stanford, 2
ref
SA
chapter 33 from The Scientist & Engineer’s Guide to Digital Signal Processing
dspcan
http://www.emba.uvm.edu/~gmirchan/classes/EE275/Handouts_Ed4/Ch06(4e)Handouts/Ch6(1)Handouts_4e.pdf
http://www.emba.uvm.edu/~gmirchan/classes/EE275/Handouts_Ed4/Ch06(4e)Handouts/Ch6(2)Handouts_4e.pdf
matlab
https://www.math.uci.edu/icamp/courses/math77a/lecture_10f/rational_filters.pdf
single pole filter frequency response
https://ccrma.stanford.edu/~jos/fp/Elementary_Filter_Sections.html
https://ccrma.stanford.edu/~jos/filters/filters.html
see https://ccrma.stanford.edu/~jos/filters/Stability_Revisited.html
http://fourier.eng.hmc.edu/e102/lectures/Z_Transform/node2.html
http://www.eecg.toronto.edu/~ahouse/mirror/engi7824/course_notes_7824_part6.pdf
https://en.wikipedia.org/wiki/Linear_time-invariant_theory
http://pilot.cnxproject.org/content/collection/col10064/latest