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From: csdf%mit-vax@mit-vax.UUCP
Newsgroups: net.analog
Subject: Re: Oversampling in CD players
Message-ID: <285@mit-vax>
Date: Mon, 28-Apr-86 00:29:00 EDT
Article-I.D.: mit-vax.285
Posted: Mon Apr 28 00:29:00 1986
Date-Received: Sun, 11-May-86 15:43:56 EDT
References: <241@ur-tut>
Lines: 32

In article <241@ur-tut.UUCP> jgro@ur-tut.UUCP (Jeremy Grodberg) writes:
>   Everyone talks about the wonders of oversampling in their CD players, but
>I have yet to hear as coherent explanation of what oversampling actually is.

In order to sample audio data, one bandlimits it to 20KHz (you can't
hear above that) and samples it at 40KHz or more. 40KHz is the "Nyquist"
sampling rate and is the (mathmatically) theoretical sampling rate to
insure that all of the information in the signal is preserved. If you
OVERSAMPLE you get more information than you need.

>I have heard that it is a method of error correction, a method of insuring
>that the buffer to the A/D doesn't run dry during misreads, and a number of
>other seemingly absurd ideas.

These ideas are not absurd. Say you sample at 80KHz. That means that if
you have to, you can "zero out" every other sample and still have a
clean signal (if the output is properly filtered to 20KHz).

>My best guess is that it refers to the
>process of interpolating data points between the recorded data, providing
>a higher effective pseudo-sampling rate, thus allowing for reconstruction
>filter with much higher cut-offs, smoother roll-offs, and therfore greatly
>reduced phase shifts at audio frequencies.

Every now and then, sombody comes up with some sort of interpolation
scheme. These invariably warp the spectrum and therefore don't work. The
point of oversampling is that you have "data to burn" so you can afford
to miss a few samples here and there.

-- 
From the land of Chaldea.
-Charles