Part 2 Acoustics of Consonants

Question 1

Theory of Fricative Acoustics

Answer 1

Obstruents are produced with a noise source, usually located in the vicinity of the major constriction or at the point where an obstacle (e.g., the teeth) interrupts airflow within the vocal tract
⦁ Noise sources are aperiodic
⦁ In cases where the obstruent is voiced,
the voicing source occurs simultaneously with the vocal tract noise source
⦁ Mixed sources

Question 2

Laminar airflow

Answer 2

Laminar airflow within a tube. Laminar airflow is indicated by the parallel lines ending in arrowheads. Because pressure at the left of the tube (P1) is greater than pressure at the right of the tube (Pr), air flows from left to right, toward the lower pressure.

Question 3

Fluid Flow

Answer 3

As the air molecules enter the constriction they undergo an increase in speed.
⦁ They “shoot out” of the constriction exit in the form of a narrow stream or jet which expands as it moves downstream, toward the end of the tube.
⦁ The jet of air emerges from the constriction as a group of narrowly focused parallel lines.
⦁ There are also circular motions of air molecules along the edges of the jet.
⦁ turbulent flow, or turbulence.

Question 4

Fricative Production

Turbulence generated at the exit

Answer 4

Turbulence generated at the exit of the supralaryngeal (above the larynx and within the vocal tract) constrictions results in a frication source

Question 5

Source of sound in fricatives represents

Answer 5

Source of sound in fricatives represents a transformation of aeromechanical energy (in the form of turbulent flows) to acoustic energy (in the form of aperiodic waveforms and their spectra).
⦁ The tube model shows how air flowing through a constriction leads to the formation of a jet, around which turbulent flow is generated.
⦁ Air flows through a constriction because there
is a pressure differential across it. In fricative
production, pressure is higher in back of the
constriction than in front of it.

Question 6

Mixed Sources in Fricative Production
⦁ Production of the English fricatives /v/, /ð/, /z/, and /ʒ/ involves

Answer 6

Production of the English fricatives /v/, /ð/, /z/, and /ʒ/ involves turbulence, but may also be accompanied by vibration of the vocal folds
⦁ These voiced fricatives are produced with two types of sources
⦁ the aperiodic, turbulent flow generated in the vocal tract
⦁ The periodic vibration of the vocal folds
⦁ When there is a mixed source, both source spectra
are shaped by the resonant characteristics of the vocal tract

Question 7

Shaping of Fricative Sources by Vocal Tract Resonators

The narrow vocal tract constriction require

Answer 7

The narrow vocal tract constriction required for fricatives divides the vocal tract into a front and back cavity.

The source energy, located close to the constriction or in front of the constriction (e.g., at the teeth), is propagated in both directions along the long axis of the vocal tract
⦁ . Both the front and back cavities shape the source spectrum.

Question 8

Shaping of Fricative Sources by Vocal Tract Resonators cont.

The back cavity shapes

Answer 8

⦁ The front cavity, being open to the atmosphere, shapes the source spectrum by emphasizing a frequency region of the spectrum.
⦁ The emphasized frequencies appear in the output spectrum as high-amplitude regions, or broad peaks across a range of frequencies
The back cavity shapes the source spectrum by introducing antiresonances into the fricative output spectrum.

Question 9

Rule for Fricative Spectra

Answer 9

As the cavity in front of the constriction gets smaller, the resonances of the frication spectra move to higher frequencies.
⦁ This is consistent with the idea that air volumes in smaller resonating cavities are stiffer than air volumes in larger cavities.
⦁ As the cavity behind the constriction gets smaller, the resonant frequency of the antiresonances increases for the same reason.

Question 10

Measurement of Fricative Acoustics

Answer 10

⦁
The goal of a measurement strategy for fricative spectra is to obtain a set of numbers, that reliably distinguishes between fricatives having different places of articulation, and possibly even between fricatives having the same place of articulation but different voicing characteristics.
⦁
(no standard method, like F-patterns for vowels)

Question 11

Theory of Stop Acoustics

Answer 11

Airflow in a tube with a complete constriction in the tube (arrow) that prevents air from passing through to the right side.
⦁ Pressure builds up behind the constriction, as is the case for stop consonants. P1 is the pressure behind the constriction and Pr is the reference pressure (atmospheric pressure).

