Stops
• Place– Bilabial /p/ /b/– Alveolar /t/ /d/– Velar /k/ /g/
• Voicing– Voiced /b/ /d/ /g/– Voiceless /p/ /t/ /k/
Stops: Articulatory manner
Sequence
1. Complete VT occlusion
2. Oral pressure positive– ~equal to subglottal P– 5-10 cm water
3. Rapid VT opening
4. Oral pressure=ambient
If VoicelessVocal folds abduct
Vocal folds adduct
Stops
• Occlusion and release results in two important feature of stops
• Acoustic silence, observed during build up of oral pressure
• Transient, aperiodic sound generated during the release of pressure
Stops: characteristic features
• Silent gap/closure interval
• Release burst
• Voice onset time
• Formant transitions
silent gap/closure interval
• Period during VT occlusion
• Often absent or reduced in voiced stops
• Voiced stops have voicing into and often throughout the closure interval
• How can voicing continue with a closed vocal tract?
Stops: characteristic features
• Silent gap/closure interval
• Release burst
• Voice onset time
• Formant transitions
Release burst
• transient (doesn’t last long)
• aperiodic (a wide range of frequencies, no harmonic structure)
• lasts 10-30 msec
• Often absent when stop is in the final position
Release burst
• Informative about place of articulation• Related to the size of cavity in front of
constriction• Bilabial: diffuse energy dominant in low
frequency (500-1500 Hz)• Alveolar: diffuse energy that is dominant in
higher frequencies (2500-4000 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
Stops: characteristic features
• Silent gap/closure interval
• Release burst
• Voice onset time (VOT)
• Formant transitions
Voice onset time
• Time between release and onset of phonation
• Considered to reflect laryngeal/articulatory coordination
• Is longer for voiceless than voiced stops
Voice onset time
• For voiced stops, VOT can be• Short lag: vocal folds vibrate shortly after
release• Simultaneous voicing: VOT = 0 since
voicing and release are coincident• Prevoicing VOT lead: VOT <0 since
voicing occurs before release• VOT ranges from –20 – 20 msec
Voice onset time
• Place of articulation is distinguished by VOT
• 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
Stops: characteristic features
• Silent gap/closure interval
• Release burst
• Voice onset time
• Formant transitions
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
• Place of articulation
• Bilabial– F1 starting value: close to 0 Hz– F2 starting value: ~ 600-800 Hz– F1 & F2 will usually rise toward the formants
of the adjacent sound
Formant Transitions
• Place of articulation
• Alveolar– F1 starting value: close to 0 Hz– F2 starting value: ~ 1800 Hz– F1 will always rise and F2 will go up or down
depending on the preceding and following vowels
Formant Transitions
• Place of articulation• Velar
– F1 starting value: close to 0 Hz– F2 starting value: ~ 1300 Hz when followed by a back vowel~ 2300 Hz when followed by a front vowel– F1 will always rise and F2 will go down– F3 is helpful with velars, typically the F2-F3 transition
is ‘wedge-shaped’ F2 going up, F3 going down
An important point…
• When discussing source-filter theory, the sound source was the glottal spectrum
• When discussing stops (and fricatives and affricates), we introduce a new sound source, noise produced within the oral cavity
• However, source-filter theory still holds even though the sound source is different…the vocal tract still filters the sound source, whether it is the complex periodic signal from vocal fold vibration, or a transient aperiodic signal produced during a stop release