24.963�

Linguistic Phonetics�The acoustics of nasals and

laterals

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Image by MIT OCW. Adapted from Stevens, K. N. Acoustic Phonetics.

Cambridge, MA: MIT Press, 1999, chapter 6.

 Assignments • Talk to me about a paper topic, this week or next.

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Damping and bandwidth

• When an input of energy sets a body vibrating, the resulting vibrations die out as energy is dissipated through friction, transmission of energy to surrounding air, etc.

• A wave of this type is described as damped.

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Image by MIT OCW.Adapted from Ladefoged, Peter. Elements of Acoustic Phonetics.Chicago, IL: Univeristy of Chicago Press, 1962.

 

 

Damping and bandwidth

• The more heavily damped a sinusoid is, the wider the bandwidth of its spectrum.

• A wider bandwidth implies a lower spectral peak, other things being equal, since the energy in the wave is distributed over a wider range of frequencies.

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Air

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Various waves and their spectra.004 .005.003

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a b c d e

Image by MIT OCW. Adapted from Ladefoged, Peter. Elements of Acoustic Image by MIT OCW.

Phonetics. Chicago, IL: Univeristy of Chicago Press, 1962. Adapted from Ladefoged, Peter. Elements of Acoustic Phonetics. Chicago, IL: Univeristy of Chicago Press, 1962.

 

 

 

Damping and bandwidth

• Standing waves in the vocal tract are damped due to friction, radiation losses to the outside air, absorption of energy by the elastic vocal tract walls etc.

• Greater surface area results in more damping (and broader formant bandwidths).

• Coupling the nasal cavity to the vocal tract in in nasal sounds increases the surface area of the vocal tract.

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Nasal stops

• A uvular nasal can be modeled in terms of a tube which is closed at the glottis and open at the nostrils.

• It is not a uniform tube. • The effective length of the tube is greater than the length

from glottis to lips – 21.5 cm (Johnson) or 20 cm (Stevens) vs. 16 cm.

• So the resonances of the tube are at lower frequencies (and closer together) than in a vowel.

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Nasal stops

• In nasal consonants formed with an oral constriction further forward than the uvula, the oral cavity forms a side branch on the pharyngeal-nasal tube.

• This side branch is longest in labials, shortest in velars.

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(A) (B)

(m)

Nose

Mouth

Pharynx

(A) An X-ray tracing of the positions of the articulators during (m).(B) A tube model of this vocal tract configuration.

Image by MIT OCW.Adapted from Johnson, Keith. Acoustic and AuditoryPhonetics. Malden, MA: Blackwell Publishers, 1997.

 

 

 

 

Nasal stops • The side branch is a tube open at one end and resonates

accordingly. • The side branch is not coupled to the outside air. Its

resonances are zeros in the signal radiated from the nose -i.e. those frequencies are attenuated.

• Zeroes also reduce the amplitude of higher frequencies, so nasals are characterized by less high frequency energy than vowels.

• Frequencies of the zeroes depend on the size of the side branch, e.g. 8 cm for [m], 5.5 cm for [n].

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Nose

Mouth

Pharynx

A tube model of this vocal tract configuration.Image by MIT OCW.

Adapted from Johnson, Keith. Acoustic and AuditoryPhonetics. Malden, MA: Blackwell Publishers, 1997.

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Nasal stops

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Fre

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Fre

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0 0 0.03722 0.2246 9.767 9.988

Time (s) Time (s)

[m] my[n] nigh

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Cues to place in nasal stops

• Formant transitions – as in oral stops• Nasal murmur differs according to place of articulation,

but in itself is a weak cue – murmur is relatively quiet.• But the interval around the release of the nasal may

provide significant place cues:– Nasal place is identified more accurately from 6

periods centered around release compared to 6 periodsof the murmur or formant transitions (Kurowski &Blumstein 1984)

– But the differences are small: 12% vs. 13% vs. 20%• The interval around the onset of nasal closure does not

provide comparable cues to place (Repp & Svastikula 1988)

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Laterals

• Laterals also have a side branch - the pocket behind thetongue tip is a side branch to the main tube(s) passingaround the side(s) of the tongue.

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(a)

[l]

13.5 cm

2.5 cm

2.5 cm40 cm3

A = 0.17 cm2

l = 1.0 cm

Image by MIT OCW.

Image by MIT OCW.Adapted from Johnson, Keith. Acoustic and Auditory Phonetics Malden, MA: Blackwell Publishers, 1997.

 

 

 

 

Laterals

• Laterals also have a side branch - the pocket behind the tongue tip is a side branch to the main tube(s) passing around the side(s) of the tongue.

