Sonorant Acoustics

March 22, 2013

For Starters• Let’s do a perception experiment!

Anti-Formants• For nasal stops, the occlusion in the mouth creates a side cavity.

• This side cavity resonates at particular frequencies.

• These resonances absorb acoustic energy in the system.

• They form anti-formants

Anti-Formant Math• Anti-formant resonances are based on the length of the vocal tract tube.

• For [m], this length is about 8 cm. 8 cm

• fn = (2n - 1) * c

4LL = 8 cm

AF1 = 35000 / 4*8 = 1094 Hz

AF2 = 3281 Hz

etc.

Spectral Signatures• In a spectrogram, acoustic energy lowers--or drops out completely--at the anti-formant frequencies.

anti-formants

Nasal Place Cues• At more posterior places of articulation, the “anti-resonating” tube is shorter.

• anti-formant frequencies will be higher.

• for [n], L = 5.5 cm

• AF1 = 1600 Hz

• AF2 = 4800 Hz

• for , L = 3.3 cm

• AF1 = 2650 Hz

• for , L = 2.3 cm

• AF1 = 3700 Hz

[m] vs. [n]

• Production of [meno], by a speaker of Tsonga

• Tsonga is spoken in South Africa and Mozambique

[m] [e] [n] [o]

AF1 (m)

AF1 (n)

Nasal Stop Acoustics: Summary

• Here’s the general pattern of what to look for in a spectrogram for nasals:

1. Periodic voicing.

2. Overall amplitude lower than in vowels.

3. Formants (resonance).

4. Formants have broad bandwidths.

5. Low frequency first formant.

6. Less space between formants.

7. Higher formants have low amplitude.

• Anti-formants!

Perceiving Nasal Place• Nasal “murmurs” do not provide particularly strong cues to place of articulation.

• Can you identify the following as [m], [n] or ?

• Repp (1986) found that listeners can only distinguish between [n] and [m] 72% of the time.

• Transitions provide important place cues for nasals.

• Repp (1986): 95% of nasals identified correctly when presented with the first 10 msec of the following vowel.

• Can you identify these nasal + transition combos?

Nasalized Vowel Acoustics• Remember: vowels are often nasalized next to a nasal

stop.

• This can obscure formant transitions.

• The acoustics of nasalized vowels are very complex.

• They include:

1. Formants for oral tract.

2. Formants for nasal tract.

3. Anti-formants for nasal passageway.

• Plus:

• Larger bandwidths

• Lower overall amplitude

Nasal Vowel Movie

Chinantec• The Chinantec language contrasts two degrees of nasalization on vowels.

• Chinantec is spoken near Oaxaca, Mexico.

• Check out the X-ray video evidence….

Oral vs. Partly Nasal

• Note: extra formants + expanded bandwidth…

• Tends to smear all resonances together in the frequency dimension.

Partly vs. Wholly Nasal

!Xoo Oral and Nasal Vowels

Laterals• Laterals are produced by constricting the sides of the tongue towards the center of the mouth.

• Air may pass through the mouth on either both sides of the tongue…

• or on just one side of the tongue.

Lateral Acoustics• The central constriction traps the flow of air in a “side branch” of the vocal tract.

• This side branch makes the acoustics of laterals similar to the acoustics of nasals.

• In particular: acoustic energy trapped in the side branch sets up “anti-formants”

• Also: some damping

• …but not as much as in nasals.

• Primary resonances of lateral approximants are the same as those of for vocal tract length of 17.5 cm

• 500 Hz, 1500 Hz, 2500 Hz...

• However, F1 is consistently low (300 - 400 Hz)

4 cm

17.5 cm

• Anti-formant arises from a side tube of length 4cm

• AF1 = 2125 Hz

Laterals in Reality• Check out the Mid-Waghi and Zulu laterals in Praat

Mid-Waghi: [alala]