24.915/24.963�

Linguistic Phonetics

Source-filter analysis of fricatives�

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Figure removed due to copyright restrictions.

 

 

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Readings:�

• Johnson chapter 5 (speech perception)�

• 24.963: Fujimura et al (1978)�

 

 

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Noise source�

• Turbulence noise - random pressure fluctuations.�

• Turbulence can result when a jet of air flows out of a constriction into a wider channel (or open space).�

30

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00.5 1 2 3 5 10

Rel

ativ

e le

vel (

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Frequency (kHz)

Image by MIT OCW.Adapted from Stevens, K. N. "On the quantal nature of speech." Journal of Phonetics 17 (1989): 3-46.

 

 

 

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Noise source�

• Turbulence can result when a jet of air flows out of a constriction into a wider channel (or open space).�

• The intensity of turbulence noise depends on particle velocity.�

• For a given volume velocity, particle velocity will be greater if the channel is narrower, so for a given volume velocity, narrower constrictions yield louder frication noise.�

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00 0.1 0.2 0.3 0.4 0.5 0 0.1 0.2 0.3 0.4 0.5R

elat

ive

Lev

el (

dB)

source at glottis source at glottis

source at supraglottalconstriction

source atsupraglottalconstriction

Ag = 0.2 cm2 Ag = 0.3 cm2

Area of Supraglottal Constriction Ac (cm2)

Image by MIT OCW.Stevens, K. N. Acoustics Phonetics. Cambridge, MA: MIT Press, 1999.

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Noise source�

 • Turbulence is also produced when an airstream strikes an obstacle (e.g. the teeth in [s]).�

 • The orientation of the obstacle to the direction of flow affects the amount of turbulence produced - the teeth are more or less perpendicular to the airflow in [s] and thus produce significant turbulence.�

 • The louder noise of strident fricatives is a result of downstream obstacles. �

Image by MIT OCW.Stevens, K. N. Acoustic Phonetics. Cambridge, MA: MIT Press, 1999.

 

 

 

 

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Filter characteristics�

• The noise sources are filtered by the cavity in front of the constriction.�

• In [h] the noise source is at the glottis, so the entire supralaryngeal vocal tract filters the source, just as in a vowel.�

• So [h] has formants at the same frequency as a vowel with the same vocal tract shape, but the formants are excited by a noise source instead of voicing.�

• The noise source generated at the glottis has lower intensity at low frequencies, so F1 generally has low intensity in [h].�

Overallnoise source

Periodicsource

0 1 2 3 4 520

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SPL

in 3

00 -

Hz

Ban

ds(d

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002

dyne

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2 )

Image by MIT OCW.

 

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[h]�

• The noise source generated at the glottis has lower intensity at low frequencies, so F1 generally has low intensity in [h].�

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0

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0 1 2 3 4FREQ (kHz)

MA

G (d

B)

MA

G (d

B)

[he][e]

[o]

[h]

[h]

[ho]

Image by MIT OCW.

Image by MIT OCW.Stevens, K. N. Acoustic Phonetics. Cambridge, MA: MIT Press, 1999.

Overallnoise source

Periodicsource

0 1 2 3 4 520

30

40

50

60

70

Frequency (kHz)

SPL

in 3

00 -

Hz

Ban

ds(d

B re

0.0

002

dyne

/cm

2 )

�

[h]�

5000 5000

heed� hoed�

13.686 0

5000 Time (s) 14.1873

5000 17.5452

0

Time (s) 18.0608

Hoyd� hoard�

0 0 15.4067 15.9137 19.5239 20.0263

Time (s) Time (s)

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Filter characteristics�

 • As the place of articulation shifts forward, the cavity in frontof the noise source is progressively smaller.�

 • A smaller cavity has higher resonances, so other thingsbeing equal, the concentration of energy in the fricativespectrum is higher the closer the place of articulation is tothe lips.�

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01 2 3 4 6

5.9

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Freq

uenc

y (k

Hz)

sx

Image by MIT OCW. Image by MIT OCW.Adapted from Stevens, K.N. "On the quantal natureof speech." Journal of Phonetics 17 (1989): 3-46.

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Filter characteristics�

• The front cavity of a labial is so short (first resonance ~10kHz) that it has little effect on the fricative spectrum,resulting in fricative noise spread over a wide range offrequencies with a broad low-frequency peak.�

• This picture can be complicated by acoustic coupling withback cavity.�

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00 8000 12.0111 12.7989

Frequency (Hz) Time (s)

8000

0 0.641297 1.9567

Time (s)

si su

0

si –20

–40

0 8000 Frequency (Hz)

0

–20 su

–40

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Filter characteristics�

• Lip rounding lowers the resonant frequencies of the frontcavity, just as in vowels.�

00 2000 4000 6000 80008000 Frequency (Hz)

 

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Filter characteristics�

• In coronals, the presence or absence of a sublingual cavityhas a significant effect on the size of the front cavity.�

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dBkHz 2 4 6 8 10 kHz 2 4 6 8 10

S∫

Image by MIT OCW.

