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Conference cookie::notes$archive:cd_v1

Title:	Welcome to the CD Notes Conference
Notice:	Welcome to COOKIE
Moderator:	COOKIE::ROLLOW

Created:	Mon Feb 17 1986
Last Modified:	Fri Mar 03 1989
Last Successful Update:	Fri Jun 06 1997
Number of topics:	1517
Total number of notes:	13349

5.0. "Anyone heard CD Dropout?" by GOLD::WEAVER () Sat Dec 17 1983 11:03

From:	DVINCI::CREASER      "Gerald Van Creaser"   16-DEC-1983 10:50
To:	GOLD::WEAVER

Some CD listening observations

I have finally heard the results of the long awaited Ultimate audio
reproduction system. My reaction is Great, but it seems we're not
quite there yet. The basis for this mixed review is primarily due to
what I'll call "Drop-out".

To date I've listened to three different manufacturer's units and
observed the Drop-out effect on all three. At the first session, the
clerk was unable to suggest any causes, however I was able to identify
one cause for sure and can suggest some others. This particular demo
was on a Phase Linear CD which has good selection controls and a track
timer. The Drop-outs were repeatable and when the disk was examined it
was obvious that surface damage in the form of scratchs, foreign particles
and etched fingerprints were a major suspect. I was relieved to known
the my usual care for quality analog disks would resolve this problem.

Next I asked if a previously unused disk (and digitally mastered, not
remastered) could be used. We located a good one, but alas the Drop-outs
continued although at a vastly reduced rate. They were not always
repeatable which leads me to believe that it is related to read error
rates in the circuits rather then media problems, but there is no
clear separation of causes here...could be a combined effect.

Finally,  I've listened at other distributers to a Marantz and Magnovox
seeking to determine if my experience was isolated (the Phase Linear
may have been mistracking, etc.). Drop-outs were detected on both units.
In all fairness the single Drop-out heard on the Marantz unit was not
repeatable and nearly 30 minutes of intense listening failed to produce
more.

I am very interested to hear if others have noted the effect. The Drop-outs
have a duration of about 1/10 to 1/4 sec. and occurred on an average at
5 minute intervals.

Jerry Creaser

T.R	Title	User	Date	Lines
5.1		GOLD::WEAVER	`Sat Dec 17 1983 11:27`	22
	That's interesting, I don't recall ever hearing any dropouts except for two instances: The first was at Lechmere when they had the Fisher unit set up for demoing and I was listening to a CD that looked like it had been handled by the American Tourister Guerrilla. The disc also got in a "repeat groove" so it couldn't get past one spot on the disc. The second was a CD I had bought at Rock'n Mania, Frida's "Somethin's Going On". The last song on the disc had a very repeatable muted effect throughout. Close examination of the disc revealed what appeared to be bubbles caught in the substrate over the last selection. I simply returned the disc and the new one was fine. Note that both of those mutings were quite repeatable, and the causes were known (in the case of the repeating disc at Lechmere, a concentric scratch was the cause). Note that I own a Sony CDP-101 and I have over 40 titles ranging from classical to rock. -Dave
5.2		MUN02::ORA	`Mon Dec 19 1983 11:16`	8
	The HiFi press here has tested practically all the available CD players by now, and I haven't heard (or read) of any problems with dropouts with discs in reasonable shape. Most of them use the Philips test disc which icludes round black spots of certain diameters. There are certainly huge differences in error correction capabilities; there's quite a lot of variation in the diameter of the "black hole" required to cause audible effects on a certain player.
5.3		AMBER::KAEPPLEIN	`Fri Jan 13 1984 15:50`	8
	Dropouts are due to read errors caused by bad media or laser mis-tracking (usually caused by vibration or jarring). Record companies mass-produce CDs just like records and some CDs are probably better than others, just like analog records. The difference is that turntables don't come with click and pop boxes, but CDs do in the form of circuits which try to average and guess data.
5.4		NEWTON::GWB	`Mon Jan 16 1984 16:14`	29
	I have had two disks that gave me problems with dropouts. I took these back and had them replaced. The replacements were fine. I have noted small bubbles in the plastic coating on the disks, but it is difficult to correlate these with any particular problem since bubbles in the plastic seem to be occur on all of the disks. This is probably a feature of the process used to coat the disks. I have read somewhere that raw error rate of a disk as defined by the standard will be one packet in 10^3 requiring correction. The ECC correction will fix all but about 1 packet in 10^8. CD players are also sensitive to vibration to an extent (vibration sensitivity varies from maker to maker, just as it does with turntables). The laser beam has to be focused precisely on the surface of the disk (within a few microns) to read the data and obviously a sudden movement of the player can disturb that focus generating some number of unreadable packets until the laser refocuses itself. (By the way, I find the magic servo system that keeps the laser focused and the data rate constant while varying the speed with which the disk rotates the most incredible thing about the digital disk player; 16-bit D to A converters and "on the fly" ECC decoders are rather trivial by comparison). I don't have any problems with vibration with the Sony CD-101, but then there is no reason to expect that I would at home. I suppose in a store with people milling around the unit might be subject to enough vibration to cause it to skip every now and then. Regards, George
5.5		PIXEL::DICKSON	`Fri Feb 03 1984 10:51`	11
	I heard the demo unit at Lechmere. Awful. Reviews I have read show considerable variation is error-recovery ability of different players. Smudges or vibration can sometimes be handled, but both together are too much. Note that the fragile side of a CD disk is the LABEL side, not the shiny side. I wonder what stores do with returned bad disks? Sell them to the next poor fool?
5.6		MUN02::ORA	`Mon Feb 06 1984 09:47`	18
	There really seems to be big differences in the error correction capabilities. The magazines here use the Philip test disk. It has black dots of up to 800 um (micrometer) in diameter on the "playable" side of the disk, a black stripe up to 900 um width on the "pit" side of the disk and "simulated" fingerprints (how do you simulate them?) Anyway, many players do not have any difficulties with this disk. The good ones in this respect seem to be all players manufactured by Philips (Philips, Marantz, Grundig), Technichs SL-P7 & SL-P8, Hitachi DA-800 (this is not a complete list). The bad ones start having dropouts at 300 um (0.3 mm) which isn't very much dirt... so better not scratch your disks and keep them clean!! I think none of the players has yet failed in the simulated fingerprint test. Some of the magazines also test the sensitivity to shock and vibration. There are great differences here, too, but for normal home use they all should be ok (could be a problem with car CD players!!!). Just keep in mind most of the players are not much better in this respect than good analog turntables.