• Laterals are thus also characterized by zeroes - the lowest appears between F2 and F3, often significantly reducing the amplitude of F2.

• The presence of zeroes and the coronal constriction reduce the intensity of laterals compared to most vowels.

• On spectrograms, laterals look similar to nasals, but differ in the location of formants and zeros, and in their effects on neighboring vowels.

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Laterals

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[n] nigh [l] lie

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Laterals

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[dli(ma)] (Hebrew)

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Nasalized vowels

• Nasalized vowels involve a complex vocal tractconfiguration.

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Nose

Mouth

Pharynx

Image by MIT OCW.Adapted from Johnson, Keith. Acoustic and AuditoryPhonetics. Malden, MA: Blackwell Publishers, 1997.

 

 

Nasalized vowels

• The coupled nasal cavity contributes both formants andanti-formants (poles and zeroes) which combine with theformants of the oral tract.

• The net acoustic effect of velum lowering depends on thelocations of the formants in the corresponding oral vowel(Maeda 1993)

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Nasalized vowels

Z2M

agni

tude

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OralNasal (NC = 1.6)

i

ε

ο

u

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'

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''

Image by MIT OCW.Adapted from Maeda, Shinji. "Acoustics of vowel nasalization and articulatory shifts in French nasal vowels."In Nasals,Nasalization and the Velum. Edited by M. Huffman and R. Krakow. New York, NY: Academic Press, 2003, pp. 147-170.

 

 

 

Nasalized vowels

• As a result it is difficult to give a general acousticcharacterization of nasalization on vowels.

• Maeda: nasalized vowels generally have a flat, lowintensity spectrum in the low frequency region.

– Addition of the lowest nasal formant in combinationwith broad bandwidth F1 can create a broad, lowfrequency prominence.

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'Don's bed''dot bend'

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

 

   

Nasalized vowels

• Chen (1997) proposes the measures A1-P0 and A1-P1 toquantify nasalization.

– A1 is amplitude of F1– P0 is amplitude of the low frequency nasal peak.– P1 is amplitude of a higher nasal peak, between F1 and F2.

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• A1 amplitude of F1• P0 amplitude of lower frequency

nasal peak - intensity of harmonicwith greatest amplitude at lowfrequency.

• P1 amplitude of nasal peak -measured as amplitude of highestharmonic near to 950 Hz.

• These measures are sensitive tovowel quality - Chen proposescorrections to adjust for this.

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Image by MIT OCW.Adapted from Chen, Marilyn Y. "Acoustic correlates ofEnglish and French nasalized vowels." The Journal ofthe Acoustical Society of America 102 (1997): 2360.

 

Nasalized vowels

• Perceptually, nasal vowels are less distinct from eachother than oral vowels, both in terms of confusability(Bond 1975) and similarity judgements (Wright 1986).

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Dimension II

The first two dimensions in theperceptual space as determined byINDSCAL

F1 versus F2 plot of the mel values ofthe stimuli

F2 in mels

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Image by MIT OCW.Adapted from.Wright, James T. "The behavior of nasalized vowels in the perceptual vowel space." In ExperimentalPhonology. Edited by J. J. Ohala and J. J. Jaeger. Orlando, FL: Academic Press, 1986, 45-67.

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Nasalized vowels

• More specifically, high nasalized vowels are perceived aslower than their oral counterparts and low nasalizedvowels are perceived as higher than their oralcounterparts.

• Wright speculates that this may be related to the fact thatFN1 is below F1 in low vowels and above it in high andmid vowels in his stimuli.

 

Nasalized vowels

• This greater confusability is reflected in the fact that, inlanguages with contrastive vowel nasalization, the nasalvowel inventory is always the same as or smaller than theoral vowel inventory, never larger (Ferguson 1963, Ruhlen1973).

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Beembe (Congo) Dakota (Yankton-Teton)

~ ~ ~ ~i u i u i u i u~ ~e o e o e o

~a a ~a a

Portuguese (Continental) Ebrie (Niger-Congo)

~ ~i u i u i u~ ~e o e o ~ ~e o e o

ε c

~a a~a a

Image by MIT OCW.

   

 

  

pin-pen neutralization

• Southern US (and Bakersfield) accents:– pin-pen, him-hem are homophonous, pit-pet contrast.

• Vowels are substantially nasalized before nasals in English.• Nasalization reduces the distinctiveness of F1 contrasts• Oral [I]-[E] are sufficiently distinct, nasalized [I) ] are]-[E)

not.

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Phonological map of the US removed due to copyright restrictions.Source: http://www.ling.upenn.edu/phono_atlas/home.html.

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