Transcript Week 2 - University of Pennsylvania

LING 001 Introduction to Linguistics
Fall 2010
Sound Structure I:
Phonetics
Acoustic phonetics
Jan. 27
Make vowel sounds from household materials
Buzzing sound
+
Resonators
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
+
+
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
From Mark Huckvale:
http://www.phon.ucl.ac.uk/home/mark/vowels
LING 001 Introduction to Linguistics, Fall 2010
=
Vowels
=
=
[a]
[i]
2
The source in speech production
• The production of speech consists of two kinds of operations:
(1) the generation of sound sources (the raw material), and (2)
the processing/resonating of these sources by the vocal tract
(the resonator).
• Vocal fold vibration generates buzzing sound, which is the raw
material (source) for producing vowel sounds.
LING 001 Introduction to Linguistics, Fall 2010
3
The vibration of the vocal folds
• The aerodynamics of vocal fold vibration:
With the glottis (the space between the vocal folds) closed and
an airstream issuing from the lungs, the excess pressure below
the glottis (sub-glottal pressure) forces the vocal folds apart; the
air passing between the folds generates a Bernoulli force that
quickly closes the glottis. The sub-glottal pressure builds up
again, forcing the vocal folds apart again.
• The vibration of the vocal folds are periodic. The
frequency of the vibration is determined by the air
pressure in the lungs and by the vocal folds mechanical
properties.
LING 001 Introduction to Linguistics, Fall 2010
4
Periodic and frequency
• Vocal fold vibration is a complex periodic motion, it can be
decomposed into many Simple Harmonic Motions.
• Simple Harmonic Motion is the simplest periodic motion, in
which a body oscillates about an equilibrium position (rest
position) in a sinusoidal pattern. Tuning forks are such an
example.
LING 001 Introduction to Linguistics, Fall 2010
5
Simple Harmonic Motion
• Properties of Simple Harmonic Motion:
displacement: momentary distance from
the rest point
cycle: one complete oscillation
amplitude: maximum displacement
frequency: number of cycles per second (Hz)
period: number of seconds per cycle
• What is the difference?
LING 001 Introduction to Linguistics, Fall 2010
6
7
Spectrum
• A complex periodic motion can be represented as a spectrum
showing:
• Frequency of each simple harmonic component on the x-axis
• Amplitude of each simple harmonic component on on the y-axis
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
LING 001 Introduction to Linguistics, Fall 2010
The source spectrum in speech production
•
•
As the vocal folds open and close, puffs of air flow through the glottal
opening. The frequency of these pulses determines the fundamental
frequency (F0) and contributes to the perceived pitch of the produced
sound.
Besides F0, the glottal air flow also contains a large number of
harmonics (overtones), whose frequencies are integer multiples of F0.
The amplitude of the harmonics decreases gradually.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
LING 001 Introduction to Linguistics, Fall 2010
8
Vocal tract is a resonator
•
•
The vocal tract is a resonator. The resonance frequencies of the vocal
tract, called formants, depend on its shape. The first resonance
frequency is F1, the second resonance frequency is F2, and so on.
The first two or three formants (their frequencies, not amplitudes) are
most important in speech communication.
LING 001 Introduction to Linguistics, Fall 2010
9
Final product: vowels
•
The presence of the formats disrupts the uniformly sloping envelop of
the source spectrum, imposing peaks at the formant frequencies.
Formant frequencies determine vowel quality (/i/ vs. /a/ vs. /u/ etc.)
Vowel spectrum
Vocal tract resonance
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Source spectrum
LING 001 Introduction to Linguistics, Fall 2010
10
Acoustic vowel space
LING 001 Introduction to Linguistics, Fall 2010
11
12
Vowel formants
• Vowel height is closely related to the first formant frequency:
low vowels -> higher F1
• Vowel frontness/backness is closely related to the second
formant frequency:
front vowels -> higher F2
• Formant frequencies of American English vowels (average):
/i/
/a/
/u/
Male
F1 270Hz
F1 730Hz
F1 300Hz
F2 2290Hz
F2 1090Hz
F2 870Hz
Female
F1 310Hz
F1 850Hz
F1 370Hz
F2 2790Hz
F2 1220Hz
F2 950Hz
LING 001 Introduction to Linguistics, Fall 2010
Measuring vowel formants
•
Formants can be displayed by computing a spectrogram, showing the
energy in the signal at different frequencies.
Spectrograms are a plot of the intensity of the frequency content of a
signal as time progresses. The y-axis is frequency, the x-axis is time,
and the intensity is shown on a grey-scale.
