Scratchy distortion on last tracks of CD

CD rot I suppose. It is worse close to the end of the disc due to the fact CDs play from the center out and oxidation usually starts on the outside edge of the disc. It will get worse over time. Some players may play it fine for a while. Try making a copy of it in a computer. Or if you can find a player that will play it OK use it to burn it with an outboard burner.

you might try burning a CDR of it and see if the burned one plays better. computer lasers can often extract information better than a CDP. it's a bit of a long shot, but CDRs cost about a quarter...

I've had this happen to me on several discs. Sometimes it occurs after they've aged and sometimes it happens on a brand new disc. Interesting that it's always been classical music discs. Like Rwwear says, I just burn a copy and it's always played fine.

Many thanks. But what is CD rot. Anything you can do to prevent it? I'm surprised that I've logged many, many 1,000's of hours of classical CD listening and haven't had to face it before...except for the specific pressing incident I mentioned in my post. (But then, I guess I don't have that many CD's that I listen to more than 2 or 3 times, to be honest.)

What is CD rot?

It was discovered that some CDs can have the reflective layer begin oxidizing. This interferes with the reflective quality and screws things up for the laser to accurately read the disk. Since it is oxidation, it usually starts at the outer edge of the CD - that's where the final tracks are located. Disks that are longer are more susceptible since they run tracks closer to the edge.

This is really a quality control issue at the manufacturing level (which can affect any product in any industry. Remember some of the absolutely horrid quality LP records that were released?)

Your best bet to salvage things is to use a program like EAC (Exact Audio Copy) with the error correction turned on. See if you can rip the CD to your hard drive and then burn it to a CDR. If that doesn't work, your only real alternative is to buy another copy of the disk.

CD rot is caused by moisture getting through the laquer coating that protects the reflective substrate. It usually begins at the edges because they are more susceptible to damage and wear.

Here's something to ponder.
Sony purchased about three of those monster Rockport turntables ($75,000 each, granite base, i.e. monsters).
Could they be providing a CD mastering service from vinyl
where the master tape is no longer serviceable?
The "Scratchy distortion on last tracks" is a well known phenomena for LPs.

When CD data cannot be read then it can often be perfectly reconstructed with error correction. When the CD is badly pitted (CD Rot) then the data can no longer be reconstructed using error correction and the player often interpolates between one data point and another. If it gets really bad then the CD becomes completely unplayable. One UK Plant had a serious manufacturing problem for several years in the mid eighties - there are many CD rotted discs out there - many are labelled"Made in the UK - PDO". I have four or five. It is sometimes called "bronzing" because the CD discolors too.

Mlsstl's suggestion to use Exact Audio Copy to burn a copy of the disc is wise counsel. Do it ASAP, the disc is not going to get better as time passes...

-RW-

When the CD is badly pitted (CD Rot) then the data can no longer be reconstructed using error correction and the player often interpolates between one data point and another.

I think you're getting the concepts of mathematical interpolation, "interpolation" as used in digital audio oversampling, and error-correction confused.

Mathematical interpolation is the process of deriving an in-between point from two outers. It's very processing-intensive, and quite uncommon in real-time audio DSP and data error-correction systems.

"Interpolation" in oversampling digital filters is an approximate term, usually used to describe the a combination of zero-stuffing unknown samples, and then low-pass filtering the output. It's used for its processing efficiency, and because it creates a very predictable noise spectrum, which can then be filtered out.

Error tolerance in CD transports is goverened by a number of factors, from the ability to keep the motor PLL locked, to the timing characteristics of the focus and tracking servos, the noise and accuracy of the EFM preamp and demodulator, etc. . . . and finally, "error correction" in the form of redundancy and parity in the data, through its modulation and coding characteristics. All of this happens ahead of any processing of the linear PCM data.

It is true that when data is truly gone . . . it's gone. But subtle differences in the design of the optical drive reading the disc have a huge impact on its ability to tolerate different kinds of errors, and a computer CD-ROM drive reading at high speed definately has a very different perspective on disc errors than an audio CD transport reading in real time. And if one was to design software that reads error-strewn areas of the disc many, many times, then a huge advantage can gained by averaging out noise, which enables the redundancy and parity mechansims in the EFM and Reed-Soloman techniques to work more effectively.

In short, if you get a clean rip from the CD into your computer . . . you really are getting more data off of the disc, and you shouldn't worry about whether or not you're then listening to "fake" or "interpolated" audio.