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05 Prosodic acoustics

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05 Prosodic acoustics Powered By Docstoc
					               Acoustics
Gk.akoustos “heard, audible"
  akouein “to hear”
                              PIE
                   *(s)keu- “notice, observe”

           keu-                          skeu-

Gk                   Germanic           WG
akouein              *hausjan           *skauwojanan
"to hear”
akoustos
"heard, audible"       heyra             OE sceawian
                                         “watch”
 Lat                   OE hieran
 cavere
 “watch out”            hear              show         skoða
 cautio
 “caution”
      3 domains of phonetics
• articulatory phonetics



• acoustic phonetics



• auditory phonetics
  3 domains of phonetics
articulation      acoustics          audition



               )))))))))))))))))))
 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
         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
“ah ah ah ah”
“ah ah ah ah”
0.007760
0.005171
“ah ah ah ah”




   Hz = Herz = cps = cycles per second
         Sentence stresses
• Sentence stresses are characterised by
•   increased loudness
•   changes of pitch
              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
                 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).
                 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.
                    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.)
Transverse and longitudinal waves
           þverbylgjur og lengdarbylgjur

• transverse: displacement across the
  direction of propogation



• longitudinal: displacement along the
  direction of propogation
           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
            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.
             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.gif in
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/u11l2d.html
                     Longitudinal waves




ttp://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/eds.gif %
         Longitudinal waves
• A graph of pressure changes at any one place
  plotted on a time axis looks like a transverse
  wave pattern
          Longitudinal waves
• Sound waves in air are longitudinal waves, but
  they can be represented in this way as
  transverse waves


                           x= eardrum / microphone




                                 Figure 6
                    Sine waves
• Latin sinus 'a curve'
• regular frequencies
                    simple harmonic motion

   – pendulum
   – tuning fork.




                        Figure 8
                  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.
                Sine waves
Some fairly pure
examples: my tuning-fork
(pitchfork?)




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




                                       Praat – PK 27 Sep 2009
          Complex waves
Adding 2 sine equal waves:
          Complex waves
Adding: various frequencies
Recorded in SoundEdit between 1992-8
Recorded in Praat 27 Sep 2009
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
     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.
“shoe”
“fish”
              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
            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.
            Fourier analysis
• In linguistic acoustics, we find that different
  vowels have their own typical
  arrangements of components, which we
  call formants.
               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.
   How Praat computes pitch
(make a video)
          Complex waves
Adding 2 sine equal waves:
Adding waves with close
      frequencies
Adding waves with close
      frequencies
Adding 2 waves, varying the
phasing of the second wave
Adding 2 waves, varying the
phasing of the second wave
Adding 2 waves, varying the
phasing of the second wave
Adding 2 waves, varying the
phasing of the second wave
  Varying the phasing of identical
              waves
• Adding two waves phased alike
  Varying the phasing of identical
              waves
• Phasing of second wave 140°
  Varying the phasing of identical
              waves
• Phasing of second wave 170°
  Varying the phasing of identical
              waves
• phasing of 2nd wave 180°
  3 domains of phonetics
articulation      acoustics          audition



               )))))))))))))))))))

				
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