Stop + Approximant Acoustics

November 30, 2011

Updates• Grading of Production Exercise #3 continues apace.

• Production Exercise #4 has been posted.

• due on Wednesday the 7th

Voiced Aspirated• Some languages distinguish between (breathy) voiced aspirated and voiceless aspirated stops and affricates.

• Check out Hindi:

[phal]

Hindi

Bengali

[dhol]

voiced + breathy aspirated

voiced + aspirated

Zhu|hoasi Stop Contrasts

• Zhu|hoasi is spoken in northern Namibia.

• Last but not least, Korean makes an interesting distinction between “emphatic” (or fortis) obstruents and unaspirated (lenis) and aspirated obstruents.

What’s going on here?• A variety of things are going on in the articulation of

fortis consonants in Korean.

1. Glottis does not open as wide as in lenis stops.

Voicing begins more quickly after stop release

2. Vocal folds are more tense than in lenis stops.

3. Increased airflow in fortis stops.

Higher F0 after stop release.

A Basic Distinction• Vowels

• Relatively unconstricted flow of air through vocal tract (above the glottis)

• Shape (filter) the source of sound made at the glottis

• Consonants

• Completely or severely constricted flow of air through vocal tract (above the glottis)

• Create a source of sound at the constriction (e.g., release bursts, turbulence)

• Voicing may be difficult

• Note: this is a phonological distinction, not a phonetic one.

Obstruents and Sonorants• Phonologically speaking, there are also different kinds of consonants.

• One important distinction is between obstruents and sonorants.

• Obstruents

• Stops, fricatives, affricates

• Obstruct flow of air through the vocal tract so much that voicing is difficult

• Sonorants

• Nasals, approximants (glides, liquids), trills, flaps

• Allow air to flow freely through vocal tract so that resonance (voicing) is still possible

Stop Acoustics Overview• Stages of Stop Production

1. Closing

2. Closure

3. Release

4. Opening

• Acoustic Cues for Place of Articulation

1. Formant transition out of vowel

2. Closure voicing {or nothing}

3. Release burst

4. Formant transition into vowel

Release Bursts• The acoustic characteristics of a stop release burst tend to resemble those of a fricative made at the same place of articulation.

• Ex: labial release bursts have a very diffuse spectrum, just like bilabial and labio-dental fricatives.

[p] burst

Release Bursts: [t]• Alveolar release bursts tend to lack acoustic energy at the bottom of the spectrum.

• To some extent, higher frequency components are more intense.

[t] burst

Release Bursts: [k]• Velar release bursts are relatively intense.

• They also often have a strong concentration of energy in the 1500-2000 Hz range (F2/F3).

• There can often be multiple [k] release bursts.

[k] burst

Closure Voicing• During the stop closure phase, only low frequency information escapes from the vocal tract (for voiced stops)

• “voicing bar” in spectrogram

• analogy: loud music from the next apartment

Armenian:

[bag]

• This acoustic information provides hardly any cues to place of articulation.

[bag] vs. [bak]• From Armenian (another language from the Caucasus)

[bag] [bak]

Formant Transitions• The resonant frequencies of the vocal tract change as stop gestures enter or exit the closure phase.

• Ex: Formant frequencies usually decrease in making the transition from bilabial stop to vowel (or vice versa)

Formant Transitions: alveolars

• For other places of articulation, the type of formant transition that appears is more complex.

• From front vowels into alveolars, F2 tends to slope downward.

• From back vowels into alveolars, F2 tends to slope upwards.

[hid]

[hæd]

Formant Locus• Whether in a front vowel or back vowel context...

• The formant transitions for alveolars tend to point to the same frequency value. ( 1650-1700 Hz)

• This (apparent) frequency value is known as the locus of the formant transition.

• According to one theory of perception...

• the locus frequency can be used by listeners to reliably identify place of articulation.

Velar Transitions• Velar formant transitions do not always have a reliable locus frequency for F2.

• Velars exhibit a lot of coarticulation with neighboring vowels.

• Fronter (more palatal) next to front vowels

• Locus is high: 1950-2000 Hz

• Backer (more velar) next to back vowels

• Locus is lower: < 1500 Hz

• F2 and F3 often come together in velar transitions

• “Velar Pinch”

The Velar Pinch

[bag] [bak]

Fricative Transitions• You get transition cues for fricatives at different places of articulation, too.

• American :

tongue tip between teeth

• British :

tongue tip behind upper teeth

• has a little bit of a transition cue

Transitions

Approximants• Approximants = one articulator is close to another, but

without producing audible turbulence.

• They come in two flavors:

1. Glides (English [w], [j])

2. Liquids (English , [l])

• This distinction is also phonological…

• Glides are essentially high-vowel articulations which are not in a syllabic peak.

• In English, liquids may form syllables (or syllable peaks).

Glides• Each glide corresponds to a different high vowel.

Vowel Glide Place

[i] [j] palatal (front, unrounded)

[u] [w] labio-velar (back, rounded)

[y] labial-palatal (front, rounded)

velar (back, unrounded)

Glide Examples• French contrasts palatal, labio-palatal and labio-velar glides:

• Japanese has velar vowels, but not necessarily velar glides...

Glide Acoustics• Glides are shorter than vowels

• They also tend to lack “steady states”

• and exhibit rapid transitions into (or from) vowels

• hence: “glides”

• Also: lower in intensity

• especially in the higher formants

[j] vs. [i]

[w] vs. [u]

Vowel-Glide-Vowel

[iji] [uwu]

More Glides

[wi:] [ju:]