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Stop/Plosives Stop/Plosives

Stop/Plosives - PowerPoint Presentation

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Stop/Plosives - PPT Presentation

Sound Source S tops fricatives and affricates produced in vocal tract as the sound source For voiced stops fricatives and affricates there are two sound sources P eriodic laryngeal source combined ID: 514627

voiced stops vot voiceless stops voiced voiceless vot vowel vowels closure release frequency energy burst locus front formant bilabials

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Presentation Transcript

Slide1

Stop/PlosivesSlide2

Sound Source

S

tops

, fricatives and affricates

produced in vocal

tract as the sound

source

For voiced

stops, fricatives and

affricates,

there are two sound

sources

P

eriodic

laryngeal source combined

with

A

periodic

vocal tract sound

source

Aperiodic

sound is produced by two different

manners:

Sudden release of air

pressure (burst/transient) behind closure

Stop/plosives

Turbulence

as air

rushes through a narrow

constriction

fricativesSlide3

Manner of Production

S

tops produced with -

complete closure

within the oral cavity,

build

up of pressure behind

the

closure and

rapid release

of

closure with air rapidly expelledSlide4

Acoustic Events

D

ivided

into five components

Occlusion

Transient

Frication

Aspiration

Transition

In practice, it is difficult to differentiate the transient from the frication, thus, this complex is generally referred to as the 

burst

.Slide5

Acoustic Events

occlusion

 is the period during which there is a stoppage of the airflow during which the pressure increases. It is

characterised

by silence or the absence of energy. Voiced stops may have low frequency (0 - 500Hz) periodic energy during this phase.

transient

 corresponds to the release of the closure. It is

characterised

by a spike on the spectrogram of intense energy with a duration of about 10msec.

frication

 component is the result of the combination of high intra-oral pressure being released through a narrow opening at the point of

release.

aspiration

 phase is the result of the vocal tract opening even further with turbulence through the glottis rather than the oral constriction. Formants are often present during this phase.

transition

 is the component where formants are present and the oral tract is moving to the position for the following vowel target.

In practice it is difficult to differentiate the transient from the frication so this complex is generally referred to as the 

burst

.Slide6

ACOUSTIC CUES TO THE VOICED/VOICELESS DISTINCTION

VOT

F1 of vowel following stop/plosive

Preceding vowel duration

Other cuesSlide7

1. Voice Onset Time (VOT)

Voiced and voiceless stops differ in the coordination between

supralaryngeal

and laryngeal events

Difference is referred to as differences in 

Voice Onset Time (VOT)

Voice onset time is the time that voicing begins relative to consonant release

In English, voiceless stops have large VOT values and voiced stops have small or negative VOT values.

Negative VOT occurs when periodicity begins before stop release i.e. during closure

English speakers hear a consonant as voiceless if VOT is over 25msec for bilabials, over 35

msec

for

alveolars

and over 40

msec

for velars

VOT values separating voiced from voiceless stops are language specificSlide8

1. Voice Onset Time (VOT)

Spanish

and French make use of

prevoiced

stops (negative VOT) and contrast these with positive VOT stops. English does not

recognise

a difference between

prevoiced

and voiceless

unaspirated

Thai speakers make a three way distinction for bilabials and

alveolars

. Voiced, voiceless

unaspirated

, voiceless

aspirated

Values also change in

context

VOT separation decreases for stops produced in sentences compared with initial stops produced in isolated

words

Stressed voiceless are produced with greater VOT values than

unstressed

VOT increases when stops occur in Stop Approximant sequences

VOT for

unaspirated

stops (/

sC

/ clusters) is close to VOT for voiced stops in CV

syllablesSlide9

2. F1 for Following Vowel

F1

provides important acoustic information

about

voicing

characteristics

F1 is very low during complete closure.

For voiced

stops--

F1

rises very quickly from

burst to

vowel target formant

position

R

ise steepest

in open vowels

(high F1),

and flattest in close vowels (low F1

)

For voiceless

stops

Periodicity (voicing)

occurs at least 30

msec

later than voiced stops so less of the formant will be pulse

excited

By

the time pulse excitation begins,

F1

has almost reached the vowel

target

On spectrograms, voiced stops

characterised

by a voiced, rising F1 transition which is

NOT present

in voiceless stops due

to

pulse

excitation begins later in the transition for voiceless

stops

aspiration requires open glottis

which (due to the large resonating sub laryngeal chamber) causes an attenuation of

F1

For VC

syllables—

F1

should fall sharply into the closure for voiced

stops

O

ffset frequency should

be higher for voiced than voiceless

stopsSlide10

3. Preceding Vowel Duration

Duration of vowels before voiceless stops is shorter than before voiced stops.

52-69% shorter vowel duration before voiceless than voiced

stops

Examples: Pop vs. BobSlide11

4. Other

Voiced stops have voicing/periodicity during closure when in intervocalic or postvocalic

position

Duration of

intervocalic closure provides an additional cue to

voicing

Closure

greater

for voiceless than voiced e.g. rapid

vs.

rabid

O

nset

frequency of

Fo

higher

following voiceless than voiced stops.

