Part 1--Acoustics of Consonants

Question 1

Why the Acoustic Theory of Speech Production is Most Accurate for Vowels

Answer 1

For vowels, the resonators can be described as extending from the source (i.e., vibrating vocal folds) to lips within a single tube (i.e., the vocal tract)
For other sound classes, the single tube model is not adequate (e.g., /m/, /n/, /ŋ/)
Production of nasal sounds involves two major tubes that communicate with each other: pharyngeal-oral and nasal

Question 2

Why the Theory of Vowel Production Doesn’t Completely Cover Obstruents, Nasals, and Some Semivowels

Answer 2

Production of nasals, laterals, and obstruents includes coupled (shunt) resonators rather than single-tube resonators
Important acoustic energy is located below 4000 Hz for vowels and above 4000 Hz for obstruent sounds
Wavelengths for vowels are such that they plane waves propagate in the vocal tract and are easily related to the area function
Sound waves are more complex than planner and the area function does not completely describe the tube acoustics

Question 3

Why the Theory of Vowel Production Doesn’t Completely Cover Obstruents, Nasals, and Some Semivowels (Cont.)

Answer 3

Vowels have a complex periodic source (i.e., vocal fold vibration) located at one end of the single-tube resonator. Obstruents have aperiodic sources produced by air flowing through and against vocal tract structures

Question 4

Nasal murmur:

Answer 4

the interval during which the oral closure coincides with an open velopharyngeal port

Question 5

Shunt Resonators & Consonant Acoustics

Answer 5

English nasal phonemes (i.e., /m/, /n/, /ŋ/) are produced with oral airway closure and an open velopharyngeal port
Nasal murmur: the interval during which the oral closure coincides with an open velopharyngeal port
Distinguishes between acoustics of nasals produced with complete oral closure and nasalized vowels

Question 6

Nasal Murmurs figure

Answer 6

As in the case of vowels, the resonators shown in Figure 9–1 shape the spectrum of the source.
When shaping the source spectrum for vowels, there are frequency regions at which sound transmission through the vocal tract is maximum (i.e., resonances or formants).
For coupled (shunt) resonators, there are frequency regions where sound energy hits a kind of acoustic dead end, and is “trapped,” thus producing antiresonances.

Question 7

antiresonances

Answer 7

For coupled (shunt) resonators, there are frequency regions where sound energy hits a kind of acoustic dead end, and is “trapped,” thus producing antiresonances.

Question 8

Antiresonance ( what happens to the energy)

Answer 8

Energy may also be trapped in the smaller sinus resonators because the sinus cavities are closed resonators.
Regions of antiresonance can be calculated based on resonator type and size, just as in the vowel theory.
An antiresonance affects a measured spectrum in several ways, most notably by eliminating or reducing energy in its vicinity

Question 9

Nasal Resonances and Antiresonances

Answer 9

Theoretical spectrum for /m/ shows a sharply-tuned reverse peak around 800 Hz
Theoretical spectrum for /n/ shows a sharply-tuned reverse peak just below 2000 Hz
High amplitude of the first nasal resonance is greater than the amplitudes of higher-frequency nasal resonances
Typically of lesser amplitude compared with formant amplitudes of vowels preceding or following a nasal murmur

Question 10

Energy Loss in the Nasal Cavities

Answer 10

Nasal resonances tend to have wider bandwidths than resonances of a typical vowel spectrum
due to high absorption factors in the nasal cavities
More tissue to absorb sound in the nasal cavities than in the vocal tract
Results in damping of nasal resonances

Question 11

Energy Loss in the Nasal Cavities cont.

Answer 11

Antiresonances eliminate energy at the frequency of their “reversed peaks” and reduce energy at surrounding freqs
The overall amplitude of a sound can be thought of as the sum of all energy along the resonance curve. Therefore,
Speech sounds with antiresonances and increased damping have less overall amplitude than sounds that do not (i.e., vowels)

Question 12

Nasal Murmurs: Summary

Answer 12

Nasal murmur: the sound produced when the velopharyngeal port is open and there is a complete obstruction to the oral airstream.
Two major tubes are coupled: the nasal tube, which is open to the atmosphere, and the oral tube, which is completely sealed
The oral tube shapes the source spectrum, but the energy shaped by that tube is trapped because its outlet to the atmosphere is closed.
Results in an antiresonance, or a reverse peak in the spectrum.

Question 13

Nasal Murmurs: Summary
resonances

Answer 13

There are resonances of the nasal cavities, the most important of which is a low-frequency formant between 250 and 300 Hz.
This formant frequency is relatively constant for the three nasals of English, because the pharyngeal and nasal cavities responsible for the formant do not change shape across different places of articulation.

Question 14

Nasalization

Answer 14

Both pharyngeal-oral and nasal airways are open to the atmosphere
Output of the vocal tract for nasalized vowels represents a mixture of the resonant characteristics of both cavities and effects of their coupling

Question 15

Nasalization cont.

Answer 15

When nasal and pharyngeal-oral airways are coupled with both open to the atmosphere, sound waves propagate through both and radiate from the mouth and the nostrils
Nasal resonances are added into the spectrum for nasalized vowels
Antiresonances are also added into the spectrum

Question 16

Why Understanding Nasalization is Important

Answer 16

When English vowels are articulated either before or after nasals, some portion of the vowel is produced with an open velopharyngeal port.
Coarticulation
The open velopharyngeal port for the nasal murmur cannot be closed instantaneously for the articulation of a following vowel
a vowel preceding a nasal consonant is nasalized for a certain interval when the velopharyngeal port is opened prior to the oral articulation of the nasal murmur.

Question 17

Coarticulation

Answer 17

The open velopharyngeal port for the nasal murmur cannot be closed instantaneously for the articulation of a following vowel
a vowel preceding a nasal consonant is nasalized for a certain interval when the velopharyngeal port is opened prior to the oral articulation of the nasal murmur.

Question 18

Why Understanding Nasalization is Important cont.

Answer 18

Although English does not have a phonemic opposition for nasalized and non-nasalized vowels, such contrasts are phonemic in languages such as French and Hindi
Structural or neurological disorders that prevent the decoupling of the pharyngeal-oral and nasal cavities in speech production.
Craniofacial anomalies
Dysarthria

Question 19

Coupled (Shunt) Resonators in the Production of Lateral Sounds

Answer 19

Tongue raised allowing air to pass on either side of the midline of the vocal tract is referred to as a lateral manner of articulation–as with /l/ production
Cavity behind the apical closure,traps sound energy and introduces an antiresonance into the /l/ spectrum
The cavity behind the apical closure can be considered a shunt resonator

Question 20

Coupled (Shunt) Resonators in the Production of Obstruent Sounds

Answer 20

The production of obstruents involves a source of sound located between two resonating cavities.
For production of /ʃ/, there is a noise (aperiodic) source generated near the supraglottal constriction.
The /ʃ/ noise source has its spectrum shaped by the vocal tract.

Question 21

Coupled (Shunt) Resonators in the Production of Obstruent Sounds Cont.

Answer 21

The front and back cavities contribute to the vocal tract output because sound waves propagate away from the source in both directions (forward and backward)
Because the back cavity is effectively closed, it traps energy at frequencies determined by its size and generates an antiresonance.
The back cavity acts as a shunt resonator
These shunt resonators are seen in the production of fricatives, stops, and affricates