Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!apple!agate!ucbvax!gnh-applesauce.cts.com!flee From: flee@gnh-applesauce.cts.com (FRANK LEE) Newsgroups: comp.sys.apple2 Subject: Re: Stuff and more stuff Message-ID: Date: 22 Jan 91 05:27:31 GMT Sender: daemon@ucbvax.BERKELEY.EDU Organization: The Internet Lines: 17 X-Unparsable-Date: Mon Jan 21 91 at 07:31:54 (EDT) About writing software in assembly to stretch a machine's abilities, you're right. In days long past, people were able to: achieve four-voice sound on an Apple II+/48k/1.023MHz through assembly alone! do advanced vector animation... etc.... About aliasing as it applies to A/D conversion, there's a rule in information theory (Nyquist Theorem) that your sampling rate must be GREATER than twice the highest frequency you intend to sample, else you'll get bad results. There are two ways of dealing with it. One is to use a low-pass filter with a cut-off at or slightly below 1/2 your sampling frequency. Another is to dither the audio with pink noise (i.e. noise whose intensity decreases as frequency increases). A construction article for just such a device appeared in Popular Elctronics, April 1990, that'll dither any analog input. INET: flee@gnh-applesauce.cts.com UUCP: crash!pnet01!gnh-applesauce!flee ARPA: crash!pnet01!gnh-applesauce!flee@nosc.mil