| Go to the LIBRARY.
They have BOOKS. They're kind of like essays and/or websites, but written by people who know what they're talking about. They collect all the good information in one place. Clearly you were expected to do some research on this, and teachers are WAY more impressed if you cite a couple of books, rather than websites.
To avoid plagiarism get a couple of books, either draw your own diagrams or STATE WHERE THEY CAME FROM EXPLICITLY, and cite the books at the end of your essay. A good piece of advice is never too write with the book open or a web page on screen, then you can't copy section verbatim, or even closely adapt. Always cite, and write in your own words.
For an essay like this you should avoid the big long block of text approach - that's fine for "what I did at the weekend", but you need to break it down. D/A's, sample rate, bit depth, compression, effects, A/D's etc Each organised into sections and subsections. Write out your section headings FIRST, and get them all in order and making sense. Then just fill in the text later.
Lot of diagrams...
Here's a bone for you:
@article{nyquist,
Author = {Harry Nyyquist},
Journal = {Trans. AIEE},
Month = {April},
Pages = {617--644},
Title = {Certain topics in telegraph transmission theory},
Volume = {47},
Year = {1928}}
Bung that in your bibliography...
Ian | 
