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From: ron@brl-tgr.ARPA (Ron Natalie )
Newsgroups: net.audio
Subject: Re: CD Reflections
Message-ID: <7441@brl-tgr.ARPA>
Date: Wed, 16-Jan-85 19:53:30 EST
Article-I.D.: brl-tgr.7441
Posted: Wed Jan 16 19:53:30 1985
Date-Received: Sun, 20-Jan-85 05:26:00 EST
References: <15100001@hpfcmp.UUCP> <3411@mit-eddie.UUCP> <1420@hplabs.UUCP>
Organization: Ballistic Research Lab
Lines: 20


> 
> It seems to me that the disc itself was created with a given sampling rate.
> How can a player change this?
> 
Sampling has a funny definition here.  They mean number of numbers output
by the DtoA per second.  The problem is that the D to A transits from one
number directly to another number.  This sharp transition generates all
kinds of higher frequencies which must be filtered out (as a result of this
44kHz square wave you've just created).  You have to be really careful with
your filter to get rid of the things that are a result of the transition
without mucking up the encoded signal.  So, lets interpolate and generate
three intermediate steps in between each of the original samples.  Now
the step transitions are generating 176 kHz squarewaves, and you can be
a little sloppier with your filter because rather than being 22kHz above
the real signal you are 154 kHz above it.  You are infact doing some of
the low pass filtering in the digital domain because it's easier (i.e.
cheaper) to build that way.

-Ron