Since when do CD's skip?

My parents bought their first CD player around 1987, and that thing skipped somethin’ fierce. It was just as well they didn’t have any fun CDs, because any attempt to dance, and sometimes walk, in the same room as the CD player inevitably caused massive skipping. To be fair, this was a CD player problem, not a CD problem, and one that today strikes mainly those with portable CD players.

You might want to replace the laser needle. If it gets worn down or bent, it will get caught in the light grooves, causing skipping.

Eagles may soar free and proud, but weasels never get sucked into jet engines.

Cecil’s column is Since when do CDs skip? (04-Mar-1994)

Cecil doesn’t specifically mention it in his column, but some players are more resistant to jolts than others.

Thats for certain - I have seen a wide disparity in the resistance to skipping. A couple Xmas’s ago I bought a friend a Magnavox portable CD, and she bought me a Sony. The Sony skips if a cat walks across the room, and the Magnavox will endure light drum solos being beat out upon it’s surface.

Well, I am exaggerating, but not by much.

The Prince: “Did you kill Jahamaraj Jah?”
Lady: “Yes.”
The Prince: “My Gods! Why?”
Lady: “His existence offended me.”

CD skipping is a function of many things. There is no needle in a CD player, and there are no grooves (no offense, Slythe, but have you ever looked at a CD?). There is a laser, but it will neither wear down or bend. The laser shines through a lens onto the CD surface, and the reflected light from the pits on each track is decoded to recover the digital data. The laser is kept on track by a servo mechanism - technical lingo for a motor that moves the laser back and forth so that it stays directly over the track. As the data is read from the disk, the reflected laser signal is also used to generate signals that are used to drive the motor that keeps the laser positioned over the track.

The effectiveness of these servo mechanisms, especially when somebody starts hammering on the case, is highly variable, and it’s quite a difficult problem to make them work well in those conditions. The solution most often used is a data buffer. As the CD plays, the data being read is put into a buffer at one end, and the data you hear is being read out of the buffer at the other end. If the servo loses its position, it has some time to find the right spot again before the buffer empties out. If the buffer ever empties out, you hear a skip. Obviously, for players with no buffer, you’ll hear a skip every time the servo loses its position.

“(no offense, Slythe, but have you ever looked at a CD?)”

ZOOM!! (passing hand over head)

The earliest CD players also typically on had one laser. Almost all newer CD players have 3 beams which are better at seeing through small imperfections on the risk and responding to shock.

The better CD players also have a shock-resistant mechanism, better error correction circuitry, and larger data buffers which allow them to go back and re-read the skipped information while continuously playing music from the buffer.

Mike Palmer, when someone comes up to you and says, “Knock-knock!”, do you go to answer the door? :slight_smile:

dhanson wrote:

The better CD players also have […] better error correction circuitry […]

The error correction circuitry, as far as correcting data errors from the disk, is the same for all of them. The type of error correcting codes used are fixed, and that determines the algorithm used to fix the errors. It can’t be made better: you either implement the algorithm or you don’t. You could leave off the error correction circuitry completely, but the raw error rate on a CD is pretty high, so the sound suffers pretty significantly if you do.

A related question: how long do CDs last assuming they’re treated with TLC? Even if you don’t scratch them or coat the surface with fingerprints, it stands to reason that a disc made of oxydizable materials (plastic and metal–let’s ignore gold-plated CDs for now) will eventually give up the ghost.

One article I read in the UK mag The Wire a while back said 10 years, but that seems ridiculously low–I have CDs that are older than that & they still work fine. A friend in the record biz told me (from what I remember) “over a hundred years if you don’t scratch them or leave them out in the air”, which seems a little optimistic. --N

The way I understand it is that all CD players will skip if jolted and it is just that they read ahead and have a buffer so you do not notice it until the buffer is emptied: the bigger the buffer, the more it can skip and you won’t notice it.
that is one of the things you can see in the specs of each unit: the size of the buffer.

CD players don’t skip at all like they used to. Attribute it to better servos, better ECC, faster processors, and better shock protection(the ballooney things that the mechanism sits on…), I know they’re softer now, and the only time I’ve ever heard of issues with them is when my friend moved to South Dakota and the stabilizers would freeze, or at lease harden and skip at the slightest.

Sam Roza

There’s another cause for skipping CD’s (and DVD’s, too, for that matter): The disc is dirty. Specks of dust and dirt and water droplets will cause the laser to “lose its place.”

I was watching Wild, Wild West on my brother’s DVD and when I got to the part where West and Gordon had those electromagnetic collars around their necks, the DVD suddenly skipped the next 45 minutes to the part where Loveless was attacking the town with his giant tarantula. I told my brother and he said, “The disc is dirty,” and he showed me how to clean it.

But Wild, Wild West is a terrible movie. So maybe ny brother’s DVD is a movie critic! :smiley:

Sig Alert!

I can give you a pretty good reason. Have you ever tried reading while standing on a bus going throught bus-sized potholes at 100km/hr? That’s essentially what the CD players reading head is doing. It’s shining a light into the CD and seeing how it comes back, if the CD isn’t held completely stable (not moving in relation to the head) then the angle of light returning changes and data is lost. Oh… yeah, and I almost forgot to say that the CD has to be able to spin as well.