Acoustics: Information and demos

This page contains acoustics demos that we will use in class discussion. Practicing with them will also help you master the information from the assigned readings.

Contents of this page:

• I. Basic acoustics (1): Simple waves
• II. Basic acoustics (2): Complex waves
• III. Basic acoustics (3): Standing waves and resonances
• IV. The source-filter model of speech production
• V. Modeling formant frequencies: Vowels

At the end of this page, there are also links to additional information about waves and acoustics.

To return to this page after using one of the demos, use the "Back" button on your browser.

I. Basic acoustics (1): Simple waves

• Demo #1 (silent animation): Examples of waves propagating through their medium
  Dan Russell, Penn State University

• Demo #2 (silent animation): Sound waves propagated by a tuning fork (in "Figure 3")
  Dan Russell, Penn State University

• Demo #3 (silent animation): Graphing a wave in time vs. space
  Dan Russell, Penn State University
  • You do not need to learn the formula at the top of the page.
  • Key point to understand: How are the two graphs at the bottom different from each other? How are they related to the graph in the middle of the page?

• Demo #4 (.wav file): Pure tones at different frequencies (200 Hz-475 Hz)
  Each successive tone is 25 Hz higher in frequency. Does increasing the frequency by equal amounts produce tones that are equal steps apart in perceived pitch?
  H. Timothy Bunnell, University of Delaware

II. Basic acoustics (2): Complex waves

• Demo #5: Sound quality
  Compare these two sounds. Each has a frequency of 200 Hz.     [ Sound #1 ]     [ Sound #2 ]
  • These sounds differ in sound quality (also called timbre). A difference in (perceptual) sound quality is caused by a difference in (physical) wave shape.
  • Open these two sound files in Praat and have a look at how the wave shapes differ.

    Supplemental information: Here is the web page that the above two sounds are taken from. It reviews basic wave properties and discusses how complex waves are formed from simple waves. You might find this a useful alternative presentation of this material, which is also covered in the textbook readings.

    H. Timothy Bunnell, University of Delaware

• Demo #6: Adding waves together
  A complex wave of any shape can be broken down into a set of simple (sine) waves that, when added together, produce the complex wave. These simple waves are called the components of the complex wave.

  This demo allows you to draw individual sine waves (by specifying amplitude and frequency) and add them together to form a complex wave.
  From the Zona Land section on waves

• Demo #7: "Violin" string
  Another example of how simple waves combine to create complex waves. A vibrating string, as on a violin, can vibrate in multiple ways at once. These mode of vibration are called resonances (or sometimes harmonics); we'll see more on this topic soon.

  For now, just look at the relationship between the five simple waves (shown in colors), and the complex wave they combine to create (white). Uncheck some of the colored boxes to remove some of the simple waves, and note how the shape of the complex wave changes when you do this. (For now, don't worry about the text on this web page; just focus on the animation.)
  From the Zona Land section on waves

• Demo #8: Spectra
  The spectrum of a complex wave is a graph that shows the frequency and amplitude of each of its components.
  • The first figure on this page shows the spectrum of a simple wave (note that it has only one component). Click inside the box to hear the tone.
  • The second figure shows the spectrum of a complex wave. This sound has four components, represented by the lines in the spectrum. Click on each line to hear the corresponding component. Click inside the box (but not on one of the lines) to hear the complex tone.
  H. Timothy Bunnell, University of Delaware

• Demo #12: Computer-generated simulation of the glottal source (see also section (IV) below)
  This sound file is a simulation of what you would hear if you placed a microphone directly above the glottis during voicing.
  University of Delaware Speech Research tutorials

III. Basic acoustics (3): Standing waves and resonances

• Demo #9: Three different systems and their standing waves
  This demo shows the first five standing waves for three types of mathematically simple objects that are useful in understanding sound waves in the vocal tract.

  Another term for standing waves is resonances. The standing waves, or resonances, of an object like a string or a tube are precisely those waves of the correct size (=wavelength) to be compatible with the location of nodes (fixed points; zero displacement) and antinodes (points of maximum displacement) in the object. The fixed end of a string is a node. When we are looking at a pressure wave, the open end of a tube is also a node (because it interfaces with atmospheric pressure, which is zero by definition). The closed end of a tube is an antinode.

