnamese as a foreign language to adults.

11


Firstly, the number of participants selected is too small, and is
therefore statistically insignificant. This can be attributed to the
authors’ reliance on the normalization method adopted, as mentioned
before. Secondly, while the qualities of Vietnamese vowels have
been recognized as being substantially varied from dialect to dialect

in realization, there is no indication that the subjects were screened
for dialect, and very little information is provided about the dialects
of the speakers. The present research represents the researcher’s
attempt to address these limitations. (see Chapter 3 for further
details)
Srihari and Nguyen (2004) is another attempt to describe the
Vietnamese vowel characteristics employing spectrograms analysis.
In order to make decision on the set of vowels for the recording
process, the authors follow the work of Thompson (1965, 1987),
closely, claiming that there are eleven monophthongs in the
Vietnamese vowel system (Hanoi dialect), which are /i, ɯ, u, e, γ, o,
ε, ɔ, ɐ, a, ɑ

12


The vocalics systems (Thompson, 1987, as cited in Srihari and Nguyen, 2004)

Making a comparison with the system that Mai, Vu, and
Hoang (2008) proposed, considerable differences could be
spotted. In the latter account, it is suggested that there are 13
pure vowels in the system, and noticeably, there is not an
existence of /ɑ/, characterized as a low, back, unrounded
vowel, as Srihari and Nguyen (2004) maintain. In addition,
these authors support the claim that /γ, o, ε/ have three
counterparts differing just in terms of duration, which are /ɤ̆/, /ɔ̆/,
and /ɛ̆/. This is a part of the inconsistent description of the
Vietnamese vowel inventory, as mentioned earlier. Even Thompson
(1987) has departed from his previous proposal made in Thompson
(1965), with regards to the existence of /ɑ/. As a result, deciding on

a set of eleven monophthongs has posed a threat to the validity of the
findings.
The aims of the study, as stated by its author, are to provide “a
preliminary quantitative description of formant values for F1 and F2
for each vowel and plot the vowel chart of Vietnamese.” (p.2).
However, what has made it even more problematic, again, is the
scale of the research. The subject of the study, as described, is “a 24year-old native male speaker of Hanoi dialect, the standard dialect of
Vietnam. The speaker can speak English fluently but not well-trained
in phonetics.” (p.2). This problem also occurred in the previous
13


study. There are anatomical differences among speakers of a certain
language; therefore, selecting one subject for examination would not
provide findings which are representative of the population. Given
that the author would carry out an analysis on the qualitative aspects
of the vowels in question, the conclusion on the acoustics of the
vowels of a language being drawn from the analysis of the recording
of a single speaker of it is seriously questionable. Ladefoged (2003)
pointed out that, “The fact that data has been measured correctly does
not show that there are no problems with the speakers. When looking
at the formants of a group of people you should check whether any
one speaker is different in any way from the others.” (p.129)

The vowels of five speakers of Banawa, Ladefoged (2003, p.129)

14


The ellipse in the figure encloses four stressed [e] vowels of a

speaker. As can be seen, the first formant values of his [e] are
distinct from those of the other speakers. This speaker, therefore, has
produced this sound in a way that is significantly different from the
others. This deviation, according to Ladefoged (2003), cannot be
ascribed to some anatomical factor such as a very small vocal tract
size. This is because the other vowels produced by him are similar to
those made by the rest of the speakers. The author’s suggestion is
that, “if you find a speaker who pronounces a word in a significantly
different way, you should leave this part of the data out when
providing diagrams of the vowel qualities of the language, noting,
however, that there are speakers who deviate from the general
pattern.” (p.129).
The second problem with the currently reviewed study involves the
set of words containing the vowels chosen for recording.

The word list containing the vowels in question, Srihari and Nguyen (2004, p.3)
15


The /t-/ context is not the best choice.

According to Ladefoged

(2011, p.199), a stop closure will cause the vowel’s first formant
(F1) to rise from a low position. As a result, the accuracy of the
formant values calculated might be affected. It is suggested in a
number of the studies (James et al., 1995; Broadbent & Ladefoged,
1957; Wells, 1962; Ladefoged, 2011) that a word list of the /h-d/
context would provide the best spectrograms, as /h/ has almost no
effect on the formants of the adjacent vowels in the same syllable.

