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

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

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

Same Source, Different Filter Stephen M. Tasko 4

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 F1 F2 F3 F4 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. Stephen M. Tasko

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

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

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

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

Vocal Tract Area Function Stephen M. Tasko

Vocal Tract Area Function Stephen M. Tasko

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

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

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

Vowels: Articulatory Description Stephen M. Tasko

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

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

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

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

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

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

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

Vowels: Spectrographic Patterns Stephen M. Tasko

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

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  Stephen M. Tasko

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

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

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

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

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

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

General Observations Stephen M. Tasko

General Observations Stephen M. Tasko

General Observations Stephen M. Tasko

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

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

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

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

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

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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“normalizing” formant values Stephen M. Tasko

Clinical Example Stephen M. Tasko

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

How helpful is F1 & F2? Data Source Human Listeners Pattern Classifier Peterson & Barney (1952) 94.4 % 74.9 % Hillenbrand et al. (1995) 95.2 % 68.2 % From Hillenbrand & Gayvert (1993) Stephen M. Tasko

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

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

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What about Duration? Stephen M. Tasko

What about Duration? Some examples Stephen M. Tasko

What about formant variation? Stephen M. Tasko

What about formant variation? Stephen M. Tasko

What about formant variation? Naturally spoken /hAd/ Synthesized, preserving original formant contours Synthesized with flattened formants Stephen M. Tasko

What about formant variation? Conclusion: Spectral change patterns do matter. Stephen M. Tasko

What do we conclude? Stephen M. Tasko

Sinewave Speech Demonstration Sinewave speech examples (from HINT sentence intelligibility test): Stephen M. Tasko

Selected issues that are not resolved What do listener’s use? Specific formants vs. spectrum envelope What is the “planning space” used by speakers? Articulatory Acoustic Auditory Stephen M. Tasko

The important role of movement 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

Diphthongs Slow gliding (~ 350 msec) between two vowel qualities Components Onglide- starting point of articulation Offglide- end point of articulation Articulatory Transition = formant transition Diphthongization: articulatory movement within the vowel Varies by geographic region Stephen M. Tasko

American English Diphthongs // - “bye” // - “bough” // - “boy” // - “bay” // - “bow” Stephen M. Tasko