Nasal Stops
description
Transcript of Nasal Stops
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)