•
Praat: doing phonetics by computer. http://www.fon.hum.uva.nl/praat/
•
LING 001 Introduction to Linguistics, Fall 2010
13
The acoustics of consonants
• The sources of consonant sounds are either turbulent airflow
(fricatives) or release of a compressed air behind a closure
(stops). The sources are aperiodic, noises.
Note: White noise contains an equal distribution of energy spread over
all frequencies, just as white light is composed of all of the colors of
the spectrum of visible light.
• The resonator is the front cavity, i.e., the part of the oral cavity
that is in front of the constriction place. The nasal cavity is used
as a resonator in producing nasal sounds.
LING 001 Introduction to Linguistics, Fall 2010
14
15
Fricatives
•
Fricatives have relatively long durations of noise, and it is this lengthy
interval of aperiodic energy that distinguishes fricatives as a sound
class. [s, ʃ] have more energy than [f, θ].
1
0
-1
0
4.477
Time (s)
6000
F
TH
S
SH
0
0
4.477
Time (s)
LING 001 Introduction to Linguistics, Fall 2010
16
Stops
•
Stops are dynamic, it has a series of ‘articulatory postures’:
Gap: during closure, the only possible source is voicing (shown as a voice bar).
Burst: a transient noise produced when the oral closure is released
Aspiration: a diffuse noise generated at the larynx and possibly the lower pharynx.
Its spectrum resembles that for the fricative [h].
•
[tie], [dye], [style].
5000
4000
Aspiration
3000
Gap
2000
1000
Burst
0
0
Time (s)
LING 001 Introduction to Linguistics, Fall 2010
2.963
Voice bar
VOT
•
To further distinguish voiced/voiceless and aspirated/unaspirated, we
can use Voice Onset Time (VOT).
•
VOT is the duration of the period of time between the release of a
plosive/stop and the beginning of vocal fold vibration. This period is
usually measured in milliseconds (ms).
•
It is useful to distinguish at least three types of VOT which are shown
in the schematic diagram below:
LING 001 Introduction to Linguistics, Fall 2010
17
Speech prosody
• Segments characterize speech sounds. Suprasegmental features
(prosody) superimpose on segments or segmental sequences.
• Acoustic cues of prosody:
Pitch, determined by fundamental frequency
Length, determined by duration
Loudness, determined by amplitude
• Stress, tone, intonation, rhythm, etc.
LING 001 Introduction to Linguistics, Fall 2010
18
Tones
• Tone languages use pitch to make lexical contrasts (to
distinguish words).
• contour tones (predominating in Chinese and the languages of
southeast Asia): The tones are made up of dynamic pitch
changes.
• Register tone (predominating in African languages). The tones
are made up of a few pitch registers: high, low, and maybe mid.
LING 001 Introduction to Linguistics, Fall 2010
19
Intonation in English
A: What types of foods are a good source of vitamins?
B1: Legumes are a good source of vitamins.
B2: Legumes are a good source of vitamins.
A: I’d like to fly to Davenport, Iowa on TWA.
B: TWA doesn’t fly there ...
B1: They fly to Des Moines.
B2: They fly to Des Moines.
A1: I met Mary and Elena’s mother at the mall yesterday.
A2: I met Mary and Elena’s mother at the mall yesterday.
LING 001 Introduction to Linguistics, Fall 2010
20
Intonation in English
400
350
300
250
200
150
100
50
legumes are a good source of VITAMINS
400
350
300
250
200
150
100
50
LEGUMES are a good source of vitamins
LING 001 Introduction to Linguistics, Fall 2010
21
Intonation in Mandarin Chinese
•
Interaction between tone and intonation
LING 001 Introduction to Linguistics, Fall 2010
22
Rhythm
•
Rhythm refers to the temporal organization of speech elements. It
depends on many factors.
•
At the segmental level, for example, vowels are longer before
voiced stops than before voiceless ones. The effect is very large in
English (bad vs. bat), but smaller in many other languages such as
French.
•
At the level of syllables, languages have different phonotactic
constraints on syllable shape. For example, many dialects of
Chinese allow only alveolar and velar nasals in the coda position.
LING 001 Introduction to Linguistics, Fall 2010
23
Rhythm
•
In natural speech, over 70% of French and Spanish syllables were
open (e . g ., CV and V) , while more than 50% of English syllables
were closed (e . g ., CVC and VC).
• In Hawaiian there is never more than a single consonant
between any two vowels, but in English there can be seven,
as in texts spread. In Polish there are even more:
LING 001 Introduction to Linguistics, Fall 2010
24