 

 

 

 

 

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Lip rounding/protrusion as an enhancement of sibilant contrasts�

• Postalveolar fricatives in English and French are produced with lip-rounding/protrusion (Ladefoged & Maddieson 1996:148), as areretroflex fricatives in Polish (Puppel et al 1977:157).�

• This realization can be analyzed as enhancing the perceptualdistinctiveness of the contrast with sibilants with smaller front cavities(e.g. anterior sibilants)�

•English, French: [s], Polish [s1, Ç]�

• [S] has larger front cavity than [s] - [S] has posterior constriction, sub-lingual cavity - and thus has lower spectral peaks. �

• Lip rounding further lowers the resonant frequencies of the front cavity,increasing this difference.�

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Image by MIT OCW.

ΚSource-filter analysis of stops�

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b d g40003000

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Image by MIT OCW.

 

 

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Stops�

• Stops are complicated in that they involve a series of rapidchanges in acoustic properties, but each component can beanalyzed in similar terms to vowels and fricatives.�

• A stop can consist of four phases: implosion (closure)transitions - closure - burst - release transitions�

0.129852Time (s)

0.4799590

5000

Components of a stop�

closure release transitions� closure� burst� transitions�

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0.494

0

–0.49720 0.231127

5000 Time (s)

0 0 0.231127

Time (s)

bal�

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Closure�

• Only source of sound is voicing, propagated through thewalls of the vocal tract.�

• The walls of the vocal tract resonate at low frequencies, somainly low-frequency sound is transmitted ('voice bar�). �

 

 

 

 

 

 

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Burst�

• Consists of a transient, due to abrupt increase in pressure atrelease, followed by a short period of frication as air flows athigh velocity through the narrow (but widening)constriction.�

• Transient source is an impulse (flat spectrum) filtered by thefront cavity.�

• The frication is essentially the same as a fricative made atthe same place of articulation.�

• Alveolars have high frequency, high intensity bursts.�

• Velar bursts are concentrated at the frequency of F2 and/orF3 at release.�

• Labial bursts are of low intensity, with energy over a widerange of freqeuncies, with a broad, low-frequency peak.�

 

 

 

 

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Release transitions�

• As the constriction becomes more open, frication ceases.�

• The source at this time is at the glottis - either voicing oraspiration noise. This source excites the entire vocal tract asin a vowel (or [h]).�

• The shape of the vocal tract, and thus the formants, duringthis phase are basically determined by the location of thestop constriction and the quality of adjacent vowels.�

• The formants move rapidly as the articulators move from theposition of the stop to the position for the vowel. Theformant movements are usually called 'formant transitions�.�

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Image by MIT OCW. Adapted from Ladefoged, Peter. Phonetic Data Analysis. Malden, MA: Blackwell, 2003.

 

 

 

 

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Release transitions�

• In alveolar stops the formant transitions due to release of thetongue tip constriction are probably very rapid (Manuel andStevens 1995), so the observed formant transitions appear tobe due to tongue body movements.�

• The tongue body is generally relatively front to facilitateplacement of the tongue tip//blade, thus there is a relativelyhigh F2 at release (~1800-2000 Hz) and high F3.�

• Labial stops involve a constriction at the lips. The tongueposition is determined by adjacent vowels, so the exactformant frequencies at release depend on these vowelqualities.�

• The labial constriction always lowers formants, so F2 andF3 are generally lower at release of a labial than in thefollowing vowel.�

 

 

 

 

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Release transitions�

• Velar stops involve a dorsal constriction, but the exactlocation of this constriction depends on the neighbouringvowels.�

• So the formant transitions of velars vary substantially,approximately tracking F2 of the adjacent vowel.�

• F2 and F3 are often said to converge at velar closure. Underwhat conditions should this occur?�

• Similar transitions are observed into and out of anyconsonant with a narrow constriction, e.g. fricatives, nasalstops.�

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Locus equations� • Typically F2 at the release of a consonant is a linear

function of F2 at the midpoint of the adjacent vowel(Lindblom 1963, Klatt 1987, etc).�

• The slope and intercept of this function depend on theconsonant.�

bid� bOd� 5000

0 0 1.96743 2.42708 11.3647 11.8142

Time (s) Time (s)

 

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Locus equations� • The slope and intercept of this function depend

on the consonant.�

Fowler (1994)�

2800260024002200200018001600140012001000

1000 1400 1800 2200 2600 3000

/b/ F

2 on

set (

Hz)

/b/ F2 vowel (Hz)

2800260024002200200018001600140012001000

1000 1400 1800 2200 2600 3000

/d/ F

2 on

set (

Hz)

/d/ F2 vowel (Hz)

2800260024002200200018001600140012001000

1000 1400 1800 2200 2600 3000

/b/ F

2 on

set (

Hz)

/g/ F2 vowel (Hz)

y = 1099.2 + 0.47767x R^2 = 0.954

y = 228.32 + 0.79963x R^2 = 0.968 y = 778.64 + 0.71259x R^2 = 0.930a. c.

b.

Image by MIT OCW.Adpated from Fowler, C. A. "Invariants, specifiers, cues: An investigation of locus equations asinformation for place of articulation." Perception and Psychophysics 55, no. 6 (1994): 597-610.

 

 

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Affricates�

• The frication portion of the release of the stop is prolongedto form a full-fledged fricative.�

• The fricative portion of an affricate is distinguished from aregular fricative by its shorter duration, and perhaps by therapid increase in intensity at its onset (short rise time).�

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24.915 / 24.963 Linguistic PhoneticsFall 2015

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