Burst intensity

of voiceless stops

greater

than

voiced stop.Slide12

CHARACTERISTICS OF ENGLISH STOPS IN

CONTEXTSlide13

Aspiration

When /

p,t,k

/

followed

by /

r,l,w,j

/

aspiration

manifests itself in the devoicing of the

approximants

"please", "try", "clean", "pew"

In final position and in unstressed syllables aspiration is

weak

When /s/ precedes /

p,t,k

/ initially , there is no

aspirationSlide14

Closure

/

b,d,g

/

only

fully voiced during closure

when occurring

intervocalicallySlide15

Release

Generally, stops have a release stage in the form of aspiration or as a following vowel. However, there are instances where the release does not

occur

No audible release in final position

: e.g. rope/robe

No audible release in stop clusters

: e.g. dropped, locked, good boy

Glottal reinforcement of final voiceless stops

:

Nasal

release

: If a stop is followed by a homorganic nasal in the following syllable, the release of air is usually via the nasal cavity. e.g. topmost, submerge, cotton, not now, red

nose

Lateral release:

 When the homorganic stops /

t,d

/ occur before /l/ they are released laterally. The tip remains in contact with the alveolar ridge but one or both of the sides is lowered allowing the air to escape. e.g. cattle, medal,

atlasSlide16

Place of Production

Place of articulation for stops

determined by

burst

transitionsSlide17

Burst

Burst

is

combination

of

transient

and frication

phase

Provide information

for place of

production

F

requency

spectrum

for

alveolars

and velars results from resonance

of

cavity in front of

tongue constriction

Alveolars

--front

cavity is small and place of

production

doesn't alter greatly

under influence

of different

vowels

V

elars

,

front

cavity shape varies greatly with different

vowels

Three

important parameters of

burst

that allow

one to differentiate

the place of

production

of stops:

Energy level

Spectral centre of gravity (frequency location

of

main energy concentration)

Spectral variance (whether the spectrum lacks peaks or has multiple peaks)Slide18

1. Energy Level

Alveolar stops have the most intense

bursts

B

ilabials

have

weakest bursts

Due to

lack of resonance for bilabials as no front cavity to amplify the

sound

Little

difference between

alveolar

and

velarSlide19

2. Center of Gravity

Bilabials lack any main resonance in the 0-10kHz range as there is no front cavity

so

characterised

by

gradually

falling distribution of energy

throughout

frequency

range

Alveolars

- broad distribution of energy in the burst

characterised

by prominence about 1.8 kHz and another rise between 2.5 -4.5

kHz

Velar - compact concentration of energy

in middle

of

spectrum

which varies according to F2 and F3 of

following vowel

F

requency

position of

energy

for velars derives from the cavity in front of

tongue constriction

Prevelar

(before front vowels (/kip/, /

gis

/), compact

energy

distributed around

center

frequency of about 3

kHz

Postvelar

(before back vowels(/

ko:t

/, /

go:d

/) compact energy

distributed

around

center

frequency of about 1

kHz

High

frequency bursts = alveolar 3kHz to 4kHz

Low

frequency bursts = bilabial 350Hz (but higher for front vowels)

Bursts

with energy slightly above the F2 for the following vowel = velar

e.g

back vowels = low F2 :700Hz, front vowels high F2:

3kHzSlide20

3. Formant Locus & Transitions

The 

locus theory

 proposes that the place of

articulatory

closure for each of the three places of articulation is relatively fixed regardless of following vowel and that this

articulatory

invariance has its acoustic correlate in the starting frequency of the second formant. Even though the formants may not reach the actual locus position they will still point to it.

Once we know the locus frequency we should be able to predict the slope of the second formant transition if we know the following vowel formant frequencies.

Therefore: The locus for /b/ is low (720Hz) and most vowels would have an F2 value greater than that then the transition will be rising in /

bV

/ syllables.

The locus for /d/ being at 1800Hz means that for central and back vowels F2 will fall in /

dV

/ syllables but will be level or slightly rising in /

di,dI,de

/.

Only the

alveolars

can be considered to have a relatively stable locus at around 1800 Hz. Cassidy and Harrington (1994) found that the variability in F2 onset frequency is least for /d/ followed by /b/ then /g

/.Slide21

3. Formant Locus & Transitions

F

or

bilabials and

velars,

there is not an invariant locus value as modifying

following

vowel will produce large changes in

formant

frequency

values

For instance, for bilabials F2 and F3 will have rising transitions before front vowels but F2 will be falling before

back

vowels

When F3 information is

included, better

picture of how the stops

cluster

F2/F3

plots show

tendency of

three clusters corresponding to bilabial, alveolar and

velar

However

there are examples of bilabials which are potentially confusable with velars preceding back

vowels

If we examine the change in F2 relative to the change in F3 (the difference between the formant value at onset and the value at the vowel target) then these bilabials are well

separated

C

annot

separate place of articulation on just one dimension such as F2 locus

.

Several

variables are required to give the whole

picture

L

ocus

is not invariant as

it changes

substantially as a result of

coarticulation