Nasal Stops. Nasals Distinct vocal tract configuration Pharyngeal cavity Oral cavity (closed) Nasal...

Nasal Stops

Nasals

• Distinct vocal tract configuration

Pharyngeal cavity

Oral cavity (closed)

Nasal cavity (open)

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 TransitionsBilabial• 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

time

vowel plosive vowel

Intr

aora

l Pre

ssur

e O

ral a

irflow

Soun

d Pr

essu

re

Acoustic Sequence

vowel vowel

releaseburst

silent gap/closure interval

voice onset time

Silent gap/closure interval

What is it?• Period during VT occlusion

Voiceless: • relatively long

Voiced:• reduced or absent closure

interval• May exhibit a “voice bar”

voiceless

voiced voice bar

Question

How can voicing continue with a closed vocal tract?

Release burst

• What is it?• Acoustic energy associated with VT release

• Transient: – ~10-30 msec

• Aperiodic • Often absent in final position

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

Voice onset time

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

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

ahb

Formant transitions: alveolar

ahd

Formant transitions: velar

ahg

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)