http://www.ece.jhu.edu/~cooper/courses/214/signalsandsystemsnotes.pdf

https://ccrma.stanford.edu/~jos/log/

http://abut.sdsu.edu/TE302/Chap4.pdf

http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT-KANPUR/Digi_Sign_Pro/pdf/final-chap-5.pdf

http://www.google.com/url?sa=t&rct=j&q=dtft+examples&source=web&cd=13&cad=rja&ved=0CDsQFjACOAo&url=http%3A%2F%2Fwww.sonoma.edu%2Fusers%2Ff%2Ffarahman%2Fsonoma%2Fcourses%2Fes400%2Flectures%2Fsigsys_lec_ch_12.ppt&ei=TrHnUJGFJoqi4gT6zIC4Ag&usg=AFQjCNGN_wX0pK2d6tD3RPd2lW-uUotNPg&bvm=bv.1355534169,d.Yms