2.3. Characterizing vowel qualities with the acoustic properties
The current study is inspired by Ladefoged’s (2003) firm statement
that, “the best way of describing vowels is not in terms of the
articulations involved, but in terms of their acoustic properties.”
(p.104). In this section we shall take a closer look at the acoustics of
vowels.
The different sounds of language are physically characterized with
four dimensions, which are the fundamental frequency, the
amplitude, the duration, and the formants distribution of the sound
wave. The four corresponding perceptual dimensions are pitch,
loudness, length, and quality.
The current study has not investigated the amplitude and the
fundamental frequency of vowels, being primarily concerned with
the spectral distribution of the pure vowels. The measurements of the
vowel duration have been investigated insofar as they distinguish the

16


pairs of vowels having been described with inconsistency in
articulatory phonetics.
Articulatory phonetics describes how a vowel is articulated, in terms
of the behaviors of the articulators, but there has not been a term to
describe the difference between the quality or timber of one vowel
and another vowel. Among the dimensions of the complex sound
waves produced by the human vocal cords, we need to consider
carefully the spectral distribution of the component frequency. A
speaker can pronounce a vowel on any pitch within the range of his
voice without changing its identity. Ladefoged (2003) provides a
prime example:

I can say the vowels in heed, hid, head, had on a low pitch, when the vocal
folds are vibrating about 80 times a second, and then I can say them again with
vocal folds vibrating 160 times a second. The pitch of my voice will have
changed, but the vowels will still have the same quality. I can also say any
vowel loudly or softly. The quality, the factor that distinguishes one vowel from
another, remains the same when I shout or talk quietly. (p.31)

The differences among vowels are often compared with the different
instruments. The same note can be played on a guitar, a violin, or a
piano. This can be done as the sound is produced at the same rate of
repetition of a special component wave, i.e, the fundamental
frequency. What is interesting here is that, the quality of the music
produced by one instrument will be different from that of any other.
This is due to the differences in the amplitude as well as the
frequency of the component waves. The quality of a vowel differs
17


from that of another in plainly the same way. Irrespective of the
pitch on which a vowel is produced, the quality will stay unchanged.
A popular way that phoneticians describe the acoustics of the human
speech sounds is using the tube models. The current research is
primarily concerned with the monophthongs (of Vietnamese), so the
models can be conveniently summarized as follows.
The air in a bottle will be set vibrating when the body of air at the
top of it is blown across. Naturally, the note that is produced as a
result of blowing the air at the bottle top will depend on the size and
the shape of the bottle. The more the volume of air inside is
increased, the lower will the produced note be. This is due to the fact
that the smaller body of air will vibrate more quickly than that of a

larger one, having a higher frequency of resonance.
When a vowel is being produced, it is the vocal tract that acts like a
bottle, with the size and the shape being constantly altered. If for a
bottle, the air inside is set in vibration when blowing across the air at
the top, for the vocal tract it is the pulses of the air from the vocal
folds. What makes the tract different from the bottle is its very
complex shape, which can be constantly changed due to the
movements of the related organs. Conveniently, phoneticians often
consider the body of air in the throat to be the first tube, and that in
the mouth to be the second one. The resonances of the vocal tract are
called the formants, which correspond to the basic frequencies of the
vibrations of the air in the vocal tract. Therefore, the formants of a
18


sound are the properties that directly depend on the size and the
shape of the tract, both the front and the back part of the cavity. They
are largely responsible for the characteristic quality of the vowel. My
vowel [i] in the Vietnamese word hi is characterized by formants
around 380, 2200, and 3200 Hz.

Figure 1: The spectrogram of the author’s pronunciation of [i] in hi

When my vowel [i] is produced, a damped wave is generated, and
always with these approximate basic frequencies. It is this set of
components that allow us to distinguish [i] from the other vowels.
Each vowel is associated with a different shape of the vocal tract,
resulting in the different component basic frequencies (the formants)
being produced when the body of air inside vibrates.

19