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Nasal Stops

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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  1. Nasal Stops

  2. Nasals • Distinct vocal tract configuration Nasal cavity (open) Oral cavity (closed) Pharyngeal cavity

  3. 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

  4. Bilabial /m/ Alveolar /n/ Velar / /

  5. 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’

  6. Clinical Diversion • Measuring velopharyngeal function • Visualization: nasendoscopy • Aerodynamic: oral-nasal airflow • Acoustic: Nasometry

  7. Two microphones Oral Nasal Separated by solid plate Nasalence: Nasal/oral energy Application Variety of “nasal resonance” disorders Nasometer

  8. Example from Literature Childhood apraxia Repaired cleft Typically developing From Skinder-Meredith, Carkoski, Graf (2004)

  9. Oral Stops/Plosives

  10. Aerodynamic Sequence vowel plosive vowel Intraoral Pressure Oral airflow Sound Pressure time

  11. Acoustic Sequence voice onset time release burst silent gap/ closure interval vowel vowel

  12. 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 voice bar voiced

  13. Question How can voicing continue with a closed vocal tract?

  14. What is it? Acoustic energy associated with VT release Transient: ~10-30 msec Aperiodic Often absent in final position Release burst

  15. 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)

  16. Aspiration • Observed in voiceless stops • Consequence of air turbulence at the open glottis • Increases the duration of the release burst

  17. 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

  18. 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

  19. (Azou et al., 2000)

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

  21. 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

  22. Formant transitions: bilabial b ah

  23. Formant transitions: alveolar d ah

  24. Formant transitions: velar g ah

  25. Formant transition: voiced vs. voiceless voiceless voiced

  26. VOT and clinical populations (Azou et al., 2000) • Aphasia • phonetic vs. phonemic errors • Apraxia & dysarthria • Marking, place, voicing and manner • Variability of productions

  27. (Azou et al., 2000)

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