Acoustic Characteristics of Consonants

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 • 50 - 150 ms

6. 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)

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/