Control Methods Used in a Study of the Vowels
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Control Methods Used in a Study of the Vowels
Relationships between a listener's identification of a spoken vowel and its properties as revealed from
acoustic measurement of its sound wave have been a subject of study by many investigators. Both the
utterance and the identification of a vowel depend upon the language and dialectal backgrounds and the
vocal and auditory characteristics of the individuals concerned. The purpose of this paper is to discuss
some of the control methods that have been used in the evaluation of these effects in a vowel study program
at Bell Telephone Laboratories. The plan of the study, calibration of recording and measuring equipment,
and methods for checking the performance of both speakers and listeners are described.-The methods are
illustrated from results of tests involving some 76 speakers and 70 listeners.
INTRODUCTION
ONSIDERABLE variation is to be found in the processes of speech production because of their
complexity and because they depend upon the past
experience of the individual. As in much of human
behavior there is a self-correcting, or servomechanism
type of feedback involved as the speaker hears his own
voice and adjusts his articulatory mechanisms. 1
In the elementary case of a word containing a conso-
nant-vowel-consonant phoneme 2.3 structure, a speaker's
pronunciation of the vowel within the word will be
influenced by his particular dialectal background; and
his pronunciation of the vowel may differ both in
phonetic quality and in measurable characteristics from
that produced in the word by speakers with other
backgrounds. A listener, likewise, is influenced in his
identification of a sound by his past experience.
Variations are observed when a given individual
makes repeated utterances of the same phoneme. A
very significant property of these variations is that they
are not random in a statistical sense, but show trends
and sudden breaks or shifts in level, and other types of
nonrandom fluctuations. 4 Variations likewise appear in
the successive identifications by a listener of the same
utterance. It is probable that the identification of
repeated sounds is also nonrandom but there is little
direct evidence in this work to support such a con-
clusion.
A study of sustained vowels was undertaken to in-
vestigate in a general way the relation between the
vowel phoneme intended by a speaker and that identi-
fied by a listener, and to relate these in turn to acous-
tical measurements of the formant or energy concentra-
tion positions in the speech waves.
In the plan of the study certain methods and tech-
niques were employed which aided greatly in the
collection of significant data.
tain sequences of observations for the purpose of check-
ing the measurement procedures and the speaker and
listener consistency. The acoustic measurements were
made with the sound spectrograph; to minimize meas-
urement errors, a method was used for rapid calibration
of the recording and analyzing apparatus by means of
a complex test tone. Statistical techniques were applied
to the results of measurements, both of the calibrating
signals and of the vowel sounds.
These methods of measurement and analysis have
been found to be precise enough to resolve the effects
of different dialectal backgrounds and of the non-
random trends in speakers' utterances. Some aspects
of the vowel study will be presented in the following
paragraphs to illustrate the usefulness of the methods
employed.
EXPERIMENTAL PROCEDURES
The plan of the study is illustrated in Fig. 1. A list
of words (List 1) was presented to the speaker and his
utterances of the words were recorded with a mag-
netic tape recorder. The list contained ten monosyllabic
words each beginning with I-hi and ending with I-d]
and differing only in the vowel. The words used were
heed, hid, head, had, hod, hawed, hood, who'd, hud, anal
heard. The order of the words was randomized in each
list, and each speaker was asked to pronounce two
different lists. The purpose of randomizing the words in
the list was to avoid practice effects which would be
associated with an unvarying order.
If a given List 1, recorded by a speaker, were played
back to a listener and the listener wero asked to write
down what he heard on a second list (List 2), a com-
parison of List 1 and List 2 would reveal occasional
LEST
I , • SPEAKER I'---I TAPE I •
RECORDER
II I
MEASURING •-I
Fro, •. Recording and measuring arrangements for vowel study.
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176 ß G. E. PETERSON AND H. L. BARNEY
FiG. 2. Broad band spectrograms and amplitude sections of the word list by a female speaker.
differences, or disagreements, between speaker and
listener. Instead of being played back to a listener,
List ! might be played into an acoustic measuring
device and the outputs classified according to the
measured properties of the sounds into a List 3. The
three lists will differ in some words depending upon the
characteristics of the speaker, the listener, and the
measuring device.
A total of 76 speakers, including 33 men, 28 women
and 15 children, each recorded two lists of 10 words,
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METHODS USED IN A STUDY OF VOWELS 177
making a total of 1520 recorded words. Two of the
speakers were born outside the United States and a few
others spoke a foreign language before learning English.
Most of the women and children grew up in the Middle
Atlantic speech area. 5 The male speakers represented a
much broader regional sampling of the United States;
the majority of them spoke General American. 5
The words were randomized and were presented to a
group of 70 listeners in a series of eight sessions. The
listening group contained only men and women, and
represented much the same dialectal distribution as
did the group of speakers, with the exception that a
few observers were included who had spoken a foreign
language throughout heir youth. Thirty-two of the 76
speakers were also among the 70 observers.
The 1520 words were also analyzed by means of the
sound spectrograph. 6,7
Representative spectrograms and sections of these
words by a male speaker are shown in Fig. 3 of the
paper by R. K. Potter and J. C. Steinberg; 4 a similar
list by a female speaker is shown here as Fig. 2. 8 In the
spectrograms, we see the initial [h• followed by the
vowel, and then by the final ['d•. There is generally a
part of the vowel following the influence of the [h• and
preceding the influence of the [d• during which a
practically steady state is reached. In this interval, a
section is made, as shown to the right of the spectro-
grams. The sections, portraying frequency on a hori-
zontal sca;le, and amplitude of the voiced harmonics on
the vertical side, have been measured with calibrated
Plexiglass templates to provide data about the funda-
mental and formant frequencies and relative formant
amplitudes of each of the 1520 recorded sounds.
LISTENING TESTS
The 1520 recorded words were presented to the group
of 70 adult observers over a high quality loud speaker
system in Arnold Auditorium at the Murray Hill
Laboratories. The general purpose of these tests was to
obtain an aural classification of each vowel to supple-
ment the speaker's classification. In presenting the
words to the observers, the procedure was to reproduce
at each of seven sessions, 200 words recorded by 10
speakers. At the eighth session, there remained five
men's and one child's recordings to be presented; to
these were added three women's and one child's record-
ings which had been given in previous essions, making
again a total of 200 words. The sound level at the ob-
servers' positions was approximately 70 db re 0.0002
dyne/cm 2, and varied over a range of about 3 db at the
different positions.