Question 12

Articulation of Stop Consonants

Answer 12

During speech production, completely closed tubes occur for the articulation of stop consonants.

The complete blockage of airflow for stops may be formed at several places throughout the vocal tract
⦁ In connected speech these complete blockages last no longer than about 100 ms (1/10 of a second)

Question 13

Articulation of Stop Consonants
Air molecules behind the stop construction

Answer 13

Air molecules behind the stop constriction are compressed simultaneously and uniformly

Nasal cavities are excluded from this volume because the velopharyngeal port is closed for production of stops (and all English obstruents)

Question 14

Air Compression for Voiced & Voiceless Stops

Answer 14

⦁
Air compression during voiceless stop ⦁ The peak (highest) value of Po is
equivalent to the peak values of Pt and Palv because the vocal folds are abducted
⦁ Air compression during voiced stop
⦁ Peak value of Po does not equal Pt and
Palv because as air flows through the
vibrating vocal folds there is some loss
of pressure.
⦁ Resulting in Po values that are generally

Question 15

Voiceless & Voiced Stops

Answer 15

A. (/t/) Oral, tracheal, and alveolar air pressures are equal during the stop closure interval.
⦁ B. (/d/) Air is compressed only in the spaces between the stop constriction and the larynx. Tracheal air pressure is greater than oral air pressure and both are greater than atmospheric air pressure

Question 16

Intervals of Stop Consonant Articulation: Aeromechanics and Acoustics

Answer 16

Closure (Silent) Interval
⦁ Vocal tract is sealed and radiates little or no acoustic
energy

Release (burst)
⦁ sudden drop of Po at the instant of stop closure release
creates an acoustic source of energy (shock excitation)

Frication Interval
⦁ When the constriction is released, the pressure
differential between Po and Patm generates turbulent airflow
⦁ Aspiration intervals (occurs only for voiceless
stops)
⦁ Turbulence is produced at the glottis due to narro

Question 17

Voice Onset Time

Answer 17

Voice Onset Time
⦁
Interval from stop burst to first glottal pulse of the following vowel
⦁ Burst Interval
⦁ Frication Interval
⦁ Aspiration Interval
⦁ VOT for voiceless stops is ~ 40-80 ms
⦁ VOT for voiced stops is generally less than
20 ms (voicing may precede stop burst)

Question 18

Shaping of Stop Sources by Vocal Tract Resonators

Answer 18

⦁
As in vowels and fricatives, the acoustic output of the vocal tract for stops is the result of source spectra shaped by vocal tract resonators
⦁ stops are produced with a succession of changing sources

Question 19

The Nature of Stop Sources
⦁
Silent interval of a voiceless stop has no

Answer 19

⦁
Silent interval of a voiceless stop has no source, whereas the silent interval of a voiced stop has a vocal fold vibration source
⦁ Voiced source is not shaped by a vocal tract filter in the same way as vowels or nasals because the tract is closed
⦁ Vibration of the vocal tract walls and tissues of the neck, which only pass very low frequencies

Question 20

Nature of Stop Sources Cont.
⦁
The burst gives way to turbulent noise

Answer 20

The burst gives way to turbulent noise sources: frication and aspiration for voiceless stops or only frication in voiced stops.
⦁ Shock excitation is an impulse-like event, or one that is characterized by a large change in amplitude over a very brief
interval.
⦁ Spread acoustic energy across a wide range of
frequencies, producing a spectrum with roughly
equal energy at all frequencies.
⦁ The source spectrum of shock excitation is

Question 21

Shaping of Stop Sources
⦁ Shock excitation and frication sources are

Answer 21

⦁ Shock excitation and frication sources are typically located within the vocal tract, between two resonators.
⦁ The cavity in front of the stop source provides the primary emphasis of energy (resonance) in the output spectrum, and the cavity behind the source contributes one or more antiresonances to the output spectrum.
⦁ The general spectral shapes of stop bursts are related to articulatory configurations

