Acoustic and Physiological Phonetics

1. Acoustic and Physiological Phonetics Vowel Production and Perception Stephen M. Tasko

2. Learning Objectives • Review source-filter theory and how it relates to vowel production • Distinguish between source spectrum, transfer function and output spectrum. • Calculate formant/resonant frequencies of a uniform tube based on its physical dimensions. • Describe how the area function of an acoustic resonator is determined. • Distinguish between and describe relation between area function and transfer function. Stephen M. Tasko

3. Source Filter Theory Speech (What We Hear) Filter (Resonator) Source (Phonation) Frequency Response Curve (Transfer Function) Input Spectrum Output Spectrum Stephen M. Tasko

4. Same Source, Different Filter Stephen M. Tasko

5. FRC peaks – resonant or formant frequency Tube resonators have an infinite number of formants F1, F2, F3 … denotes formants from low to high frequency Frequency response curve/Transfer Function F1 F2 F3 F4 Stephen M. Tasko

6. Vocal tract as a tube • Tubes have physical characteristics (shapes) • Tubes act as acoustic resonators • Acoustic resonators have frequency response curves (FRC), also known as ‘transfer functions’ • Tube shape dictates the frequency response curve. Stephen M. Tasko

7. The vocal tract shape during vowel production • Can be (roughly) uniform in shape • The vocal tract is fairly uniform in its cross-sectional diameter for neutral or central vowel (schwa) • Can also be take on non-uniform shapes • Are observed for non-neutral vowels • Have a more complex geometry • Does not allow simple calculations of formants • Formant values are derived from the vocal tract area function Stephen M. Tasko

8. Vocal tract as a tube Straight tube, closed at one end, with a uniform cross-sectional diameter Straight tube, closed at one end, of differing cross-sectional diameter Vocal tract: bent tube, closed at one end, with differing Cross-sectional diameter. Stephen M. Tasko

9. What is an area function? … Area (cm2) Length along tube (cm) Stephen M. Tasko

10. Area (cm2) Length along tube (cm) Area function of a uniform tube • Area function dictates the frequency response curve for that tube Stephen M. Tasko

11. Vocal Tract Area Function Stephen M. Tasko

12. Vocal Tract Area Function Stephen M. Tasko

13. Relationship between vocal tract shape, the area function and the frequency response curve FRC Stephen M. Tasko

14. Key points • Vocal Tract has a variable shape, therefore • It is a variable resonator • Can have a variety of area functions • Can generate a variety of frequency response curves • A given area function can lead to one (and only one) frequency response curve • A given frequency response curve and arise due to a variety of different area functions Stephen M. Tasko

15. Learning Objectives • Describe the basic shape of the area function for the four corner vowels. • Describe F1-F2 relations for English vowels with specific emphasis of the corner vowels • Draw and recognize (1) wide band spectrograms, (2) spectrum envelopes, and (3) frequency response curves for the corner vowels • Draw and interpret various plots that relate formants values for English vowels. • Outline our basic tongue and lip rules for predicting formant shifts from the neutral position. Stephen M. Tasko

16. Vowels: Articulatory Description Stephen M. Tasko

17. Vowels: Articulatory Description • Degree of lip rounding • Rounded • Unrounded • Degree of tension • Tense • Lax Stephen M. Tasko

18. “Neutral” Configuration Vocal Tract Area Function Articulatory Configuration/ Vocal Tract Shape Frequency Response Curve Stephen M. Tasko

19. Low back vowel Vocal Tract Area Function Articulatory Configuration/ Vocal Tract Shape Frequency Response Curve Stephen M. Tasko

20. High back rounded vowel Vocal Tract Area Function Articulatory Configuration/ Vocal Tract Shape Frequency Response Curve Stephen M. Tasko

21. Low front vowel Vocal Tract Area Function Articulatory Configuration/ Vocal Tract Shape Frequency Response Curve Stephen M. Tasko

22. Relationship between vocal tract shape, the area function and the frequency response curve Vocal Tract Area Function Articulatory Configuration/ Vocal Tract Shape Frequency Response Curve Stephen M. Tasko

