I am new to the Kiwi so I hope this page isn't a repeat of something that's already been posted. The site comes from John Hopkins University and was shown to me by my ECE202 instructor, Babak Ziaie. The part that has been most helpful to me is under the first link 'Joy of Convolution.' I haven't even had time to get around the whole site, but there seem to be other links on it that may be helpful to reference. Enjoy.
