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From: wjm@lcuxc.UUCP (B. Mitchell)
Newsgroups: net.audio
Subject: Re: CD Oversampling
Message-ID: <336@lcuxc.UUCP>
Date: Sun, 24-Mar-85 21:02:15 EST
Article-I.D.: lcuxc.336
Posted: Sun Mar 24 21:02:15 1985
Date-Received: Mon, 25-Mar-85 03:55:49 EST
Organization: Bell Communications Research, Inc.
Lines: 14

The advantage to oversampling in CD players is that it simplifies the design
of the low pass analog filters that follow the D/A converter.  These filters
are required to prevent aliasing - that is frequencies > 22.05 kHz created
through the digital sampling process causing spurious signals in the analog
output.  Without oversampling, a VERY sharp cut-off at 22.05 kHz is required
and such "brick wall" filters, have rather nasty phase responses.  With
oversampling a filter with a much more gentle roll off can be used since
the oversampled D/A output will not contain spurious signals below 88.2
kHz.  (The spurious signals only occur at frequencies greater than half
the effective digital sampling rate - 44.1 kHz without oversampling,
176.4 kHz with it).
Regards,
Bill Mitchell (ihnp4!lcuxc!wjm)