International Congress Series 1240 (2003) 1277 – 1280

Acoustical analysis of the phonemes /a/, /e/ and /i/ Simone Adad Arau´jo *, Marcos Grellet, Jose Carlos Pereira, Marcelo Oliveira Rosa Rua 20, no. 324, apt. 201, Sector Central, Goiaˆnia-Goia´s, cep 74030-110, Brazil

Abstract With the advance of digital technology, acoustic voice analysis arises as a promising complementary exam to improve diagnostic accuracy in laryngology. This study aims at normatizating acoustic measures including fundamental frequency, perturbation and noise using the Acoustic Voice Analysis Program. The program was developed at the Engineering School of Sa˜o Carlos, University of Sa˜o Paulo. Digital recordings of the phonemes /a/, /e/ and /i/ were obtained in a sample of 80 volunteers living in Ribeira˜o Preto and neighboring areas, from March to August 1997, they produced a total of 240 acoustic signals. The mean values of these measurements were statistically studied regarding sex and phonemes. The authors concluded that most of their results were comparable with those found in the literature. The phonemes /a/, /e/ and /i/ are relevant to acoustic analysis and the phoneme /e/ is the most stable. D 2003 International Federation of Otorhinolaryngological Societies (IFOS). All rights reserved. Keywords: Acoustic measures; Normal voice; Standardization

1. Introduction A voice is a complex event that requires multiple measures, such as perceptual and acoustic evaluations, in order to describe its features. Acoustic analysis is often favored over perceptual evaluation of voice because it is considered objective and it allows us to document the voice and compare the results. Bless [3] states that objective measures help us in achieving information that cannot be provided by human ears or eyes. Thus, the acoustic signs analyses yield an indirect vibratory pattern measurement of the vocal folds. Read et al. [4] reported that with the advance of PC and software, a single system might

* Corresponding author. Tel.: +55-62-2242645; fax: +55-62-2415603. E-mail address: [email protected] (S.A. Arau´jo). 0531-5131/ D 2003 International Federation of Otorhinolaryngological Societies (IFOS). All rights reserved. doi:10.1016/S0531-5131(03)00898-7

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perform various analytical functions and combinations that provide an integrated view of the signal. The purpose of the present study is to evaluate the acoustic analysis of the following phonemes in Portuguese: /a/, /e/ and /i/, using acoustic measures as fundamental frequency, perturbation and noise.

2. Patients and methods The research was carried out at the Clinical Hospital of Ribeira˜o Preto, University of Sa˜o Paulo, from March to August 1997. The sample involved 80 adults, 40 males and 40 Table 1 Acoustic analysis of fundamental frequency, perturbation and noise Sexes Acoustic

Males

Analysis

Phonemes /a/

Fundamental frequency (Fo, Hz) Perturbation Jitter Directional Perturbation Factor (DPF, %) Perturbation Variation Index (PVI, dB) Jitter Ratio (JR, %) Jitter Factor (JF, %) Period Perturbation Quotient (PPQ5, %) Period Perturbation Quotient (PPQ11, %) Shimmer Directional Perturbation Factor (DPF, %) Amplitude Variation Index (AVI, dB) Amplitude Perturbation Quotient (APQ11, %) Noise Spectral Noise Level (SNL, dB) Harmonic to Noise Ratio (HNR, dB) Harmonic to Noise Ratio cepstrum (HNRcepstrum, dB) Normalized Noise Energy (NNE, dB) Breathiness Ratio (BR, dB)

