From Resonance to Vowels March 13, 2012 Fun Stuff (= tracheotomy) Peter Ladefoged: “To record the...

From Resonance to Vowels

March 13, 2012

Fun Stuff (= tracheotomy)Peter Ladefoged: “To record the pressure of the air associated with stressed as opposed to unstressed syllables we need to record the pressure below the vocal folds. A true recording of the subglottal pressure can be made only by making a tracheal puncture.This is a procedure that must be performed by a physician. A local anesthetic is applied both externally and inside the trachea by means of a fine needle. A larger needle with an internal diameter of 2 mm can then be inserted between the rings of the trachea as shown in figure 3.3”

Figure 3.3

“As you can see from my face it is not at all painful. But it is not a procedure that can be carried out in fieldwork situations.”

Somewhat Less Fun• Korean stops homework to hand back…

• Mystery spectrogram reading exercise #2!

Stopping by woods on a snowy evening

Whose woods these are I think I know.

His house is in the village though.

He will not see me stopping here

To watch his woods fill up with snow.

My little horse must think it queer

To stop without a farm house near

Between the woods and frozen lake

The darkest evening of the year.

Robert Frost (1874-1963)

He gives his harness bells a shake

To ask if there is some mistake.

The only other sound’s the sweep

Of easy wind and downy flake.

The woods are lovely, dark and deep.

But I have promises to keep,

And miles to go before I sleep--

And miles to go before I sleep.

Stopping by woods on a snowy evening

Robert Frost (1874-1963)

Vowel Resonances

• The series of harmonics flows into the vocal tract.

• Those harmonics at the “right” frequencies will resonate in the vocal tract.

• fn = (2n - 1) * c

4L

• The vocal tract filters the source sound

lipsglottis

“Filters”• In speech, the filter = the vocal tract

• This graph represents how much the vocal tract would resonate for sinewaves at every possible frequency:

• The resonant frequencies are called formants

Source + Filter = Output

+

=

This is the source/filter

theory of speech production.

Source + Filter(s)

Note:

F0 160 Hz

F1

F2

F3 F4

Schwa at different pitches

100 Hz 120 Hz

150 Hz

More Than Schwa

• Formant frequencies differ between vowels…

• because vowels are produced with different articulatory configurations

Remember…• Vowels are articulated with characteristic tongue and lip shapes.

Vowel Dimensions• For this reason, vowels have traditionally been

described according to four (pseudo-)articulatory parameters:

1. Height (of tongue)

2. Front/Back (of tongue)

3. Rounding (of lips)

4. Tense/Lax

= amount of effort?

= muscle tension?

The Vowel Space

o

The Vowel Space

Formants and the Vowel Space• It turns out that we can get to the same diagram in a different way…

• Acoustically, vowels are primarily distinguished by their first two formant frequencies: F1 and F2

• F1 corresponds to vowel height:

• lower F1 = higher vowel

• higher F1 = lower vowel

• F2 corresponds to front/backness:

• higher F2 = fronter vowel

• lower F2 = backer vowel

Male Formant Averages

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1000

10001500200025003000

F2

F1

[i][u]

[æ]

(From some old phonetics class data)

Female Formant Averages

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10001500200025003000

F2

F1

[i] [u]

[æ]


Combined Formant Averages

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500

600

700

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10001500200025003000

F2

F1


Women and Men• Both source and filter characteristics differ reliably between men and women

• F0: depends on length of vocal folds

shorter in women higher average F0

longer in men lower average F0

• Formants: depend on length of vocal tract

shorter in women higher formant frequencies

longer in men lower formant frequencies

Prototypical Voices• Andre the Giant: (very) low F0, low formant frequencies

• Goldie Hawn: high F0, high formant frequencies

F0/Formant mismatches• The fact that source and filter characteristics are independent of each other…

• means that there can sometimes be source and filter “mismatches” in men and women.

• What would high F0 combined with low formant frequencies sound like?

• Answer: Julia Child.

