Visualization of sound acoustic bacics

1. ACOUSTIC PHONETICS
NOTES BY JUNAID AMJED
LECT. ENGLISH DEPT.
IMIT COLLEGE
JUNAIDAMJED@GMAIL.COM
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2. INTRODUCTION
Acoustic phonetics is the study of the acoustic characteristics of speech,
including an analysis and description of speech in terms of its physical
properties, such as frequency, intensity, and duration.
Descriptions of speech sounds in these terms date back as far as 1830
(Willis), but the invention of the sound spectrograph (1945) was the major
technological breakthrough that made the analysis and visualization of the
speech signal possible.
Acoustic Analysis
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3. INTRODUCTION
Subsequent developments in digital signal processing, most notably the discrete Fourier
transform, have made it possible to conduct all acoustic analyses with a basic microcomputer.
Rousselot (b. 1846–d. 1924) is widely regarded as the “father of experimental phonetics.”
Rousselot applied the kymograph to the study of speech. The kymograph, invented in the 1840s
by Ludwig, was originally used for measuring blood pressure and other physiological processes.
Rousselot
For speech, the kymograph consisted of a rotating drum covered with paper coated with
soot; speakers spoke into a rubber tube and the sound vibrations were captured by a
stylus that registered the variations in air pressure, from which duration, intensity, and
pitch could be measured.
kymograph
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4. INTRODUCTION
Edison’s invention of the phonograph in 1877 was of crucial importance since it was the first
device that allowed the recording and reproduction of sound. This invention meant that
speech was no longer a fleeting event but could be repeatedly heard and analyzed. A number
of researchers developed additional devices to visualize and analyze the sound waveforms,
including Hermann, Scripture, and Verner. Although the speech waveform (oscillogram) is the
basis of all acoustic speech research, it is rarely used as a source. One important reason is that
it is “too rich” since it contains information about frequency, intensity, and phase of the signal
components, while human perception disregards the latter. Hence, the spectrogram provides
a better representation.
Edison with his phonograph in 1877
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5. PRACTICAL WORK
WAVEFORMS OF THE VOWEL /A:/ AND THE CONSONANT /S/
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6. PRACTICAL WORK
Acoustic Potencies Auditory Phonetics
Fundamental frequency (Hz) Pitch (how high or low do we
perceive a sound)
Intensity (dB) Loudness (how loud or soft the
reception of sound is)
Duration (t) Speech tempo (how fast or
slow we receive a sound signal)
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7. PRACTICAL WORK
Amplitude
The amplitude is simply a displacement of the vibrating medium from
its rest position.
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8. PRACTICAL WORK
Amplitude
The amplitude of a wave refers to the maximum amount of
displacement of a particle on the medium from its rest position. In a
sense, the amplitude is the distance from (positives Maximum)
position. Similarly, the amplitude can be measured from (negatives
Maximum) position.
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9. PRACTICAL WORK
Fundamental Frequency
•The term fundamental frequency stands for the course of the lowest
frequency in a harmonic vibration, therefore it is also called F0. •„Frequency is
a technical term for an acoustic property of a sound –namely the number of
complete repetitions (cycles) of variations in air pressure occurring in a
second“ (Ladefoged1975, 162)
•the fundamental frequency is the lowest frequency of all other sinus
components in a spectrum •therefore it is called F0 •its whole-
numbered multiples (2x, 3x, 4x,...) are the so-called harmonic.
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10. WHERE ARE ALL THE OTHER FREQUENCIES PRODUCED?
•all frequencies that you find a speech signal come from the larynx
•when we look at the vocal tract as a cylindrical pipe which is
closed at one end (glottis) and open at the other end (mouth) its
wavelength is four times its length •a female vocal tract is about
15 cm long, which means that its wavelength is 60 cm •at about
35°C sound travels at about 352 m/sec
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11. SCHEMATIC VOCAL TRACT
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12. •acoustically the vocal tract is not a very good pipe •energy is dampened in every
frequency of the source signal (coming from the larynx) •what is not dampened so
much are the resonance frequencies, which show as dark shadings in the
spectrogram
•the laryngeal signal has many higher harmonics which means that energy can also
be found in higher frequencies than simply the fundamental frequency •as said
before, the vocal tract dampens certain frequencies more and others less
(depending on the formation of the articulators) •these resonance frequencies are
called formants
•formants are a property of the vocal tract and completely independent from any
source signal (it does not matter whether there is a source signal or not!!!)
•try this: whisper the following: heed, hid, head, had, hod, hawed, hood, who‘d
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13. Formants
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14. •The first two formants F1 and F2 are important for the intelligibility of
vowels
•Their position characterizes the spoken vowel.
•In order to understand each other, it is important that these formants are
similar in every speaker
Formants
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15. ”
“I cannot teach anybody anything. I can only make them
think
― Socrates
NOTES BY JUNAID AMJED
Source: Acoustic theory of speech production.
Acoustic phonetics. Cambridge, MA: MIT Press.
Visible speech. New York: D. Van Nostrand.
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