Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!sdd.hp.com!hplabs!hpfcso!hpfcdj!myers From: myers@hpfcdj.HP.COM (Bob Myers) Newsgroups: sci.electronics Subject: Re: A question about the Nyquist theorm Message-ID: <17660153@hpfcdj.HP.COM> Date: 22 Feb 91 21:26:02 GMT References: <91046.095459F0O@psuvm.psu.edu> Organization: Hewlett Packard -- Fort Collins, CO Lines: 18 >It appears that what I'll get is an am modulated signal that is some >combination of the 20khz signal and the 44khz sample rate. Yup, that's what you'll get, all right. But now run through the math that describes how to make this "AM signal," and you'll find that one of the components you'll get out of all this is a 20 kHz signal at (or at least in proportion to) the original amplitude, plus some other stuff that will be above the cutoff of the required LP filter (assume a "brick wall" at 22 kHz if you like). You CAN recover the original. Sampling theory is not always (some would say "never") intuitive. But the math does describe what we should expect out of it, and agrees with what you'll find in the "real world" pretty well when you go to try it. Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other myers@fc.hp.com | sentient life-form on this planet. Brought to you by Super Global Mega Corp .com