1. Acoustic Characteristics of Consonants
Robert A. Prosek, Ph.D.
CSD 301

2. 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

3. 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

4. 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 ms

6. Stop Consonants (3) Stop release (burst)
pressure has been rising behind the obstruction
rapid release produces a transient 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/ ( Hz) (falling spectrum)
high frequency for /t/ (above 4 kHz) (rising spectrum)
mid-frequency for /k/ ( kHz) (peaked spectrum)

8. 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
length of preceding vowel for final stops

11. 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

12. 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

13. 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)

14. 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

18. 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

21. Fricatives (4) Acoustical needs for fricatives
Measures that are economical
Economical
Valid
Reliable
Problems
Ambient noise
Filtering values

22. 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

23. 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

24. 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

26. 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

27. Liquid Consonants Also included as semivowels /ɹ l/ Characterized by
rapid movements
formant structure
F3 is the main difference
Antiformants for /l/