Why CDs skip.

Cecil's Columns/Staff Reports
1

Although Cecil was correct in briefly explaining the reason for a CD to skip like an LP he did not complete the explanation. Why a CD SOUNDS like a record skipping is due to a feature called oversampling.
Without getting into the technical jargon of digital information systems, basically what it means is that the CD player will read a digital symbol several times (as many times as the oversampler dictates) and then verifies the most recent values it has received by calculating the average value that will produce the required sound.
When a scratch, dust, etc. is encountered, garbage values are entered into the calculations. If the CD player cannot distinguish what it is to produce, the process is repeated which causes the preceding sounds to echo until the CD players processor can come up with an acceptable value.
Sometimes it may take one, several, or an infinite number of repetitions for the CD player to proceed depending on the obstruction or damage to the information it receives.

2

<beating Jill>

http://www.straightdope.com/classics/a940304b.html

Now, if only Jill will show me how to do that so a new window pops up with the link… <wistful look in eyes>

3

I got a new window. Don’t you?

-Ryan
" ‘Ideas on Earth were badges of friendship or enmity. Their content did not matter.’ " -Kurt Vonnegut, * Breakfast of Champions *

4

Yikes!!! Demons inhabiting the computer all of a sudden! New windows without any added code!!! Famine and pestilence!!!

<Dammit, Ryan, I was hoping to lure Jill into a cyber discussion that might include the ass-kissing aspect she alluded to in another thread… ;)>

5

Actually, I have had two CD players have skipping problems that had nothing to do with the CD’s being played. (Though they seemed to skip more on Amy Grant CD’s, go figure.)

It turned out that the little gear that moves the laser/detector back and forth was worn and allowed too much “play.” The player was evidently losing track of its track. I fixed one by opening it up and adjusting a screw on the end of the gear that drove the lens/detector, tightening it up and removing the “backlash.”

Getting back to the Amy CD’s, I believe that the hole was slightly off center which made it lose the track a little more easily

6

I think your CD player just has good taste.

Now then. I have a copy of “Automatic for the People” by REM which has a big dent in it. It looks like the CD was pressed against the corner of a table or something. Thus, about 15 seconds into the sixth track (that New Orleans instrumental thing), the player\starts to skip. However, it does not repeat the same few note again and again; instead, it plays only about 1/2 the notes. I hear maybe 1/2 a second of music, then 1/2 a second of silence. But the truly strange thing about this is that it does not only occur for that one song. This bizarre intermittent playing will continue for the rest of the disc (the upside, of course, being that if I ever want to hear a remix of “Nightswimming,” I can) unless I skip the player ahead at least one track. Any ideas as to why this happens?

7

CDs skip on account of the difference in tension over the water surface and the gravitational pull. You hold the CD horizontally, crook your index finger and thumb around the curve, and toss it flat, with a slight twist of the wrist, towards the water. It will skip two or three times over the surface of the water before it sinks.

Before CDs were invented, we used to use flat round rocks for the same purpose.

… Eh? What? … Oh. Um. Sorry.

8

After about a year some of my new CDs started skipping. I returned them etc. Then my old CDs started skipping. I came to realize if I turn off my Anti Skip protection they didn’t skip. Odd but only some CDs skip with it on. Most play with it on. I guess some are more sensitive than others.

9

I can offer some insight into this: turning on the anti-skip circuit causes the CD to turn at a much higher speed. This allows the player to “read ahead” the CD and store x seconds (where x is between 3 and 40) of music you haven’t yet listened to (if your CD player has a window where you can see the disc turning, you’ll see it speed up when you turn on the skip protection).

Oviously, the faster the disc is turning, the less time the laser has to read each pit in the CD. If the laser is getting out of alignment (common in portable players where they’re constantly getting bounced around) or its power is diminishing (possible, but less likely, especially if your player is only a couple of years old) this is likely what’s happening. It doesn’t affect all your CDs because pressing quality varies, even within the tight tolerances required in a CD pressing plant. Chances are that the problem will eventually occur with skip protection off as well.

10

But no one has any idea why my CD does that weird remix thing?

11

So it isn’t my CDs in other words, as soon as I get a new CD player the CDs will work fine.

12

Maybe…maybe not! A new CD player may have a stronger laser, better software, etc. but if the CD is too damaged or dirty it might not skip but it could jump or not plat at all.

13

Besides damage to the disk surface, don’t overlook the head transport mechanism. I have a BSR player from 1989 that starts acting strangely about once a year. That means it is time for me to open it up, clean off the metal slide that the plastic head transport slides on, and relubricate it lightly with silicone lube. Fixed for another year.

And I get better results with this link to Cecil’s column:

http://www.straightdope.com/columns/read/1252/since-when-do-cds-skip

14

Brains!

15

Oh Holy God! This thread’s older than I am!!

16

Wait, Markxxx asked a question in 1999 and the OP came in today and answered it as if no time had passed? Weird. Speaking of zombies, the answered question was from Halloween, 1999.

Sparky812 – are you angling to do a staff report on CDs?

17

<mod>

Zombie CDs…hmmm…new niche market?

And could Sparky be a zombie? I mean - 9 years???

Tune in next time - same zombie-time, same-zombie channel.

Closed as zombie.

</mod>