F0/Formant mismatches• Another high F0, low formants example:

Roy Forbes, of Roy’s Record Room (on CKUA 93.7 FM)

• The opposite mis-match =

Popeye: low F0, high formant frequencies

Back to Vowels• A vowel space is defined by a speaker’s range of first formant (F1) and second formant (F2) frequencies.

• …but everybody’s vowel space is different.

• Vowels contrast with each other in terms of their relationships within that acoustic space.

• F1 determines the “height” of vowels.

• F2 determines the “front/backness” of vowels.

• Question:

• How does the way that vowels are produced…

• Determine their acoustic characteristics?

Articulation to Acoustics• Last time, we calculated the formant values for “schwa”, or a neutral vowel.

• Theoretical values (vocal tract length = 17.5 cm)

F1 = 500 Hz

F2 = 1500 Hz

F3 = 2500 Hz

• My values:

F1 = 500 Hz

F2 = 1533 Hz

F3 = 2681 Hz

F4 = 3498 Hz

With a neutral vowel, we’re somewhere in the middle of the acoustic vowel space.


200

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10001500200025003000

F2

F1

Q: How do we get to the corners of the space?

Perturbation Theory• There are two important theories that answer this question.

• The first of these is Perturbation Theory.

• Remember: formants are resonances of the vocal tract.

• These resonances are the product of standing waves in the resonating tube of the articulatory tract.

lipsglottis

What’s the Big Idea?• Chiba and Kajiyama (1941):

• Formant frequencies can be changed by perturbing the airflow of the standing waves in the vocal tract

• Idea #1: velocity of standing waves is inversely related to pressure

• Sort of like the Bernoulli Effect

Standing Waves in the Vocal Tract

• Remember:

• Vocal tract is a tube with one open end at the lips.

• So:

• Pressure node at the lips

• Pressure anti-node at the glottis

• …for all potential standing waves

• This translates into:

• Velocity anti-node at the lips

• Velocity node at the glottis

Standing Waves in the Vocal Tract

F1 F2

• Diagrammed in terms of velocity:

The Big Idea, part 2• Idea #2: constriction at (or near) a velocity anti-node decreases frequency

• The constriction slows the velocity down

• constriction at a pressure node decreases frequency

• Idea #3: constriction at (or near) a velocity node increases frequency

• The constriction increases the pressure

• This enhances airflow

• constriction at a pressure anti-node increases frequency

Here’s the goal• Let’s figure out how we can perturb the airflow in the articulatory tract to get to the corners of the vowel space.

• We need to:

• Lower F1 and raise F2 --> high, front vowels

• Lower F1 and lower F2 --> high, back vowels

• Raise F1 and raise F2 --> low, front vowels

• Raise F1 and lower F2 --> low, back vowels

• Let’s consider them each in turn…

F1

• Velocity node at glottis

• Velocity anti-node at lips

• To lower F1:

make a constriction closer to the lips than to the glottis

• To raise F1:

make a constriction closer to the glottis than to the lips

F2

• Velocity nodes at:

palate

glottis

• Velocity anti-nodes at:

lips

pharynx

F2

• To raise F2, make a constriction at the:

palate

glottis

• To lower F2, make a constriction at the:

lips

pharynx

1. High, Front Vowels

• Lower F1 and raise F2

• Where should we make a constriction(s)?


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F2

F1




• To lower F1:




• To lower F1:

constrict close to lips




• To lower F1:


• To raise F2:




• To lower F1:


• To raise F2:

constrict at palate

2. High, Back Vowels

• = Lower F1 and lower F2



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F2

F1




• To lower F1:




• To lower F1:

constrict at lips




• To lower F1:

constrict at lips

• To lower F2:




• To lower F1:

constrict at lips

• To lower F2:

constrict at lips

constrict at “pharynx”

• Note: these vowels are usually rounded

From Resonance to Vowels March 13, 2012 Fun Stuff (= tracheotomy) Peter Ladefoged: “To record the...

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