1. Sonorant Acoustics
March 4, 2010

2. Singer’s Formant Demo

3. Moving On…
The tube model is also useful in understanding the acoustics of sonorants:
Nasals
Laterals
Approximants
The source/filter characteristics of sonorants are similar to vowels…
with a few interesting complications.
One interesting acoustic property exhibited by (some) sonorants is damping.

4. Damping? Recall that resonance occurs when:
a sound wave travels through an object
that sound wave is reflected...
...and reinforced, on a periodic basis
The periodic reinforcement sets up alternating patterns of high and low air pressure
= a standing wave

5. Resonance in a closed tube

6. Damping, schematized In a closed tube:
With only one pressure pulse from the loudspeaker, the wave will eventually dampen and die out.
Why?
The walls of the tube absorb some of the acoustic energy, with each reflection of the standing wave.

7. Damping Comparison A heavily damped wave wil die out more quickly...
Than a lightly damped wave:

8. Damping Factors The amount of damping in a tube is a function of:
The volume of the tube
The surface area of the tube
The material of which the tube is made
More volume, more surface area = more damping
Think about the resonant characteristics of:
a Home Depot
a post-modern restaurant
a movie theater
an anechoic chamber

9. An Anechoic Chamber

10. Resonance and Recording
Remember: any room will reverberate at its characteristic resonant frequencies
Hence: high quality sound recordings need to be made in specially designed rooms which damp any reverberation
Examples:
Classroom recording (29 dB signal-to-noise ratio)
“Soundproof” booth (44 dB SNR)
Anechoic chamber (90 dB SNR)

11. Spectrograms
classroom
“soundproof” booth

12. Spectrograms
anechoic chamber

13. Inside Your Nose In nasals, air flows through the nasal cavities.
The resonating “filter” of nasal sounds therefore has:
increased volume
increased surface area
 increased damping
Note:
the exact size and shape of the nasal cavities varies wildly from speaker to speaker.

14. Nasal Variability
Measurements based on MRI data (Dang et al., 1994)

15. Damping Effects, part 1
Damping by the nasal cavities decreases the overall amplitude of the sound coming out through the nose.
[m]
[m]

16. Damping Effects, part 2
How might the power spectrum of an undamped wave:
Compare to that of a damped wave?
A: Undamped waves have only one component;
Damped waves have a broader range of components.

17. Here’s Why
100 Hz sinewave +
90 Hz sinewave +
110 Hz sinewave

18. The Result
90 Hz +
100 Hz +
110 Hz
If the 90 Hz and 110 Hz components have less amplitude than the 100 Hz wave, there will be less damping:

19. Damping Spectra
light
medium

20. Damping Spectra
heavy
Damping increases the bandwidth of the resonating filter.
Bandwidth = the range of frequencies over which a filter will respond at .707 of its maximum output.
 Nasal formants will have a larger bandwidth than vowel formants.

21. Bandwidth in Spectrograms
F3 of
F3 of [m]
The formants in nasals have increased bandwidth, in comparison to the formants in vowels.

22. Nasal Formants
The values of formant frequencies for nasal stops can be calculated according to the same formula that we used to calculate formant frequencies for an open tube.
fn = (2n - 1) * c 4L
The simplest case: uvular nasal
The length of the tube is a combination of:
distance from glottis to uvula (9 cm)
distance from uvula to nostrils (12.5 cm)
An average tube length (for adult males): 21.5 cm

23. The Math 12.5 cm fn = (2n - 1) * c 4L L = 21.5 cm c = 35000 cm/sec86
= 407 Hz
F2 = 1221 Hz
F3 = 2035 Hz
9 cm

24. The Real Thing
Check out Peter’s production of an uvular nasal in Praat.
Note: the higher formants are low in amplitude
Some reasons why:
Overall damping
“Nostril-rounding” reduces intensity
Resonance is lost in the side passages of the sinuses.
Nasal stops with fronter places of articulation also have anti-formants.

25. 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
Acoustic jargon:
formants = “poles”
anti-formants = “zeros”

26. Nasal Filter Function formant (pole)
Note: this is a hypothetical function
anti-formant (zero)

27. 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 4L
L = 8 cm
AF1 = / 4*8 = 1094 Hz
AF2 = 3281 Hz
etc.

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

29. Nasal Spectrum
Anti-formant 1  875 Hz
Anti-formant 2  2160 Hz

30. 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

31. [m] vs. [n] [m] [e] [n] [o] AF1 (n) AF1 (m)
Production of [meno], by a speaker of Tsonga
Tsonga is spoken in South Africa and Mozambique

32. Nasal Stop Acoustics: Summary
Here’s the general pattern of what to look for in a spectrogram for nasals:
Periodic voicing.
Overall amplitude lower than in vowels.
Formants (resonance).
Formants have broad bandwidths.
Low frequency first formant.
Less space between formants.
Higher formants have low amplitude.

33. 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?
1 = alveolar
2 = bilabial
3 = velar
1 = velar
2 = alveolar
3 = bilabial

34. 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:
Formants for oral tract.
Formants for nasal tract.
Anti-formants for nasal passageway.
Plus:
Larger bandwidths
Lower overall amplitude

35. Nasal Vowel Movie

36. Chinantec
The Chinantec language contrasts two degrees of nasalization on vowels.
Chinantec is spoken near Oaxaca, Mexico.
Check out the X-ray video evidence….

37. Oral vs. Partly Nasal Note: extra formants + expanded bandwidth…
Tends to smear all resonances together in the frequency dimension.

38. Partly vs. Wholly Nasal

39. !Xoo Oral and Nasal Vowels

40. Nasal Vowel Acoustics
The smearing of vowel formants can obscure F1 (vowel height) differences
high vowels sound low
low vowels sound high
Note: American South “pen” vs. “pin”
French: [le] vs.
[lo] vs.
Nasalization of [æ] is hypothesized to have kick-started to Great Lakes chain shift.
By shoving it perceptually closer to [e]…

41. Measuring Nasality
One method of measuring oral and nasal airflow simultaneously involves using an airflow mask.
The mask contains pressure transducers in separate nasal and oral chambers.

42. Airflow Samples
The airflow mask spits out readings of the amount of air flowing out of the nose and the mouth at the same time.
nasal vowels: concomitant airflow through both mouth and nose
nasal stops: airflow only through nose

43. Vowel Nasalization

44.
Nasometer
Another tool which has been developed for studying the nasalization of vowels (and other segments) is the Nasometer.
The Nasometer uses two microphones to measure airflow through both the mouth and nose at the same time.
We’ll play around with this instrument in the next lab exercise.
(Show up on Tuesday at the phonetics lab!)

45. Laterals
Laterals share some acoustic characteristics with vowels and nasals.
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.

46. Lateral Palatography

47. 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.

48. 17.5 cm
4 cm
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 ( Hz)
Anti-formant arises from a side tube of length  4cm
AF1 = 2125 Hz

49. Laterals in Reality Check out the Mid-Waghi and Zulu laterals in Praat
Mid-Waghi: [alala]