http://www3.nd.edu/~mhaenggi/ee344-04/overview.html

http://tintoretto.ucsd.edu/jorge/teaching/mae143a/lectures/5fourierseries.pdf

http://www.csie.nctu.edu.tw/~cmliu/Courses/audio/zfreqmap.pdf

http://course.ee.ust.hk/elec215/lecture/Chapter-5-Transient-and-Frequency-responses-of-LTI-systems.pdf

http://eeweb.poly.edu/~yao/EE3054/Ch10_freqRespCT.pdf

http://www.google.com/url?sa=t&rct=j&q=frequency%20response%20of%20continuous%20time%20system&source=web&cd=9&cad=rja&sqi=2&ved=0CGQQFjAI&url=http%3A%2F%2Fusers.ece.utexas.edu%2F~bevans%2Fcourses%2Fee313%2Flectures%2F23_Frequency_Response%2Flecture23.ppt&ei=XuPnUMbHD82Qswb1moGIAw&usg=AFQjCNG92hIDb_E-P5bfQ18puIf2HUi0_A

http://www.csee.wvu.edu/classes/ee327/resources/dt_freqresp.pdf

http://seit.unsw.adfa.edu.au/staff/sites/valu/TEACHING/SS/lect11-DT-filters.pdf

http://www.google.com/url?sa=t&rct=j&q=frequency%20response%20of%20discrete%20time%20system&source=web&cd=20&cad=rja&ved=0CGIQFjAJOAo&url=http%3A%2F%2Ffaculty.citadel.edu%2Fpotisuk%2Felec423%2Fppt%2Ffreq_res.ppt&ei=fuXnUN2-GOuN4gTMooDYDg&usg=AFQjCNHzJ2DtZIkT-ZkaqlVST8l0oqgjug

http://mmc36.informatik.uni-augsburg.de/mediawiki//images/4/47/WS0809_AIR_chap04_p4.pdf