Nasal Acoustics December 8, 2010
For Starters • Take-home quiz issues! • Production Exercise #4 is due at 5 pm. • I’ll send out a link to the production exam, once Production Exercise #4 has been graded. • Friday: (optional) review for the final exam • Reminder--Final Exam info: • Saturday, December 18th, 8:00-10:00 am • Engineering E 239 • After today’s lecture: evaluations of instruction
Nasal Acoustics • The acoustics of nasal stops are quite complex. • Here’s the general pattern of what to look for in a spectrogram for nasals: • Periodic voicing. • Overall amplitude lower than in vowels. • Low frequency first formant. • Higher formants have low intensity. • Formants have broad “bandwidths”. • Let’s account for each of these acoustic characteristics in turn.
Decreased Overall Amplitude [m] [m]
Damping • The decreased overall amplitude of nasals is due to several factors, including 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
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
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 • Damping decreases amplitude… • And spreads energy across a wider range of frequencies. • = increased bandwidth
Bandwidth in Spectrograms F3 of F3 of [m] The formants in nasals have increased bandwidth, in comparison to the formants in vowels.
[l] vs. [n] • Laterals are usually more intense than nasals • less volume, less surface area = less damping • break between vowels and laterals is less clear [ ] [ n ]
Nasal Plosion • One last, random thing about nasals-- • It is possible to “release” an oral stop closure by opening up the velo-pharyngeal port. • The release burst caused thereby is referred to as nasal plosion. • Peter says hidden, sadden, sudden, leaden • with nasal plosion • without nasal plosion • Nasal plosion occurs in “pre-stopped” nasals in Russian: • [dno] “bottom” [dna] “of the day”
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?