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
Intraoral Pressure Oral airflow
Sound Pressure
Aerodynamic Sequence
vowel
plosive
time
vowel
Acoustic Sequence
silent gap/
closure interval
vowel
release
burst
voice onset time
vowel
Silent gap/closure interval
voiceless
What is it?
• Period during VT occlusion
voiced
voice bar
Voiceless:
• relatively long
Voiced:
• reduced or absent closure
interval
• May exhibit a “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
Voiceless
• Termed long lag VOT
• VOT ranges from 25 – 100 msec
Voiced
• Short lag:
– Voice onset shortly after release
– VOT>0
voiced
•
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
•
•
•
•
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)