Path: utzoo!attcan!uunet!husc6!bbn!mit-eddie!uw-beaver!tektronix!tekcrl!tekfdi!videovax!stever From: stever@videovax.Tek.COM (Steven E. Rice) Newsgroups: comp.sys.amiga Subject: Re: Sampling at 29KHz (long) Message-ID: <5019@videovax.Tek.COM> Date: 25 May 88 14:24:15 GMT References: <2845@polya.STANFORD.EDU> <734@eos.UUCP> <53788@sun.uucp> <5637@cup.portal.com> <3854@cbmvax.UUCP> Reply-To: stever@videovax.Tek.COM (Steven E. Rice, P.E.) Organization: Tektronix Television Systems, Beaverton, Oregon Lines: 43 In article <3854@cbmvax.UUCP>, Joe Augenbraun (augi@cbmvax.UUCP) asked how a digital system would reconstruct the original signal when the sampling rate was not very much higher than that required to give two samples per cycle of the signal. He included some diagrams of an 18 kHz signal sampled at 44 kHz. He conjectured that the D/A converter would recreate the signal as follows: > > . . > |. . .| . > | . . . . | . . | . > | . . | | . | . > | . . | | . . | . > | . . | | . . | . > | | | | | | | (ref) ----------------------------------------------------------------------- Ignoring overshoots, ringing, and so forth (and assuming negligible risetimes) the reconstructed output would actually look like this: .----------. .----------. | | .----------. | | | | .----------' | | | | | | | | | | | | | | | | |__________| |----------| |_ | (ref) ----------------------------------------------------------------------- This then goes to a "reconstruction filter" (which is just a low-pass filter), to remove the high-frequency harmonics, leaving a faithful reproduction of the original signal. (There is more to it. Email if you are interested in the gory details.) Steve Rice ----------------------------------------------------------------------------- * Every knee shall bow, and every tongue confess that Jesus Christ is Lord! * new: stever@videovax.tv.Tek.com [phone (503) 627-1320] old: {decvax | hplabs | ihnp4 | uw-beaver}!tektronix!videovax!stever