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Acoustics Gk.akoustos “heard, audible" akouein “to hear”

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Presentation on theme: "Acoustics Gk.akoustos “heard, audible" akouein “to hear”"— Presentation transcript:

1 Acoustics Gk.akoustos “heard, audible" akouein “to hear”

2 PIE *(s)keu- “notice, observe” skeu- keu- Gk akouein "to hear” akoustos "heard, audible" WG *skauwojanan OE sceawian “watch” Lat cavere “watch out” cautio “caution” Germanic *hausjan heyra OE hieran hear showskoða

3 3 domains of phonetics articulatory phonetics acoustic phonetics auditory phonetics

4 3 domains of phonetics articulation acoustics audition ))))))))))))))))))) ))))))))))))))))

5 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

6 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

7 “ah ah ah ah”

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11 “ah ah ah ah” Hz = Herz = cps = cycles per second

12 Sentence stresses Sentence stresses are characterised by increased loudness changes of pitch

13 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

14 Waves In most languages, the term 'wave' originally refers to the surface movements of water (bølge, Welle, onde, volná, tonn, aalto, to give some European examples).

15 Waves Waves 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.

16 Waves Many 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.)

17 Transverse and longitudinal waves þverbylgjur og lengdarbylgjur transverse: displacement across the direction of propogation longitudinal: displacement along the direction of propogation

18 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

19 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.

20 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 at ttp://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/eds.gifttp://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/eds.gif in

21 Longitudinal waves ttp://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/eds.gifttp://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/eds.gif %

22 Longitudinal waves A graph of pressure changes at any one place plotted on a time axis looks like a transverse wave pattern

23 Longitudinal waves Sound waves in air are longitudinal waves, but they can be represented in this way as transverse waves x= eardrum / microphone

24 Sine waves Latin sinus 'a curve' regular frequencies simple harmonic motion –pendulum –tuning fork.

25 Sine waves Pure tones. When a soundwave is a pure sine- wave, we hear it as a pure tone. Soundwave of pure middle A, which is 440 Hz.

26 Sine waves Some fairly pure examples: my tuning-fork (pitchfork?) Praat – PK 27 Sep 2009

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28 Sine waves Some fairly pure examples: whistling Praat – PK 27 Sep 2009

29 Complex waves Adding 2 sine equal waves:

30 Complex waves Adding: various frequencies

31 Recorded in SoundEdit between

32 Recorded in Praat 27 Sep 2009

33 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

34 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.

35 “shoe”

36 “fish”

37 Fourier analysis In December 1807, the French physicist and mathematician Jean Baptiste Joseph Fourier ( ) read a memoir on "the propagation of heat in solids" at the French Institute. David A Keston /~davidk/fourier.htm

38 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.

39 Fourier analysis In linguistic acoustics, we find that different vowels have their own typical arrangements of components, which we call formants.

40 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.

41 How Praat computes pitch (make a video)

42 Complex waves Adding 2 sine equal waves:

43 Adding waves with close frequencies

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45 Adding 2 waves, varying the phasing of the second wave

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49 Varying the phasing of identical waves Adding two waves phased alike

50 Varying the phasing of identical waves Phasing of second wave 140°

51 Varying the phasing of identical waves Phasing of second wave 170°

52 Varying the phasing of identical waves phasing of 2nd wave 180°

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55 3 domains of phonetics articulation acoustics audition ))))))))))))))))))) ))))))))))))))))


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