Voice Onset Time+ Voice Quality November 28, 2011
The Future • Production Exercise #3 is due. • This week: the basics of obstruent acoustics • On Wednesday: cues for place of articulation. • On Friday: more spectrogram matching. • Next week: sonorant acoustics • approximants and nasals • Production Exercise #4 for Wednesday the 7th.
Review: Stops and Voicing • Stops • Three stages: close, maintain, release • Pressure build-up behind closure • “Release Burst” • Voicing • Vocal folds are lightly brought together (adducted) • Sub-glottal pressure higher than supra-glottal pressure • Airflow through glottis causes cycle of vocal fold opening and closing • Voiceless: k > t > p Voiced: b > d > g
It’s not that simple • The voicing of stops is difficult, so the contrast between voiced and voiceless stops often takes a different form • Making use of a different property: aspiration • An aspirated stop has the following timing: • Stop closure is made • Airflow builds up pressure behind closure • Closure is released (with a “burst”) • Air flows unimpeded through glottis (“aspiration”) • Vocal folds close; voicing begins
An Aspirated Stop: [phœt] aspiration release burst [t] release burst voicing (vowel) [t] closure
An Unaspirated Stop: [pœt] voicing (vowel) release burst
A Voiced Stop: [byt] release burst voicing (closure) voicing (vowel)
Voice Onset Time • Voice Onset Time (VOT) is defined as the length of time between the release of a stop closure and the onset of voicing. • For aspirated stops--voicing begins after the release, so: • VOT 50 - 150 milliseconds • For unaspirated stops--voicing begins at the release, so: • VOT 0 - 20 milliseconds • For voiced stops--voicing begins before the release, so: • VOT < 0 milliseconds • (VOT can be negative)
Thai Stops • In stressed onset position, English distinguishes between: • unaspirated and aspirated stops. • Languages like French, Dutch and Spanish distinguish between: • voiced and voiceless unaspirated stops. • Thai splits up the VOT continuum into three parts: • voiced, voiceless unaspirated, voiceless aspirated
English Stop Contrasts • In onset position: • /p/ is voiceless aspirated • /b/ is voiceless unaspirated • In medial position (between voiced segments): • /p/ is voiceless unaspirated • /b/ is voiced • After /s/, in the same syllable: • only voiceless unaspirated stops (no contrast)
English Stop Contrasts 4. In syllable-final position: • vowels preceding /p/ are short • vowels preceding /b/ are longer • /p/ closure tends to be longer than /b/ closure • Moral of the story: • Phonological voiced vs. voiceless contrast in English is abstract • It may exhibit different phonetic manifestations • Phonemes vs. Allophones
Complication #1 • Fricatives and affricates may also be aspirated • In these cases, VOT must be calculated beginning from the offset of sibilance.
Tree vs. Chree • Check ‘em out in Praat
Syllable-Final • Syllable-final obstruents may also be distinguished by aspiration. Examples from Armenian • In this case, voicing does not necessarily resume after aspiration
Syllable-Final Spectrograms release burst aspiration
Practical Point: Pop Filters • When recording speech digitally, the airflow of aspiration can cause “pops” to appear in the recording. • A result of clipping the waveform • If you have some extra cash, this problem can be solved by placing a pop filter in front of the microphone. • Otherwise, make sure the microphone is not directly in front of the speaker’s lips.
Voice Quality • Note that there are three primary types of vocal fold vibration: • modal • vocal folds lightly adducted; flow of air causes periodic opening and closing of folds (“trilling”) • breathy • vocal folds slightly apart; flow of air makes folds “wave” in the wind • creaky • vocal folds tensely adducted; low airflow causes irregular, low frequency voicing
breathy  creaky 
Modal to Creaky [ ]
Voice Quality Movies Source: http://www.ling.mq.edu.au/speech/physiology/movies/fibrescope/index.html
Contrasts • Gujarati contrasts breathy voiced vowels with modal voiced vowels: • Jalapa Mazatec has a three-way contrast between modal, breathy and creaky voiced vowels:
Voiced Aspirated • Some languages distinguish between (breathy) voiced aspirated and voiceless aspirated stops and affricates. • Check out Hindi: