Exercise 4

Please do the following and answer the questions:

1. Read in the audio file in /home/sigproc/sjreeves/matlab/learning/eeee.au using auread. (If you followed the instructions in Exercise 1, you should be able to do ee = auread('eeee.au');. This is an audio file of Dr. Reeves saying "eeeee". (If your computer has audio capability, you can listen to the sound with sound. Plot the first 1000 point or so to get an idea of the shape of the signal. What is the approximate period of the signal in samples and in seconds? (The signal is sampled at 8 kHz.)

2. Compute the autocorrelation of ee by computing the cross-correlation of ee with itself using xcorr(). Plot the resulting vector beginning with the mid-point (the origin) up through 1000 points to the right:

   ree = xcorr(ee,ee);
   plot(ree(31422/2+[1:1000]))
   

   Explain how the characteristics of this plot can be explained by the properties of autocorrelations of functions with period components. Can you identify the period from the autocorrelation plot?

3. Find the spectral density of ee using spectrum(). To plot, do the following:

   [spectee,f] = spectrum(ee,ee);
   semilogy(f/2,spectee(:,1))
   

   The frequencies are labeled in cycles per sample. Can you figure out the fundamental frequency (and period from the plot)?

4. As you can see, the phoneme (unit of speech) "eeee" has a very distinct spectral shape. Read in the file 'ohhhh.au' and compare the spectrum, the waveform, and the autocorrelation. Describe any clear differences.

5. Suggest another exercise that would help you understand this material better.