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Path: utzoo!watmath!clyde!burl!ulysses!mhuxj!ihnp4!inuxc!pur-ee!uiucdcsb!emrath
From: emrath@uiucdcsb.UUCP
Newsgroups: net.audio
Subject: Re: Sheffield CDs and why they sound bad
Message-ID: <5700063@uiucdcsb.UUCP>
Date: Fri, 12-Oct-84 04:26:00 EDT
Article-I.D.: uiucdcsb.5700063
Posted: Fri Oct 12 04:26:00 1984
Date-Received: Sun, 14-Oct-84 07:03:52 EDT
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Nf-ID: #R:watdcsu:-46000:uiucdcsb:5700063:000:1625
Nf-From: uiucdcsb!emrath    Oct 12 03:26:00 1984

Regarding Shaun's point about compression:
It sounds like what you are saying is that a CD could be made
where the data is 16 bit samples, but every so often a control sample
is read which (digitally) controls the gain of the analog (de)amplifier
used on the output of a 16-bit D/A.  Assuming you could make the
original recording using a 20 or 24 bit A/D (maybe someday), the
samples could be converted to 16 bits by shifting small ones left
and setting the control words to decrease the gain of the playback
amplifier by 6dB for each bit the following samples are left shifted.
Naturally, the 20 -> 16 bit conversion looks ahead to make sure that
no MSBs are lost, only the LSBs of numerically large samples.
The recorded signal is compressed, and proper playback entails downward
expansion.  It would probably sound bad without proper playback.
One possible problem with this may be the inability to switch the
gain of the PB amp fast enough and at the exact times, thus causing
distortion and noise.  (also, as you pointed out, its of dubious value)

Any way, the whole idea raises the following question.
Do current CDs have data format version information stored
on the disk, allowing future format changes?    (they must, I suspect)
A drastic change, such as the one above, might mean that version n
players would reject version n+1 disks, but a version n+1
player should be able to play any disk of version 1..n+1.
Recalls the evolution of the cassette, with CrO2, Dolby B,
Dolby C, dbx, Metal....

Perry Emrath	...pur-ee!uiucdcs!emrath
DCS, U of IL	emrath%uiuc@csnet-relay.arpa

	"Life is a bitch, and then you die"