Transcript Acoustic Characteris..

Acoustic Characteristics of
Consonants
Robert A. Prosek, Ph.D.
CSD 301
Consonants
• Consonant articulations are more complex than vowel
articulations
• consonants are usually described in groups according
to their significant acoustic and articulatory properties
• stops
• fricatives
• affricates
• nasals
• glides
• liquids
Stop Consonants (1)
• Stop consonants are characterized by a complete
closure somewhere in the vocal tract
• Three phases
• closure
• release
• transition
• reverse the steps for postvocalic stops
Stop Consonants (2)
• Stop gap
• this event corresponds to the complete closure of the
vocal tract
• minimum radiated acoustic energy
• silence for voiceless stops
• voice bar for voiced stops
• 50 - 150 ms
Stop Consonants (3)
• Stop release (burst)
• pressure has been rising behind the obstruction
• rapid release produces a transient
• 20 - 30 ms
• thus, suitable temporal resolution is needed
• voiceless stops follow the burst with frication
• noise generated at the place of articulation
• low frequency for /p/ (500 - 1500 Hz) (falling spectrum)
• high frequency for /t/ (above 4 kHz) (rising spectrum)
• mid-frequency for /k/ (1.5 - 4 kHz) (peaked spectrum)
Stop Consonants (4)
• Cues for voicing
• /p t k/ are phonetically distinguished from /b d g/ by
voicing
• VOT is the interval between the release of the stop
and the onset of vocal fold vibration
• for /b d g/ VOT from -20 to +20 ms with a mean of
10 ms
• for /p t k/ VOT from 25 to 80 ms with a mean of 45
ms
• voice bar for intervocalic stops
Stop Consonants (5)
• Formant transitions
• articulatory movement from stop to vowel entails a
formant movement
• as the resonating chamber of the vocal tract changes,
the formant frequencies change
• formant transitions are important for perception
• formant transitions are approximately 50 ms in
duration
Stop Consonants (6)
• Formant transitions (continued)
• F1 usually rises for the stop consonants
• F2 and F3 are not so simple
• for /p b/ F2 and F3 rise slightly
• for /t d/ F2 falls and F3 rises slightly
• for /k g/ F2 and F3 separate steeply and rapidly
• However, a given stop is associated with a variety of
transitions (see Fig. 5-14)
• there is no fixed transition pattern for perception
• Cue trading in stop consonants
Fricatives
• Articulation
• Narrow constriction in the vocal tract
• When air flow rate is high, turbulence results
• Turbulence is complex, unpredictable air flow
• Turbulent airflow is perceived as turbulent noise
• Fricatives have a relatively long duration
• Fricatives are divided into
• sibilants (stridents)
• nonsibilants (nonstridents)
Fricatives (2)
•
Sibilants
•
Intense noise
•
Differentiated among themselves by
•
•
•
•
voicing
•
noise spectrum
Voicing
•
pulses (glottal closures) for /z ʒ/
•
no pulses for /s ʃ/
Noise spectrum
•
Alveolar sibilants have higher frequency energy
•
Palatal sibilants have energy down to 3 kHz
•
Spectral irregularities aren’t important in perception
Formant transitions
•
Formant transition locations depend on the articulation, but the transitions are not important perceptually for sibilants
•
Fricatives (3)
Nonsibilants /f v θ ð h/
•
Less noise energy than sibilants
•
Voiced nonsibilants will have quasi-periodic pulses
•
Noise spectra are
•
fairly flat
•
diffuse
•
The relationship between noise spectrum nonsibilant
identification is not known
•
Formant transitions play the primary role in perception
•
Noise spectrum may play a secondary role
Fricatives (4)
• Acoustical needs for fricatives
• Measures that are economical
• Economical
• Valid
• Reliable
• Problems
• Ambient noise
• Filtering values
Affricates
• Described as a combination of stop and fricative
• /ʧ ʤ/
• Articulation
• complete obstruction in the vocal tract
• intraoral pressure builds up
• release to generate fricative noise
• Acoustic features
• rise time
• duration of frication
• relative amplitude in third formant region
• stop gap
Nasals
•
•
Articulation
•
complete closure in vocal tract
•
sound radiated through nasal cavities
•
sometimes called nasal stops
•
/m n ŋ/
Acoustics
•
Nasal murmur - sound of a nasal
•
associated strictly with nasal radiation of sound
•
there are many spectral peaks, but most have low amplitude
•
antiformants
•
nasal formant
•
low frequency (~300 Hz)
•
highest energy
Nasals (2)
• Nasal formant (continued)
• consonant energy, overall, is reduced because
• higher formants have reduced energy
• Other acoustic features
• highly damped formants (broad bandwidths)
• formant transitions in connected speech
Glide Consonants
• Also called approximants and semivowels
• /w ʲ/
• Articulation
• gradual articulatory motion
• narrow, but not closed, vocal tract
• Acoustics
• Formants
• for /w/
• F1 and F2 are both low
• for /ʲ/
• low F1 and high F2
Liquid Consonants
• Also included as semivowels
• /ɹ l/
• Characterized by
• rapid movements
• formant structure
• F3 is the main difference
• Antiformants for /l/