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Slide 2 Acoustic and Physiological Phonetics Vowel Production and Perception Stephen M. Tasko Slide 3 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 Slide 4 Source Filter Theory Source (Phonation) Filter (Resonator) Speech (What We Hear) Input Spectrum Frequency Response Curve (Transfer Function) Output Spectrum Stephen M. Tasko Slide 5 Same Source, Different Filter Stephen M. Tasko Slide 6 Frequency response curve/Transfer Function FRC peaks resonant or formant frequency Tube resonators have an infinite number of formants F1, F2, F3 denotes formants from low to high frequency F1F2F3F4 Slide 7 Stephen M. Tasko 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. Slide 8 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 Slide 9 Vocal tract as a tube Vocal tract: bent tube, closed at one end, with differing Cross-sectional diameter. Straight tube, closed at one end, of differing cross-sectional diameter Straight tube, closed at one end, with a uniform cross-sectional diameter Slide 10 Stephen M. Tasko What is an area function? Area (cm 2 ) Length along tube (cm) Slide 11 Stephen M. Tasko Area function of a uniform tube Area function dictates the frequency response curve for that tube Area (cm 2 ) Length along tube (cm) Slide 12 Vocal Tract Area Function Stephen M. Tasko Slide 13 Vocal Tract Area Function Stephen M. Tasko Slide 14 FRC Relationship between vocal tract shape, the area function and the frequency response curve Stephen M. Tasko Slide 15 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 Slide 16 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 Slide 17 Vowels: Articulatory Description Stephen M. Tasko Slide 18 Vowels: Articulatory Description Degree of lip rounding Rounded Unrounded Degree of tension Tense Lax Stephen M. Tasko Slide 19 Neutral Configuration Vocal Tract Area Function Frequency Response Curve Articulatory Configuration/ Vocal Tract Shape Stephen M. Tasko Slide 20 Low back vowel Vocal Tract Area Function Frequency Response Curve Articulatory Configuration/ Vocal Tract Shape Stephen M. Tasko Slide 21 High back rounded vowel Vocal Tract Area Function Frequency Response Curve Articulatory Configuration/ Vocal Tract Shape Stephen M. Tasko Slide 22 Frequency Response Curve Vocal Tract Area Function Low front vowel Articulatory Configuration/ Vocal Tract Shape Stephen M. Tasko Slide 23 Relationship between vocal tract shape, the area function and the frequency response curve Frequency Response Curve Vocal Tract Area Function Articulatory Configuration/ Vocal Tract Shape Stephen M. Tasko Slide 24 What distinguishes vowels in production and perception? Resonant (formant) Frequency F1, F2 frequency are particularly important F3 frequency plays a smaller role Landmark study: Peterson and Barney (1952) Stephen M. Tasko Slide 25 Vowels: Spectrographic Patterns Stephen M. Tasko Slide 26 Mid Central vowel F1: 500 Hz F2: 1500 Hz /i/ /u/ //// //// Gain frequency Vowels: Frequency Response Curve Patterns Stephen M. Tasko Slide 27 Observations /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 Slide 28 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 Slide 29 Connecting the dots How do articulatory processes map onto acoustic processes? Stephen M. Tasko Slide 30 3-parameter model (Stevens & House, 1955) Model assumes No coupling with Nasal cavity trachea & pulmonary system Stephen M. Tasko Slide 31 3-parameter model (Stevens & House, 1955) Model parameters Distance of major constriction from glottis (d 0 ) Radius of major constriction (r 0 ) Area (A) and length (l) of lip constriction A/l conductivity index Stephen M. Tasko Slide 32 3-parameter model (Stevens & House, 1955) Stephen M. Tasko Slide 33 Key Goal of Study Evaluate the effect of systematically changing each of these three vocal tract parameters on F1-F3 frequency Stephen M. Tasko Slide 34 General Observations Stephen M. Tasko Slide 35 General Observations Stephen M. Tasko Slide 36 General Observations Stephen M. Tasko Slide 37 Interpretation: Double Helmholtz Resonator Model Stephen M. Tasko Back Cavity Front Cavity Major Constriction (ro) 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 Slide 38 Interpretations d 0 = V front & V back d 0 = V front = F2 d 0 = V back = F1 Stephen M. Tasko Slide 39 Interpretations r 0 = F1 r 0 = F1 When d 0 (anterior) r 0 = V front = F2 lip rounding = A/l = F1 & F2 Stephen M. Tasko Slide 40 Another way to look at the data Stephen M. Tasko (Minifie, 1974) Slide 41 r0r0 d0d0 - + - + Articulatory Acoustic Comparisons Stephen M. Tasko Traditional F1-F2 Plot F1-F2 Plot adjusted to reflect articulatory space Slide 42 Learning Objectives Provide an explanation for why we treat womens, mens and childrens vowels as equivalent even though absolute values of formants differ a lot. Stephen M. Tasko Slide 43 Slide 44 normalizing formant values Stephen M. Tasko Slide 45 Clinical Example Stephen M. Tasko Slide 46 Acoustic variables related to the perception of vowel quality F1 and F2 Other formants (i.e. F3) Fundamental frequency (F 0 ) Duration Spectral dynamics i.e. formant change over time Stephen M. Tasko Slide 47 How helpful is F1 & F2? Data SourceHuman ListenersPattern Classifier Peterson & Barney (1952) 94.4 %74.9 % Hillenbrand et al. (1995) 95.2 %68.2 % From Hillenbrand & Gayvert (1993) Stephen M. Tasko Slide 48 How does adding more variables improve pattern classifier success? F1, F2 + F3 80-85 % F1, F2 + F 0 80-85 % F1, F2 + F3 + F 0 89-90 % Stephen M. Tasko Slide 49 How about Duration? Nearby vowels have different durations Stephen M. Tasko Slide 50 Slide 51 What about Duration? Stephen M. Tasko Slide 52 What about Duration? Some examples Stephen M. Tasko Slide 53 What about formant variation? Stephen M. Tasko Slide 54 What about formant variation? Stephen M. Tasko Slide 55 Naturally spoken /hAd/ Synthesized, preserving original formant contours Synthesized with flattened formants What about formant variation? Stephen M. Tasko Slide 56 Conclusion: Spectral change patterns do matter. What about formant variation? Stephen M. Tasko Slide 57 What do we conclude? Stephen M. Tasko Slide 58 Sinewave Speech Demonstration Sinewave speech examples (from HINT sentence intelligibility test): Stephen M. Tasko Slide 59 Selected issues that are not resolved What do listeners use? Specific formants vs. spectrum envelope What is the planning space used by speakers? Articulatory Acoustic Auditory Stephen M. Tasko Slide 60 The important role of movement Articulatory movementspectral change Articulatory movement = spectral change Spectral change occurs as speakers transition within and between sound sequences Spectral change plays a significant role in Perception of certain speech sounds Overall speech intelligibility Stephen M. Tasko Slide 61 Diphthongs Slow gliding (~ 350 msec) between two vowel qualities Components Onglide- Onglide- starting point of articulation Offglide- Offglide- end point of articulation Articulatory Transitionformant transition Articulatory Transition = formant transition Diphthongization: articulatory movement within the vowel Varies by geographic region Stephen M. Tasko Slide 62 American English Diphthongs / / - bye / / - bough / / - boy / / - bay / / - bow Stephen M. Tasko