Xref: utzoo sci.electronics:18212 comp.dsp:1338 Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!udel!burdvax!aviary!gaby From: gaby@Stars.Reston.Unisys.COM ( UNISYS) Newsgroups: sci.electronics,comp.dsp Subject: Re: A question about the Nyquist theorm Message-ID: <1180@aviary.Stars.Reston.Unisys.COM> Date: 5 Mar 91 13:31:13 GMT References: <20408@shlump.nac.dec.com> <625@ctycal.UUCP> <11515@pasteur.Berkeley.EDU> Reply-To: gaby@Stars.Reston.Unisys.COM (Jim Gaby - UNISYS) Organization: Unisys Corporation, Reston, VA Lines: 31 >jbuck@galileo.berkeley.edu (Joe Buck) writes: > > >Example of CD salespeak: pushing oversampling as an advanced technical >feature. Oversampling is simply inserting zeros between the digital >samples and thus increasing the sampling rate. It's used because then you >can use cheaper, less complex analog filters; it reduces the system cost. >Still, some sales critters think it's an advanced technical extra. I think the oversampling is not time interpolation (which by Nyquist does not add any more information to the originial signal), but more error correction oversampling. I.e. the same bit is sampled multiple times to determine its value. I assume that this is done by sampling over the duration (space on the CD) of the bit. Since the same bit value is sampled multiple times (eight in the case of 8 times over sampling) I assume some voting procedure is used to determine the "true" (or best estimate) of the bit value. I assume this results in less tracking and sample errors. For an ideal system, it also implies that if the CD had a higher density (say 8 times) the laser can read it at this resolution (i.e. you could put 8 time the music on one CD). I think it is a little generous to think that the industry truely does "oversampling" as it is implied by signal processing connotations. This (as you say) requires more compute requirements to ensure proper interpolation of the sampled data. If the interpolation (filtering) is done wrong, then the quality of the output would go down... - Jim Gaby gaby@rtc.reston.unisys.com