Question 22

Measurement of Stop Acoustics
⦁
Goal of a measurement strategy for

Answer 22

Goal of a measurement strategy for stop burst spectra is to obtain a small set of numbers that distinguishes among the three places of articulation.
⦁ Temporal segmentation of closure intervals and VOT for stop consonant waveforms is relatively straightforward

Question 23

Stop Consonants: Summary
⦁ Stops are produced when there is

Answer 23

⦁ Stops are produced when there is a constriction in the vocal tract that completely blocks the airstream for a brief interval.
⦁ During the closure interval the pressure behind the constriction (Po) builds up and is suddenly released when the articulators break the constriction.
⦁ The sudden drop in pressure serves as an acoustic source called shock excitation, the spectrum of which is shaped by the vocal tract cavities.

Question 24

Stop Consonants: Summary Cont.
⦁ The cavity in front of the stop constriction

Answer 24

⦁ The cavity in front of the stop constriction provides the major resonance that shapes the shock excitation source
⦁ The cavity in back of the constriction contributes antiresonances to the output spectrum
⦁ Sequence of acoustic events associated with stops: closure interval, burst, frication interval, and aspiration interval (only for voiceless stops).
⦁ Spectra of the burst and frication intervals are
unique for each of the three stop places of

Question 25

Theory of Affricate Acoustics

Answer 25

Affricates combine features of stop consonants and fricatives.
⦁ Affricates have a closure interval during
which Po rises and is released when the articulatory constriction is broken
⦁ results in a burst similar to a stop burst
⦁ Affricates distinguished from stops by the long interval of the frication noise
⦁ 60-80 ms compared to 30-50 ms for stops

Question 26

Affricate Acoustics Cont.
⦁
Frication noise occurs when the conditions

Answer 26

Frication noise occurs when the conditions for turbulent airflow exist:
⦁ (a) a flow of sufficient magnitude
⦁ (b) a sufficiently narrow constriction Affricates have been described as “slowly
released stops”
Affricates of American English, (/tʃ/ and /dʒ/) may also have a place of articulation that is slightly posterior from the lingua-alveolar place of /t/ and /d/

Question 27

Acoustic Contrasts Associated with the Voicing Distinction in Obstruent

VOTs of voiceless stops are

Answer 27

⦁
VOTs of voiceless stops are typically longer
than those of voiced stops
⦁ Typically between 0 and 20 ms for voiced stops
and 40 and 80 ms for voiceless stops.
A VOT of zero means that glottal pulsing begins at the same time as the release of the stop (i.e., the burst).
Short VOTs of voiced stops are due to the absence of the aspiration interval, as well as shorter burst and frication intervals

Question 28

Review
⦁ A theory of consonants is similar in some

Answer 28

A theory of consonants is similar in some respects to the theory of vowel acoustics, but also differs from the latter in important ways.
⦁ Antiresonances occur when two resonators are coupled, as in the case of nasals and laterals, or when a source sits in-between two vocal tract resonators, as in the case of stops, fricatives, and affricates.
⦁ Nasal murmur and nasalization spectra include antiresonances as well as resonances

Question 29

Review cont.
⦁ Lateral /l/ has an antiresonance originating

Answer 29

Lateral /l/ has an antiresonance originating in the closed cavity between the tongue tip contact with the alveolar ridge and the tongue dorsum contact (or near contact) with the soft palate
⦁ The primary resonator in obstruent production is determined by the size of the resonator in front of the constriction.
⦁ Turbulent airflow is generated when a sufficiently high airflow is forced through a sufficiently narrow constriction.

Question 30

Review cont.
⦁ Stop consonants have a shock excitation

Answer 30

Stop consonants have a shock excitation source, which is the acoustic result of sudden release of the positive oral pressure developed during the silent interval.
⦁ VOT is the duration between a stop consonant burst and the first glottal pulse of a following vowel
⦁ Affricates are best understood as slowly released stop consonants