Nasal stops
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Nasal Stops. Nasals. Distinct vocal tract configuration. Nasal cavity (open). Oral cavity (closed). Pharyngeal cavity. Features of nasals. Vocal tract longer than for oral sounds ↓ resonant (formant) frequencies Nasal formant/murmur Nasal cavity is acoustically absorbent

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Nasal Stops

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Nasal Stops


Nasals

  • Distinct vocal tract configuration

Nasal cavity (open)

Oral cavity (closed)

Pharyngeal cavity


Features of nasals

  • Vocal tract longer than for oral sounds

    • ↓ resonant (formant) frequencies

    • Nasal formant/murmur

  • Nasal cavity is acoustically absorbent

    • Attenuates overall energy

    • Acts as a low-pass filter

  • Pharyngeal/oral cavity acts as a “cul-de-sac”

    • Introduces antiresonances/antiformants

  • Formant transitions

    • Varies for place of articulation


  • Bilabial /m/ Alveolar /n/ Velar / /


Formant Transitions

Bilabial

  • F1: very low

  • F2: ~ 600-800 Hz

    Alveolar

  • F1: very low

  • F2: ~ 1800 Hz

    Velar

  • F1: very low

  • F2:

    • Adjacent to back vowel ~ 1300 Hz

    • Adjacent to front vowel ~ 2300 Hz

  • F3:

    • near F2

    • F2-F3 transition is ‘wedge-shaped’


Oral Stops/Plosives


Aerodynamic Sequence

vowel plosive vowel

Intraoral Pressure Oral airflow Sound Pressure

time


Acoustic Sequence

voice onset time

release

burst

silent gap/

closure interval

vowel

vowel


What is it?

Period during VT occlusion

Voiceless:

relatively long

Voiced:

reduced or absent closure interval

May exhibit a “voice bar”

Silent gap/closure interval

voiceless

voiced

voice bar


Question

How can voicing continue with a closed vocal tract?


What is it?

Acoustic energy associated with VT release

Transient:

~10-30 msec

Aperiodic

Often absent in final position

Release burst


Release burst

  • Provides place information

  • Spectral shape related to cavity size in front of constriction

  • Bilabial:

    • diffuse energy dominant in low frequency

    • Either gently sloping spectrum or ~500-1500 Hz

  • Alveolar:

    • diffuse energy that is dominant in higher frequencies (>4000 Hz)

  • Velar:

    • compact energy in midrange (1500-4000 Hz)


Aspiration

  • Observed in voiceless stops

  • Consequence of air turbulence at the open glottis

  • Increases the duration of the release burst


Voiceless

Termed long lag VOT

VOT ranges from 25 – 100 msec

Voiced

Short lag:

Voice onset shortly after release

VOT>0

Simultaneous voicing:

voicing and release are coincident

VOT = 0

Prevoicing/VOT lead:

voicing occurs before release

VOT <0

VOT ranges from –20 – 20 msec

Voice onset time

voiceless

voiced


Voice onset time

  • VOT may distinguish place of articulation

  • Bilabial: relatively short VOT

  • Alveolar: mid-length VOT

  • Velar: relatively long VOT

  • RULE: as the cavity in front of the occlusion gets longer, VOT increases


(Azou et al., 2000)


Voice onset time has been considered an important measure of coordination. Why?


Formant Transitions

  • Formants of adjacent vowels will change with VT occlusion

  • Transitions will last about 50 msec (shorter than glides/liquids)

  • Transitions not obvious with voiceless

  • The form of the transition is a function of

    • The place of articulation

    • The neighboring sound

    • F1 and F2 are the key players


Formant transitions: bilabial

b

ah


Formant transitions: alveolar

d

ah


Formant transitions: velar

g

ah


Formant transition: voiced vs. voiceless

voiceless

voiced


VOT and clinical populations (Azou et al., 2000)

  • Aphasia

    • phonetic vs. phonemic errors

  • Apraxia & dysarthria

    • Marking, place, voicing and manner

    • Variability of productions


(Azou et al., 2000)


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