Vowel Acoustics, part 2

November 14, 2012

The Master Plan• Acoustics Homeworks are due!

• Today:

• Source/Filter Theory

• On Friday:

• Transcription of Quantity/More Vowels of the World

• There’s also another production exercise due next Wednesday!

• Production of exotic vowels

• Measure your own vowel formants!

Vowel Acoustics• 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

• Also: lip rounding tends to lower both formants.

• A caveat: rounded vowels (like [u] and [o]) are often fronted in modern English.

“Normalcy”

“booed” “bode”

Feeling Minnesota

“booed” “bode”

Looking California

“booed” “bode”

Vowel Diacritics• The IPA contains a few diacritics which are especially relevant to vowels.

• The most important of these is the diacritic for nasalization.

• Ex: = nasalized [e]

• Nasalized vowels are produced by lowering the velum during the production of a vowel

• air flows through both the nose and the mouth

• Contrastive nasal vowels are found in 20% of the world’s languages

Back to French

Nasal Vowel Acoustics• The acoustics of nasal vowels are very complex.

• One general pattern: nasalization expands bandwidths.

• this smears formants

Chinantec Examples

Nasal Vowel Acoustics• Nasalization smears vowel bandwidths, which can obscure F1 (vowel height) differences

• high vowels sound low

• low vowels sound high

• Note: American English “pen” vs. “pin”

• French: [le] vs.

[lo] vs.

Nasal Spreading• Nasalization often spreads from consonants to vowels

• Sundanese (spoken in Indonesia) has a famous pattern of nasal spreading, which is blocked by certain consonants.

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.

http://www.kayelemetrics.com/Product%20Info/6400/6400.htm

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

Source/Filter Theory: The Source

• Developed by Gunnar Fant (1960)

• For speech, the source of sound = complex waves created by periodic opening and closing of the vocal folds

Source Differences

adult male voice

(F0 = 150 Hz)

child voice

(F0 = 300 Hz)

Just So You Know• Voicing, on its own, would sound like a low-pitched buzz.

• Check out the sawtooth wave spectrum:

• Vowels don’t sound like this because the source wave gets “filtered” by the vocal tract.

“Filters”• For any particular vocal tract configuration, certain frequencies will resonate, while others will be damped.

• analogy: natural variation/environmental selection

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

Source + Filter = Output

+

=

A Vowel Spectrum

Note:

F0 160 Hz

F1

F2

F3 F4

Output Example: [i]

• Different vowels are characterized by different formant frequencies.

• These reflect changes in the shape of the sound filter.

• (the vocal tract)

Vowel Spectrum #2: [i]

F0 = 185 Hz

F1

F2 F3

at different pitches

100 Hz 120 Hz

150 Hz

Narrow-Band Spectrogram• A “narrow-band spectrogram” clearly shows the harmonics of speech sounds.

• …but the formants are less distinct.

harmonics

Wide-Band Spectrogram• By changing the parameters of the Fourier analysis, we can get a “wide-band spectrogram”

• This shows the formants better than the harmonics.

formants

Wide-Band Spectrogram• By changing the parameters of the Fourier analysis, we can get a “wide-band spectrogram”

• This shows the formants better than the harmonics.

formants

F1

F2

F3

Wide-Band Spectrogram• By changing the parameters of the Fourier analysis, we can get a “wide-band spectrogram”

• This shows the formants better than the harmonics.

formants

F1

F2

F3

voice bars (glottal pulses)

Spectrographically• This is what it looks like when you change the source independently of the filter.

• The formants stay the same, but the F0 and harmonics change.

The Flip Side• This is what it looks like when you change the filter independently of the source.

• The resonating frequencies change, but the F0 and harmonics stay the same.

More Relevantly• In diphthongs, the filter changes while the source can remain at the same F0.

“Boyd”

• Check out the narrow-band spectrogram…

Women and Men• The acoustics of male and female vowels differ

reliably along two different dimensions:

1. Sound Source

2. Sound Filter

• Source--F0: depends on length of vocal folds

shorter in women higher average F0

longer in men lower average F0

• Filter--Formants: depend on length of vocal tract

shorter in women higher formant frequencies

longer in men lower formant frequencies

Male Formant Averages

200

300

400

500

600

700

800

900

1000

10001500200025003000

F2

F1

[i][u]

[æ]

Female Formant Averages

200

300

400

500

600

700

800

900

1000

10001500200025003000

F2

F1

[i] [u]

[æ]

Combined Formant Averages

200

300

400

500

600

700

800

900

1000

10001500200025003000

F2

F1

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

In Conclusion• Everybody’s vowel space is different.

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

• We identify vowels on the basis of the patterns formed by their formants within that acoustic space.

• F1 determines the height of vowels.

• F2 determines the front/backness of vowels.

• Questions?