  • Demo #9a: Nodes at both ends
    This demo shows the first five resonances of a system with nodes at both ends (like a string that is fixed at both ends, or a tube that is open at both ends). The resonances of this kind of system are the whole-number multiples of the lowest or first resonance frequency.

    The vocal folds do not literally vibrate like a string, but mathematically speaking, vocal-fold vibration also has resonances at all whole-number multiples of the lowest resonance frequency.

  • Demo #9b: Antinodes at both ends
    This demo shows the first five resonances of a system with antinodes at both ends (like a tube that is closed at both ends). Mathematically, this case behaves exactly like #9a; the resonances are the whole-number multiples of the lowest resonance frequency.

  • Demo #9c: Node at one end, antinode at the other
    This demo shows the first five resonances of a system with a node at one end and an antinode at the other (like a tube that is open at one end and closed at the other — which is like the vocal tract when a schwa vowel is produced). This time, the resonances are the odd-numbered multiples (1st, 3rd, 5th,...) of the lowest resonance frequency.

    From the Zona Land section on waves

• Demo #10: Standing waves, reflection, and interference
  This animation shows how interference between two waves moving in opposite directions...
  • creates a standing wave, if the interfering waves are the same frequency, such as a resonance wave and its reflection [select Sinusoid 5, 6, or 7 on the drop-down menu]
  • or does not create a standing wave, if the interfering waves are not the same frequency [select Sinusoid 8 or 9 on the drop-down menu]

  From the Zona Land section on waves

• Demo #11: Standing sound waves
  This demo shows how air pressure waves in a tube actually relate to typical standing-wave diagrams.
  Dan Russell, Penn State University

IV. The source-filter model of speech production

• Demo #12: Computer-generated simulation of the glottal source
  This sound file is a simulation of what you would hear if you placed a microphone directly above the glottis during voicing.
  University of Delaware Speech Research tutorials

• Demo #13: Source and filter for schwa
  This page shows pictures of the vocal-tract filter function for schwa, the glottal source spectrum, and the combination of the two (which is the spectrum of a schwa).
  Kevin Russell, University of Manitoba

• Demo #14: Source and filter for [æ], [i], [u], [a]
  This page shows another glottal source spectrum, the vocal-tract filter function for [æ], and their combination (which is the spectrum for [æ]). There are links at the bottom of the page for three more vowels: you can view their spectra and their waveforms, and listen to the vowels.
  University of Delaware Speech Research tutorials

V. Modeling formant frequencies: Vowels

• Demo #15: Vocal tract model with duck-call source
  This demo uses a duck call (!) to simulate the glottal source in human vowel production. Plastic models of the vocal tract as it would be configured for [a i e o u] filter the duck-call source and produce vowels that are quite recognizable.
  From the Exploratorium web site, now via the Wayback Machine

• Demo #16: Helmholtz resonance
  Includes a helpful animation of a Helmholtz resonator and the resulting pressure-by-time graph.
  From the Music Acoustics site, University of New South Wales

• Demo #17: Simplified vowel synthesis (based on the Klatt speech synthesizer)
  This synthesizer lets you specify values for fundamental frequency and formant frequencies, and hear the resulting vowel quality.
  H. Timothy Bunnell, University of Delaware

• Demo #18: Use the "Vowel Editor" to synthesize vowels in Praat (PDF handout)

 

Additional information: More links for review and extra practice

• The following web sites are the sources for most of the demos listed above, and they all have much more information about acoustics and/or waves:
  • The waves section of the Zona Land Education math and science site, by Edward A. Zobel
  • Acoustics tutorials by H. Timothy Bunnell, University of Delaware
  • The Acoustics and Vibrations Animations page by Dan Russell, Penn State University

• Two tutorials from The Physics Classroom
  • Waves
  • Sound Waves and Music

• Examples of synthesized speech from a vinyl recording accompanying Klatt's (1987) paper on the history of text-to-speech conversion provided by the Phonetics Group at the University of Utrecht (click on the menu options on the left side)

• The Music Acoustics site, University of New South Wales