You've probably seen one before in relation to music. However, since we're dealing with computer-generated tones here, the spectrogram looks very very sparse (few overtones). You can see patterns in music as well, just not as clearly (because there's a lot more going on).
If you'd like to make your own, consider looking into GNU Octave (http://www.gnu.org/software/octave/) or possibly Scilab, both of which are free.
EDIT: I might add that Audacity can easily view the spectogram of a sound file, but if you want to manipulate the signal programatically (filters and so on; signal processing is a great subject), try the above.
You've probably seen one before in relation to music. However, since we're dealing with computer-generated tones here, the spectrogram looks very very sparse (few overtones). You can see patterns in music as well, just not as clearly (because there's a lot more going on).
If you'd like to make your own, consider looking into GNU Octave (http://www.gnu.org/software/octave/) or possibly Scilab, both of which are free.
EDIT: I might add that Audacity can easily view the spectogram of a sound file, but if you want to manipulate the signal programatically (filters and so on; signal processing is a great subject), try the above.