The Science of Musical Instruments

     Singing and speech is created in an organ located in the neck called the larynx. The sound is produced by first drawing air from the lungs into the trachea. When this air passes through the larynx it causes the vocal cords (vocal folds) to vibrate which produces sound. The different pitchs of these sounds are controled by the various muscles surrounding the larynx. These muscles control the pitch of the sound by ajusting the tension and position of the vocal cords. By ajusting the tension or in othe words changing how loose the vocal cords are when the muscles tighten the vocal cords this produses a faster vibration of the cords which in turn creats a higher frequency which means a higher pitch. As you would expect loosing the cords would make a lower frequency therefore a lower pitch. When I say changing the position of the vocal cords I mean changing the length of the tube the sound energy travels through. The Stylopharyngeus muscle pulles on a bone that shortens the tube by doing this you create a higher pitched sound. The Infrahyoid muscels are responsible for pulling the larynx down lengthening the tube making a lower pithched sound. With a combanation of all these factors we are able to create the various noises used to sing. (adapted from http://home.comcast.net/~wnor/lesson11.htm)

 A whistle is created by controling a stream of air which is done by making a small hole with the lips then blowing air through the hole. When air passes by the the teeth the tongue and the lips the stream of air is altered which can produce vibrations of the and those virbrations or souds get louder in the mouth then that sound exits the mouth as what we can hear as whistling. Just as in singing the pitch of the whistle is controled by changing the things that produce it. The main thing people do to change the pitch of the whistle is by changing the position of the tongue. By moving the tongue you change how air moves over the tongue in turn creating different vibrations, which changes the sound. Also pitch can be altered by the way you make the hole with your lips. (http://en.wikipedia.org/wiki/Whistling) 

For a simulation click the link: http://phet.colorado.edu/simulations/sims.php?sim=Sound                                                
 

To see whistling at the highest level watch this video of the world championship of whistlin.