Procedure

In this laboratory, you will analyze a variety of sound recordings. Each recording contains a single spoken word, featuring a single vowel sound. For each sound, you will use provided third-octave filter bank software to visualize the different sounds.

• If you have not already done so, install the program Octave on your computer. Start the program by typing octave on the command line. Also, download the archive of source code required for this lab, and uncompress the archive into the directory in which you will be running Octave.

• First, we need to load the first sound into Octave so that we can analyze it. To do this, enter the following command:

    > x1 = wavread('vowel1.wav');
  

• To listen to the recording you have just loaded, enter the following command:

    > play_sound(x1);
  

  Can you identify the vowel sound? To learn about the technical terminology used to describe various vowel sounds, visit the following online article: http://en.wikipedia.org/wiki/Vowel. What is the technical term and symbol for this vowel sound?

• Next you can plot a third-octave analysis of the vowel sound you just played by entering the following command:

    > third_octave_analysis(x1);
  

  On the plot, the $x$-axis shows the time in seconds, and the $y$-axis shows a third-octave band index $\ell$, where $\ell = k - 11$, where $k$ is defined as in Equation (3). In other words, $\ell = 11$ corresponds to a frequency of 1 kHz. The orange-red colors on the plot indicate areas of high energy, whereas the blue-dark colors on the plot indicate areas of low energy. Which frequency index $\ell$ shows approximately the darkest red patch in the middle of the recording?

• Now load a second recorded vowel sound (this is a different vowel than the first):

    > x2 = wavread('vowel2.wav');
  

  Again, you can play this second recording using the play_sound() command:

    > play_sound(x2);
  

  What is the technical term and symbol for this vowel?

• Finally, you can perform a third-octave analysis on this recording by issuing a familiar command:

    > third_octave_analysis(x2);
  

  In this plot, you should notice a different pattern of orange-red patches. How does this pattern differ from the previous pattern? Do you think you could tell the vowels apart by looking only at the pictures?³