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From: ark@alice.UucP (Andrew Koenig)
Newsgroups: net.analog
Subject: Re: Oversampling in CD players
Message-ID: <5352@alice.uUCp>
Date: Sun, 27-Apr-86 12:32:36 EDT
Article-I.D.: alice.5352
Posted: Sun Apr 27 12:32:36 1986
Date-Received: Tue, 6-May-86 04:45:31 EDT
References: <241@ur-tut.UUCP>
Organization: Bell Labs, Murray Hill
Lines: 22

Oversampling refers to a process wherein each 16-bit sample is
converted to 2**k (16-k)-bit samples.  In players made by
Philips or using their chip set, k=2.  The idea is this:
each 16-bit sample has the two low-order bits stripped off
and saved, giving a 14-bit sample.  Each 14-bit sample is
followed by three additional samples, all of whose bits are 0.
These samples, along with the discarded bits, are fed into a
DIGITAL filter.  That is: the filter works by manipulating the
bits, not the analog signal.  The output of the filter goes
into a 14-bit D-A converter, then into an analog filter.

The advantage lf all this is that the analog filter does not
need to have the sharp cutoff associated with systems that
do not oversample.  It is thus much easier to build.  Also,
it is possible to make digital filters that exhibit better
phase response than practical analog filters.

That's the theory, anyway.  I should mention, for completeness,
that a bunch of us have compared CD players with and without
oversampling, using carefully level-matched, double-blind
listening tests, and none of us could reliably hear the
difference.