Females Phonemes /e/

/i/

/a/

/e/

/i/

127.61

132.45

142.63

215.42

214.28

226.73

64.90

65.96

65.94

65.54

67.09

68.06

1.16

1.05

1.11

0.76

0.71

1.03

0.37 0.37 0.25

0.36 0.35 0.25

0.32 0.32 0.21

0.85 1.85 0.62

0.67 1.75 0.49

0.31 0.31 0.22

0.30

0.33

0.28

0.67

0.56

0.26

63.77

63.39

64.95

65.17

65.41

65.58

2.37

2.05

1.91

2.52

2.45

1.89

30

17

88.39 1.06

90.04 1.98

1.98

3

36

10

37

92.12 2.30

87.98 1.64

90.29 0.93

91.97 1.54

1.72

1.48

1.63

1.58

1.35

13.08

9.52

9.68

14.40

9.44

10.63

21.54

23.85

24.59

23.54

26.30

27.08

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females, from Ribeira˜o Preto and neighborhood, ages ranging from 20 to 40. All patients had no history of dysphonia, normal vocal folds in videolaryngoscopy, normal voice, which was checked perceptually and had normal hearing. Sustained digital recordings of the phonemes /a/, /e/ and /i/ were made resulting in 240 phonemes registered in a computer using the Acoustic Voice Analyses Program developed by Rosa [5] at the Engineering School of Sa˜o Carlos, from the University of Sa˜o Paulo. The fundamental frequency was obtained using signals processing by cepstrum. The measures studied were Jitter, Shimmer and Noise measures.

3. Results The results were submitted to statistical calculation of their means and standard deviations for each group of phonemes and sexes, by a variance analysis with a significance level ranging from 0.05 to 0.01 (Table 1). The sound wave format was similar between the sexes, as well as the behavior of the perturbation and noise levels existing in the normal voice. In most of the measures taken, the phoneme /e/ was revealed to be the average result between the phonemes /a/ and /i/.

4. Discussion The results show a great variability among the voices, most likely due to individual differences. Our results are consistent with those found by Bielamowicz et al. [2] who compared programs and voice analyses and concluded that there was indeed a divergence, even employing similar measures. Most of the results from the acoustic measures were also consistent with the results found in the international literature, as reported by Arau´jo [1]. We believe that the sound wave format is similar regarding sex. The phoneme /e/ showed an intermediary position between the phonemes /a/ and /i/ due to its intermediary tension and vibration and moderate glottal airflow. On the other hand, the phoneme /a/ reveals less tension from the vocal folds, more vibration and less glottal airflow. As for the phoneme /i/, there is greater tension at the vocal fold, a greater vibration and less glottal airflow.

5. Conclusions The Fundamental frequency and Jitter and Shimmer measurements showed average results similar to those found in the literature. The Jitter measurements produced better perturbation discrimination than the Shimmer measures. The noise measurements also produced good noise discrimination, where the best measurements considered were the Normalized Noise Energy and the Breathiness ratio, which showed more similar results to the literature. The phoneme /e/ was demonstrated to be more stable, whereas the phonemes /i/ and /a/ were shown to be more unstable in most of the acoustic measurements.

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References [1] S.A. Arau´jo, Ana´lise Acu´stica da Voz Normal, Dissertac¸a˜o (Mestrado)-Faculdade de Medicina de Ribeira˜o Preto-Universidade de Sa˜o Paulo, 1999. [2] S. Bielamowicz, J. Kreiman, B.R. Gerratt, M.S. Dauer, G.S. Berke, Comparison of voice analysis systems for perturbation measurement, Journal of Speech and Hearing Research 39 (1996) 126 – 134. [3] D.M. Bless, Measurement of vocal function, Voice Disorders, vol. 24, Otolaryngologic Clinics of North America, 1991, pp. 1023 – 1033. [4] C. Read, E.H. Buder, R.D. Kent, Speech analysis systems: an evaluation, Journal of Speech and Hearing Research 35 (1992) 314 – 332. [5] M.O. Rosa, Ana´lise Acu´stica da Voz para Pre´-diagno´stico de Patologias da Laringe, Dissertac¸a˜o (Mestrado)Faculdade de Engenharia Ele´trica de Sa˜o Carlos-Universidade de Sa˜o Paulo, 1998.