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 length of preceding vowel for final 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/