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Acoustics
Gk.akoustos “heard, audible" akouein “to hear”
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PIE*(s)keu- “notice, observe”
skeu-keu-
Gkakouein"to hear”akoustos"heard, audible"
WG*skauwojanan
OE sceawian“watch”
Latcavere“watch out”cautio“caution”
Germanic
*hausjan
heyra
OE hieran
hear show skoða
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3 domains of phonetics
• articulatory phonetics
• acoustic phonetics
• auditory phonetics
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3 domains of phonetics
articulation acoustics audition
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Acoustics and sentence stress
We have seen that sentence stress consists of the prosodic features:
• pitch, length and loudness (Cruttenden 1986:2)
• to which we added vowel quality in Phonetics 1.
• In this slide show we'll consider only pitch and loudness
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Pitch and Loudness
• Pitch is determined by frequency - the speed of vibration of the vocal chords
• Loudness is determined by amplitude - the extent or breadth of vibration of the vocal chords
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“ah ah ah ah”
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“ah ah ah ah”
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0.007760
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0.005171
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“ah ah ah ah”
Hz = Herz = cps = cycles per second
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Sentence stresses
• Sentence stresses are characterised by
• increased loudness
• changes of pitch
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Frequency
• The pitch of a speech sound is determined by the frequency of vocal-chord vibration. Frequency is usually measured in cycles per second (c.p.s) which are also called Hertz (Hz).
• Womens' voices can go up to 400 Hz; children's voices even higher.
• Average male voices range between 80 and 200 Hz
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WavesIn most languages, the term 'wave' originally refers to the surface movements of water (bølge, Welle, onde, volná, tonn, aalto, to give some European examples).
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WavesWaves on water are a true example of natural waveforms, but it was not until the advent of electronic technology that we discovered that a large number of waveforms occur in the physical world.
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WavesMany are on too small a scale to be experienced as waves (sound- and light-waves) while others are too large (earthquakes, weather & climactic patterns, tidal movements, seasonal patterns, planetary movements).
It is in fact possible to analyse a variety of natural and human processes as wave patterns: heartbeats, brain activity, population studies, the market, influenza epidemics, traffic flows (whether or not this always produces a useful analysis is another question.)
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Transverse and longitudinal waves þverbylgjur og lengdarbylgjur
• transverse: displacement across the direction of propogation
• longitudinal: displacement along the direction of propogation
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Transverse waves • to-and-fro movement (or oscillation) across the
direction of propogation, either from side to side or up and down
• Sea waves are transverse waves: the surface of the sea moves up and down as the waves travel over it
Figure 1
Direction of wave movement
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Transverse waves
• If we use the data from this device to plot a graph showing the height of the sea above this stationary point on the sea-bed, we will get a picture in time which looks exactly the same as the spacial movement of the waves.
Figure 1
Direction of wave movement
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Longitudinal waves
• to-and-fro movement in the same direction as the direction of the wave.
• compression & rarifaction (þétting og þan)• travel along the line of the wave-motion
see the animation atttp://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/eds.gif in
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/u11l2d.html
o o o o o o o o o o o o o o o o o o o o o oooooooooo o o o o o o o o o o o o o o o o o o o o o o o o o
Direction of wave movement
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Longitudinal waves
ttp://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/eds.gif %
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Longitudinal waves
• A graph of pressure changes at any one place plotted on a time axis looks like a transverse wave pattern
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Longitudinal waves
• Sound waves in air are longitudinal waves, but they can be represented in this way as transverse waves
Figure 5
x
Figure 6
x= eardrum / microphone
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Sine waves
• Latin sinus 'a curve'
• regular frequencies
simple harmonic motion
– pendulum
– tuning fork. Figure 7
Figure 8
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Sine waves
Pure tones. When a soundwave is a pure sine-wave, we hear it as a pure tone.
Figure 9
Soundwave of pure middle A, which is 440 Hz.
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Sine waves Some fairly pure examples: my tuning-fork (pitchfork?)
Praat – PK 27 Sep 2009
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Sine waves Some fairly pure examples: whistling
Praat – PK 27 Sep 2009
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Complex wavesAdding 2 sine equal waves:
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Complex waves
Adding: various frequencies
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I
A
O
U
Recorded in SoundEdit between 1992-8
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Recorded in Praat 27 Sep 2009
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Reasons for difference: phasing (I think)
Impossible to read the formants from the waveform. This problem is is overcome by Fourier analysis -- which finds the same formants although the the phasing is different.
This comes a few slides down
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periodic and aperiodic: complex soundwaves
• periodicity• not as regular as pure
tones, since each 'period' is slightly different from the previous one
• Human speech-sounds are not pure, but dynamic sounds: their frequency is continually changing, and so is the shape of the sound-wave.
I
A
O
U
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“shoe”
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“fish”
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Fourier analysis
• In December 1807, the French physicist and mathematician Jean Baptiste Joseph Fourier (1768-830) read a memoir on "the propagation of heat in solids" at the French Institute.
David A Keston
www.astro.gla.ac.uk /~davidk/fourier.htm
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Fourier analysis
• The mathematics behind this method of analysis are what are known today as the Fourier Series, a branch of calculus which can be used to calculate the pure sine wave components of a complex wave.
• The idea is that complex periodic waves can be broken down into a (sometimes very large) number of pure waves which when added together produce the complex wave.
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Fourier analysis
• In linguistic acoustics, we find that different vowels have their own typical arrangements of components, which we call formants.
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Fourier analysis
• The basic or fundamental frequency - usually referred to as F0, is the frequency of the greatest period, the complete repetitive cycle. This is the frequency we hear as pitch when we are working with intonation.
I
A
O
U
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How Praat computes pitch
(make a video)
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Complex wavesAdding 2 sine equal waves:
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Adding waves with close frequencies
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Adding waves with close frequencies
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Adding 2 waves, varying the phasing of the second wave
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Adding 2 waves, varying the phasing of the second wave
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Adding 2 waves, varying the phasing of the second wave
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Adding 2 waves, varying the phasing of the second wave
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Varying the phasing of identical waves
• Adding two waves phased alike
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Varying the phasing of identical waves
• Phasing of second wave 140°
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Varying the phasing of identical waves
• Phasing of second wave 170°
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Varying the phasing of identical waves
• phasing of 2nd wave 180°
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3 domains of phonetics
articulation acoustics audition
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