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What Does Sound Look Like? Oscilloscope Wave Forms.

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Author: Jerry Silver

The Idea

What does your voiceprint look like? You cannot see sound. But you can change the sound waves into electrical signals that can be displayed on a screen. Just as you found ways to visualize motion and to represent motion using various graphs, in this section you develop techniques to visually represent waves. This can enable you to study basic wave properties and to observe how waves combine to form new patterns.

You can go about this in two ways. One way is to use an oscilloscope, which is an instrument that takes an electrical signal and displays it in graphical form. Recently, a much lower cost alternative has become available that makes it possible to turn a computer into an oscilloscope.

This project focuses on how either type of oscilloscope can be used to study the wave properties of sound.

What You Need

  • oscilloscopes, which range in cost from just under $600 to thousands of dollars
  • sound card oscilloscope. You can turn your computer into a oscilloscope in several ways:
    • PC sound card distributed for private and noncommercial use in educational institutions at www.zeinitz.de/Christian/Scope_en.html. (Oscilloscope images shown in this and other sections are based on this sound card oscilloscope and appear courtesy of C. Zeinitz.)
    • Zelscope is available for a small charge at www.zelscope.com (this used to be called Winscope).
  • tuning fork
  • adapters
    • To connect microphone to computer. Microphones are either high- or lowimpedance connections and the computer input is typically a mini.
    • Microphone output to oscilloscope input (typically BNC connector).
    • Depending specifically on what connections you need to make, you can most likely find connectors at Radio Shack or build the connector you need.
    • Caution: Sound card oscilloscopes can handle only low-voltage inputs, such as from microphones. Attempting to use a sound card oscilloscope for larger electrical signal may damage your sound card. A reference for how to assemble a high-impedance circuit that can enable using a sound card oscilloscope for higher voltages is given in Project 115.
  • wave generator
    • stand-alone device designed for this purpose
    • keyboard with appropriate connectors
    • waveform generator available with some computer oscilloscopes

Method

Setting up the oscilloscope

  1. Connect the microphone to the oscilloscope input.
  2. Collect a test signal, such as your voice or a musical sound.
  3. Adjust the vertical scale, so the entire wave is displayed.
  4. Adjust the horizontal (time) scale, so the wave is displayed.
  5. If necessary, adjust the trigger to enable the wave to be properly displayed. (Chose continuous rather than single-event settings for the trigger.)

Displaying waves

  1. Generate a pitch audibly with a tuning fork, a keyboard synthesizer, or by a waveform generator. (Depending on your setup, you can use the waveform generator to produce an audible signal through a loudspeaker or send it directly into the input of the oscilloscope.)
  2. Increase the pitch (frequency) and compare to the previous shape.
  3. Decrease the pitch and compare to the previous measurements.
  4. Increase the volume (amplitude) of the sound and observe how the wave changes.
  5. Try your voice using the microphone. How does that compare to a pure tone, such as produced by the tuning fork?
  6. Observe different waveform shapes, such as sinusoidal, triangular, square wave, and sawtooth. How do they sound? What musical instruments do each of the previous waveforms most closely resemble?
  7. Play various musical instruments and identify fundamental waveforms that appear to be present in the instruments' waveforms.
  8. Just for fun: Observe various samples of music. Can you distinguish various musical styles just by looking at the waveform?
  9. Can you recognize the "voice signature" of different people as crime labs do all the time on TV?
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