How can we describe sounds?

Write down what you know about sound. Consider these questions.

• Sound is vibrations. What vibrates?
• Sound can be transmitted through the air and through solids. How does it travel from one place to another?
• If you were near an explosion in outer space, would you hear it?

Since you can’t see sounds, one way to explore them is to display and observe the sound vibrations on a graph. When something vibrates, it moves back and forth in a regular way, often so fast that you need a computer’s help to see the pattern. This is what you will observe in this investigation.

• microphone
• Sound Grapher. If you do not have the Sound Grapher on your desktop, go to this link and download the Sound Grapher.

This activity addresses NSES standards for physical science (for transfer of energy) and inquiry at grades 5-8
(http://books.nap.edu/readingroom/books/nses/6d.html#ps).

Do not make loud noises close to other people’s ears. Eardrum damage may result.

1. Make sure your computer has either a plug-in or a built-in microphone. Refer to Technical Hints to connect the microphone.
2. Turn up the input volume for the microphone.
3. Start the Sound Grapher. Refer to this link to download the Sound Grapher. It will open in a separate window.
4. The Sound Grapher shows two graphs. Click on the graph you want to use. Click the Start button to start the Sound Grapher.
5. As you make noise, wavy lines should appear on the screen. When you click the Stop button, the graph “freezes” the sound picture at that moment. Here is an example:
6. You can then switch to the other graph to look at another sound. The space bar and the Return key also run Start/Stop functions.
7. A single frequency appears as a simple sine wave. When more than one frequency is present in the sound, the waveform is a combination of several sine waves and looks more complex. It is difficult to tell what is happening from the waveform alone, so an additional analysis tool is provided. Click the “Waves” button, and change the drop-down menu to “Frequencies.” The screen now displays the distribution of frequencies that are present in the sound, with frequency plotted on the x-axis. Here is an example:
   

Here are four different sounds. Click on each one to play it. Listen carefully. You can probably tell what they are. If these links don’t work, close your eyes while your teacher makes different sounds for you to discuss.

For each sound, write down what you think made the sound. Also write a description of the four different sounds. Use words like loud, soft, harsh, gentle, squishy, sharp, buzzy, etc. Be prepared to share your results with the class.

• play sound 1
• play sound 2
• play sound 3
• play sound 4

1. Try out the Sound Grapher for 5 minutes. Make as many different kinds of sounds with your voice as you can — loud and soft, high and low, different vowels, mouth open and closed. The sounds need to be steady so that you can see their pattern. Click the Stop button to study each sound. Think about how it looks in the graph. Then try another sound.
2. Click on the top graph of the Sound Grapher. Refer to Technical Hints to use the Sound Grapher. Make one long uuu sound (as in the word "moo"). Keep the picture of the sound by clicking the Stop button.
3. Observe the graph. The bumps are a record of sound vibrations. In this case, your vocal cords vibrate and make the air vibrate as well. The patterns travel through the air as variations in air pressure and make the microphone in your computer vibrate. It then displays the pattern.
4. Look for a pattern in the graph that repeats again and again. This is a picture of the “uuu” sound you are making.
5. Use words to describe the pattern that repeats. Also record how many times the pattern appears on the graph. Make a drawing that shows the pattern that repeats.
6. Now click in the bottom graph of the Sound Grapher. Make a “hissing” sound (shshsh as in "shush"). Keep the picture of the sound by clicking the Stop button.
7. Observe the graph. This is a picture of a hissing sound. Look for a pattern that repeats in this sound. Can you find one? Does it repeat? Make a drawing that shows the pattern.
8. Using the upper and lower graphs, compare the two sounds “aaa” and “eee” made by the same person at the same pitch and loudness. That is, change the vowel but nothing else. How is the pattern of these two sounds different?
9. Try other vowels. Draw each pattern and describe what is unique about it.
10. Using the upper and lower graphs, pick a vowel and have two different people record the same vowel, again at the same pitch and loudness. Can you see a difference between the two patterns?
11. Repeat these comparisons using the “Frequencies” mode instead of the “Waves” mode. You will notice that each type of sound has several frequency spikes in it, meaning that it is mixture of these frequencies. Write down the mixture of frequencies in the different vowels. Compare two people saying the same vowel.

1. Compare the two sounds you recorded in the top and bottom graphs of the Sound Grapher (uuuu…as in “moo” and shshsh as in "shush"). How are they the same and how are they different? Why do you think they don’t look the same?
2. Does each vowel have a “signature” shape that makes it different from the others? Can you recognize this signature in both the “waves” mode and the “frequency” mode?

Play each sound and try to match it with one of the following patterns.

• Sound A
• Sound B
• Sound C
• Sound D

Pattern 1:

Pattern 2:

Pattern 3:

Pattern 4:

Look at non-human sounds — anything you have at hand. See if you can predict or explain what a given sound will look like, compared to what it sounds like.