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Oscilloscopes: Seeing Sound

  • Introduction
  • Video & Results
  • Materials
  • Procedure
  • Preparation & Notes
  • Download Files

Introduction

In these activities, students will:cforkwave

  1. Use a computer software to observe sound waves from various sources.
  2. Establish connections between pitch and frequency.
  3. Establish the connection between volume and amplitude.
  4. Use their voice to modulate both frequency and amplitude of the sound waves they create.

The oscilloscope (oscope) is a commonly used laboratory piece of equipment that is used to observe electrical signals in real time. Scientists and engineers use them to test the performance of instrumentation by measuring voltage and frequency signals produced by the instrument. In this activity, the input for signal will be noises created by students. Computers and smart phones with downloaded software will be used as oscilloscopes, so that students can observe changes in frequency (pitch) and amplitude (volume) of sounds they create. The sounds will be converted into an electrical signal using the built-in microphone and will be displayed live on the computer or phone screen.

Demonstration of the tuning fork sound as viewed by SoundView

 

 

Video Using SoundView to identify frequency of tones on a keyboard

Materials

  • Oscilloscope type software to run on a PC, Mac or SmartPhone

    Mac OSX: SoundView (App Store, $1.99), Fftscope (Download, Free)
    PC:
    SmartPhone: Oscope (App Store, $4.99 iPhone)

  • Sources of tones to record and visualize
  • keyboard
    musical instruments
    voices
    dog whistle
    tuning fork (for students to try to sing)

Seeing Sound

  1. Open SoundView and expand "Waveform View" (top) and "Spectrum View" (bottom)to the full width of the computer monitor. Adjust the input gain to the high end of the sliding scale and adjust the x-axis on "Spectrum View" to range from 0 to 1 kHz.
  2. Use a cork on a pencil to strike a tuning fork, or strike the tuning fork on a shoe.
  3. Touch the tuning fork to a surface to amplify the tone. Holding the tuning fork on the computer near the speaker worked well.
  4. Observe the wave form in the top window and the peak frequencies in the lower window.
  5. Try different tuning forks and see if the increase or decrease in signal frequency in both windows.
  6. Repeat with musical instruments. Adjust the "Display Width" in the wave display and see how it affects what you see.

Hit that Note!

  1. Strike a tuning fork and hold it near your ear.
  2. Try to match the pitch coming from the tuning fork with your voice.
  3. Monitor with SoundView. How close do you get to the frequency?

Sounds Beyond our Ears.
Humans can hears sounds that range in frequency from 20 - 20,000 Hz. Dogs can hear up to 50,000 Hz, above the human hearing range.

  1. Make sure that the "Spectrum View" window shows frequency beyond the 20,000 Hz (20 kHz), try 50,000 Hz.
  2. Blow into the dog whistle and see if you can see the high frequency components of the dog whistle sound that are above the human range (>20 kHz).

 

Notes

Choice of software:
We have more experience with OSX. There may be more free software options available with Windows.

SoundView, installed on a MacBook Pro, for $1.99 at the App Store is easy to use but you cannot export the data. It displays both the time domain and the frequency domain simoultaneously. You cannot freeze the display and you can't measure the precise frequency of your sound. For dramatic display, pick SoundView.

Fftscope is free and relatively easy to use. I had difficulty getting the vertical scale to fill the screen during data collection. It does export numbers that can be plotted elsewhere. If you have more sophisticated participants and you'll want to plot and manipulate the data, Fftscope is the best choice.

References

  1. Seventh String Website with a table listing the frquencies of standard notes in the range of musical instruments.

Download files