23. Resonant (formant) Frequency F1, F2 frequency are particularly important F3 frequency plays a smaller role Landmark study: Peterson and Barney (1952) What distinguishes vowels in production and perception? Stephen M. Tasko

24. Vowels: Spectrographic Patterns Stephen M. Tasko

25. Vowels: Frequency Response Curve Patterns Mid Central vowel F1: 500 Hz F2: 1500 Hz /i/ Gain /u/ // // Stephen M. Tasko frequency

26. /i/ & /u/ have a low F1 // & // have high F1 Tongue height ~ F1 Tongue height  F1  Tongue height  F1  /u/ & // have low F2 /i/ & // have high F2 Tongue advancement ~ F2 Tongue front F2  Tongue back F2  Observations Stephen M. Tasko

27. Learning Objectives • Outline the key assumptions and parameters of the Stevens & House (SH) articulatory model of vowel production. • Describe the acoustic consequences of changing SH model parameters. • Provide acoustic explanations for how (1) the SH model parameters influence area function and (2) how these area function changes influence acoustic (i.e. formant values) • Compare the shape of the vowel quadrilateral and the F1-F2 plot Stephen M. Tasko

28. “Connecting the dots” How do articulatory processes “map” onto acoustic processes? Stephen M. Tasko

29. Model assumes No coupling with Nasal cavity trachea & pulmonary system 3-parameter model (Stevens & House, 1955) Stephen M. Tasko

30. Model parameters Distance of major constriction from glottis (d0) Radius of major constriction (r0) Area (A) and length (l) of lip constriction A/l conductivity index 3-parameter model (Stevens & House, 1955) Stephen M. Tasko

31. 3-parameter model (Stevens & House, 1955) Stephen M. Tasko

32. Key Goal of Study • Evaluate the effect of systematically changing each of these three “vocal tract” parameters on F1-F3 frequency Stephen M. Tasko

33. General Observations Stephen M. Tasko

34. General Observations Stephen M. Tasko

35. General Observations Stephen M. Tasko

36. Interpretation: Double Helmholtz Resonator Model Back Cavity Volume influences F1 Larger volume = lower F1 Smaller volume=higher F1 Front Cavity Volume influence F2 Larger volume= lower F2 Smaller volume=higher F2 Radius of Conduit (r0) influences F1 Larger radius = higher F1 Smaller radius=smaller F1 Back Cavity Front Cavity Major Constriction (ro) Stephen M. Tasko

37. ∆ d0 = ∆Vfront & Vback ↑ d0 =↓ Vfront = ↑F2 ↑ d0 =↑Vback = ↓ F1 Interpretations Stephen M. Tasko

38. ↓ r0 =↓ F1 ↑ r0 =↑F1 When d0 ↑(anterior) ↓ r0 =↓ Vfront= ↑F2 Interpretations ↑lip rounding = ↓A/l = ↓ F1 & F2 Stephen M. Tasko

39. Another way to look at the data (Minifie, 1974) Stephen M. Tasko

40. Articulatory Acoustic Comparisons F1-F2 Plot adjusted to reflect ‘articulatory’ space Traditional F1-F2 Plot + d0 - r0 + - Stephen M. Tasko

41. Learning Objectives • Provide an explanation for why we treat women’s, men’s and children’s vowels as equivalent even though absolute values of formants differ a lot. Stephen M. Tasko

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43. “normalizing” formant values Stephen M. Tasko

44. Clinical Example Stephen M. Tasko

45. Acoustic variables related to the perception of vowel quality • F1 and F2 • Other formants (i.e. F3) • Fundamental frequency (F0) • Duration • Spectral dynamics • i.e. formant change over time Stephen M. Tasko

46. How helpful is F1 & F2? From Hillenbrand & Gayvert (1993) Stephen M. Tasko

47. How does adding more variables improve pattern classifier success? • F1, F2 + F3 • 80-85 % • F1, F2 + F0 • 80-85 % • F1, F2 + F3 + F0 • 89-90 % Stephen M. Tasko

48. Nearby vowels have different durations How about Duration? Stephen M. Tasko

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50. What about Duration? Stephen M. Tasko