Speech Science Fall 2009 Oct 28, 2009

Outline Acoustical characteristics of Nasal Speech Sounds Stop Consonants Fricatives Affricates

Acoustics of the Nasals The addition of nasal cavity creates vocal tract a longer and larger resonator. Therefore, it naturally responds to lower frequencies. Acoustic result is called “murmur” This murmur or formant lies within the Hz range Acoustically, nasal consonants are weak due to antiresonances within the vocal tract.

Acoustics of the Nasals The antiresonances are frequency regions in which the amplitudes of the source components are severely attenuated. Consonants are articulated with more constriction or occlusions than vowels. Resonances and antiresonances can cancel each other if those frequencies are close enough or one formant may appear as two. The elongated vocal tract also causes weak nasal consonants. Antiresonances can also attributed to soft walls of nasal cavity

Acoustics of the Nasals The frequency ranges for the antiresonances associated with nasal sounds vary with place of articulation. For /m/, antiresonance is in the range of Hz. For /n/, the range is between Hz and for / /, it is above 3000 Hz.

Nonresonant Consonants: Stops Stop consonants Voiceless: /p/, /t// and /k/ Voiced: /b/, /d/, and /g/ These sounds are articulated with the greatest degree of obstruction to the breath stream

Stops: Acoustic features 1) Silent gap It is the hold period in articulation (no flow of air out of the vocal tract)

Stops: Acoustic features 2) Noise burst It is at the moment of release It appears as a vertical line in spectrograms Noise bursts are very brief (i.e., ms) and covers broad range of frequencies with varying intensity Most intense frequency depends upon the place of articulation

Stops: Acoustic features 3) Rise and fall time The speed with which the acoustic signal attains maximum intensity (syllable initial stops) or falls to minimum intensity (for syllable final stops) Rise and fall times are both very rapid for stop consonants

Stops: Acoustic features 4) Change in F1 The first formant rises rapidly after the release of initial stops It falls rapidly before the completion of the closure for the final stops. (review: first formant frequency is positively correlated with the size of mouth opening). This rise and fall depend upon the neighboring vowels.

Stops: Acoustic features Stops: Place of articulation A) Most intense frequency of the transient burst varies with place of articulation. /p/ and /b/ generally have maximum intensity around 600 Hz and below. /t/ and /d/ have most intensity in high frequency area around 3000 Hz.

Stops: Acoustic features Stops: Place of articulation /k/ and /g/ present a variable picture. Spectral peaks of bursts are associated F2 of the following vowel after stop. Intense portion of burst extends upward from the f2 of the following vowel.

Stops: Acoustic features Stops: Place of articulation B) Formant transition Right after occlusion is released, the rapid movements of the articulators cause sudden change in resonance peaks of vowel tract. They occur during transition from one speech sound to another They are called formant transitions.

Stops: Acoustic features Stops: Place of articulation B) F2 transition (review: F2 was correlated with the length of the front cavity) For stops, F2 varies with the neighboring vowel. Direction of frequency change in F2 changes with vowel preceding or following a stop.

Formant transitions tics/acoustic/img/formant-transitions.png

Stops: Acoustic features Stops: Voiced and voiceless During intervocalic contexts, for /b/, /d/, and /g/, phonation continues through out the period of articulatory closure. For /p/, /t/, /k/, phonation ceases during closure. During prevocalic contexts, we do not normally phonate during the closure of above sounds.

Stops: Acoustic features Stops: Voice onset time (VOT) For /b/, /d/, and /g/, phonation begins at or very shortly after stop release. For /p/, /t/, and /k/, there is a delay of at least 50 ms before phonation begins after the release. This relative timing of stop release and the initiation of phonation has been called voice onset time (VOT). Lisker and Abramson

Stops: Acoustic features VOT : it is measured in milliseconds as the duration between the onset of transient burst of stop release and the first vocal pulse. If onset of phonation follows stop release, VOT values are positive. If voicing onset precedes stop release, VOT values are negative.

Stops: Acoustic features Stops: Aspiration It is a period of voicelessness after stop release. It is associated only with /p/, /t/, and /k/. Open glottis at the moment of stop release allows the breath stream to flow freely into the upper vocal tract without generating phonation. The reverse is true for voiced stops.

Fricatives English fricatives have five articulatory positions: labio-dental: f,v - fine, vine dental: þ,ð - think, this alveolar: s,z - price, prize post-alveolar:, - mission, vision glottal: h - hard

Fricatives The fricative noise originates at the articulatory constriction. Spectrum at the lips is determined by the resonant characteristics of the constriction and portion of the vocal tract anterior to the noise source.

Fricatives For /v/, and /f/, fricative energy is very low in intensity because there is no appreciable resonating cavity anterior to the point of constriction. But frequency band is broad. /s/ and /z/ have a very narrow band of frequency and high energy noise. For /s/, most of the energy is above 4000 Hz. For [ ʃ ], it energy is around 2000 Hz because point of articulation is farther back in the mouth, thus resonating cavity anterior to that is longer. This results in lower frequencies for [ ʃ ] than /s/.

Affricates Acoustically, these sounds present combination of stop and fricative features Stop closure Bust noise (release of stop) Extended duration of aperiodic sound (friction)