Ling2005 week2:

1. The nature of sound

• Pressure fluctuations in a medium
  • What is pressure?
  • Why do we need a medium for sound waves?
• Sound propogation
  • How does sound travel in a medium?
  • Longitudinal and transverse waves
• Waveforms of some common sounds

2. Types of signals (waves)

• Periodic (repeating) vs. Aperiodic (non-repeating)
  • Cite examples of each type of auditory signal.
  • Can you measure the frequency of both types of wave?
• Continuous vs. Transient signals
  • Cite examples from familiar auditory signals and speech sounds.
• Simple (sinusoidal) vs Complex signals
  • Simple harmonic motion (SHM): Uniform circular motion projected on a plane.
  • Cite examples of SHM
  • The equation for SHM: Displacement (y) = A sin 2.pi./T
  • Why is SHM important?

3. Properties of waves

• Period: Time between wavefronts; time for wave to repeat itself.
  • Symbol: T (Lower case “t” is used for ‘elapsed time’)
  • Measured in: centi-seconds or, more commonly, in milliseconds(msec.)
• Wavelength: Distance between wavefronts:
  • Symbol: (Lambda)
  • Measured in: centimetres
• Frequency: Number of repetitions of a wave per unit time
  • Symbol: f, or F0 (fundamental frequency), when the wave has more than one frequency component.
  • Measured in: Cycles per second; Hertz (Hz); Kilo Hertz (kHz)
  • What is the perceptual correlate of frequency?
  • How is the frequency of a wave related to its period?
• Amplitude: displacement of vibrating particle from equalibrium position
  • Symbol: A = peak amplitude
  • What is the perceptual correlate of amplitude?
  • Instantaneous amplitude/displacement: = a (or 'y' axis value at time = t); 'Peak-to-peak' amplitude.
  • “Average” or RMS (root mean square) amplitude.
  • Why do we need RMS amplitude?
• Phase: the time synchrony between two (or more) waves or the frequency components of a complex wave
  • Symbol: Omega
  • Measured in: degrees or radians
  • Is phase an important property for analysing speech signals?
  • Is the ear sensitive to phase differences?

4. Complex vibrations (waves)

• A complex wave as the sum of a number of sine waves (sinusoids)
• Fundamental frequency of a complex periodic wave:
  • The rate or repetition of the complex wave
  • Symbol: F0
  • The fundamental frequency of a complex wave is the highest common multiple of its component frequecies.
• The effect of phase relations among components on the resultant waveform.
• What is the effect of summing two sinusoids that are 180 degrees out of phase?
• Fourier’s theorum. What did Fourier demonstrate?
• What is the importance of Fourier’s theorum?

5. Waveform and Spectrum

• Two complementary ways of exmining signals
• The timeseries waveform: a temporal representation - "ya"
• The spectrum: a frequency domain representation - "ya"
• The spectrogram: a time and frequency representation of the sound.
• Waveform and Spectral representation of some common periodic signals:
  • sinusoid (simple wave)
  • two sinusoids
  • square wave
• Waveform and spectrum of:
  • Pulse trains
  • Single pulse
  • White noise
    • instantaneous and long-term spectrum
  • The glottal waveform

6. Production of speech sounds

• functional model of vocal tract
• energy source: Airstream
• primary sound source: vocalization
• secondary sound source: turbulence in vocal tract
• resonators:
  • oral and pharyngeal
  • nasal

7. An auditory/acoustic classification of speech sounds

8. Coarticulation

• What are coarticulation effects?
• Anticipatory and 'carry-over' effects
• Explanations for coarticulation effects
• Coarticulation effects and Connected Speech Processes
• Observing coarticulation effects:
  • Impressionistically (phonetic transcription)
  • Instrumentally: e.g.: Palatography, Electropalatography (EPG)
• Coarticulation effects in a Gestural model of Speech Production