Sonorant Acoustics March 24, 2009

Announcements and Such Collect course reports Give back homeworks Hand out new course project guidelines

On the Horizon Today: acoustics of sonorants plus a perception experiment Thursday: more sonorant and stop acoustics plus an introduction to the motor theory of perception Next Tuesday: perception homework due stop + fricative acoustics Next Thursday: Articulatory physiology Static palatography demo

Vowels and Sonorants So far, we’ve talked a lot about the acoustics of vowels: Source: periodic openings and closings of the vocal folds. Filter: characteristic resonant frequencies of the vocal tract (above the glottis) Today, we’ll talk about the acoustics of sonorants: Nasals Laterals Approximants The source/filter characteristics of sonorants are similar to vowels… with a few interesting complications.

Obstruents and Sonorants Sonorants are so called because they: allow air to flow freely through vocal tract so that resonance (of voicing) is still possible = consonants that resonate In contrast, obstruents: obstruct flow of air through the vocal tract so much that voicing is difficult to maintain include stops, fricatives, affricates. Sonorants do restrict the flow of air in the vocal tract more than vowels… but not as much as obstruents.

Damping One interesting acoustic property exhibited by (some) sonorants is 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

Resonance in a closed tube

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.

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

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

An Anechoic Chamber

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)

Spectrograms classroom “soundproof” booth

Spectrograms anechoic chamber

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.

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

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.

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

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

Damping Spectra light medium

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.

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

Nasal Formants The values of formant frequencies for nasal stops can be calculated according to the same formula that we used for to calculate formant frequencies for an open tube. f n = (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 nares(12.5 cm) An average tube length (for adult males): 21.5 cm

The Math 12.5 cm 9 cm f n = (2n - 1) * c 4L L = 21.5 cm c = cm/sec F1 = = 407 Hz F2 = 1221 Hz F3 = 2035 Hz

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 “Nare-rounding” reduces intensity Resonance is lost in the side passages of the sinuses. Nasal stops with fronter places of articulation also have anti-formants.

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 f n = (2n - 1) * c 4L L = 8 cm AF1 = / 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.

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

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.

Nasometer A 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.

More Nasometer The Nasometer 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