http://en.wikipedia.org/wiki/Modulation
http://www.tscm.com/modulate.pdf
http://en.wikibooks.org/wiki/Communication_Systems/What_is_Modulation%3F
http://en.wikipedia.org/wiki/Amplitude_modulation
http://en.wikibooks.org/wiki/Communication_Systems/Amplitude_Modulation
http://www.soundonsound.com/sos/mar00/articles/synthsecrets.htm
http://demonstrations.wolfram.com/AmplitudeModulation/
http://robotics.eecs.berkeley.edu/~sastry/ee20/modulation/node3.html
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/RadCom/part9/page1.html
https://ccrma.stanford.edu/~jos/st/Sinusoidal_Amplitude_Modulation_AM.html
http://itee.uq.edu.au/~coms3100/Lecture%20Notes/lec09.pdf
http://local.eleceng.uct.ac.za/courses/EEE3086F/labs/EEE3086F%20Introduction%20to%20Simulink.pdf