MSU EELE 578 - Control Methods Used in a Study of the Vowels

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THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA VOLUME 24, NUMBER :2 MARCH, 1952 Control Methods Used in a Study of the Vowels GORDON E. PETERSON AND HAROLD L. BARNEY Bdl Talephone Laboratories, Inc., Murray Hill, New Jersey (Received December 3, 1951) 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 •ome 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 œound 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. t In the elementary case of a word containing a conso- nant-vowel-consonant phonemeZ. a 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. s 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. These methods included randomization of test material and repetitions to ob- • Bernard $. Lee, J. Acoust. Soc. Am. 22, 824 (1950). • B. Bloch, Language 24, 3 (1948). a B. Bloch, Language 26, 88 (1950). • R. K. Potter and J. C. Steinberg, J. Acoust. Soc. Am. 26, 807 (1950). 175 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 l-d-] and differing only in the vowel. The words used were heed, hid, head, had, hod, hawed, hood, who'd, bud, and 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 were 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 Fro. 1. Recording and measuring arrangements for vowel study.176 G. E. PETERSON AND H. L. BARNEY hid h•d hird ill. hud I h•d bud hoed had , . I 1 tJ I ' I had hard F•o. 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 1 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,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. • The male speakers represented a much broader regional sampling of the United States; the majority of them spoke General American2 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 their youth. Thirty-two of the 76 speakers were also among the 70 observers. The 1520 words were also


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