Freezing to recover distorted CD

[eddie pugh]

At the risk of being considered delusional I wish to share the following little saga with you in the hope that it may be of help to someone

I was asked by an elderly soprano in the choir I sing with whether I could have a listed to an old CD that her husband had recorded of a concert we did back in Germany in July 1978. which she said had “gone bad” and could I try recovering it. I don’t know what equipment was used to make the recording but I’m guessing a fairly competent analogue portable cassette. There is a possibility that a R2R was used by someone in our German host choir and a copy the recording made available but I digress.

The tape was transferred to CD at some point and the CD which had sounded fine for years now sounded quite bad with distortion and sibilance getting worse towards the end of the CD. The last 3 tracks being unlistenable.

I tried it on several CD Players a 1990’ish Sony ES, a 1999 Naim CDX, a Linn Karik 2 and a Sony CDR W-33 CD Recorder. The Sony CDR-W33 was the best reader but still not great.

So I tried freezing the CD overnight and made a digital - digital recording this morning of the last 3 tracks with my Sony PCM D100 portable and played it through my office recording system. To my surprise the distortion and sibilance and the pumping was virtually all gone and the tracks are all very listenable.

So much so that the CD is now back in the freezer so that I can grab the rest of the tracks in as high a quality as possible in the morning.

Interesting to note that once the CD had been in my study for a few hours and reached room temperature the distortion and bad sound was back again

I have no idea what is going on here. The CD had a slight bit of condensation on it when I closed the CD drawer and the laser took a little while longer than usual to read the TOC or so I thought.

Any ideas?

eddie

 

[Craig B]

When the CD quickly ramped up to 500rpm the condensation gave it a wash as it got flung off?

I'd give the playing side a polish using a soft cloth in a radial wipe pattern all round. Pay particular attention towards the outer circumference of the written area as this is where the last tracks reside.

If it proves to be some age related breakdown of the disc substrate then using a computer optical drive with software set to slowest read speed and maximum error correction retries may do the trick.

If you do manage to retrieve all cleanly, then keep a backup in computer data storage if burning a replacement CD.

 

[Stuart Frazer]

Have you tried to rip the CD data using something like dBpoweramp or EAC?

 

[Mr Pig]

CDs are generally very stable but you get the odd commercial one and quite a few recordable CDs that deteriorate and won't play properly. They accumulate so many errors that the CD player error correction can't process them quickly enough.

One really good fix is to copy the disk onto your computer then use the file to burn another CD. As the disk is copied to the computer, the computer's error correction will take all the time it needs to sort out the problems on the disk. So when you burn the new CD, it's been cleaned up and should play in your CD player just fine.

I've got a few dozen bad disks that I fixed this way. Worked every time.

 

[Sue Pertwee-Tyr]

For me the interesting thing here is the report that the CD, when played, sounded distorted, sibilant and became unlistenable. I thought such things simply weren't possible with CD and any data errors resulted in muting, not distortion of the analogue signal? So what's going on here?

 

[eddie pugh]

Obviously should have mentioned that EAC and dbPoweramp gave up with sync errors , also polished the CD within an inch of its life etc before resorting to the freezer
The recorded CD is probably at least 25 years old and it has a printed label stuck on the upper side so can't check for "holes" I wander if the glue has an effect on the pits !

I've had CD rot on one or two commercial discs in the past which I've been able to get over with EAC ripping and when that failed there was some address out there who would replace rotted discs for free

Thanks for the suggestions

eddie

 

[Mr Pig]

I thought such things simply weren't possible with CD and any data errors resulted in muting, not distortion of the analogue signal? So what's going on here?

The digital signal will have errors all over it. It's just that errors or poor error correction is more noticeable in the high frequencies. The distortion is not in the analogue section, it's a bad pattern of digital data. If bad enough you are right, the disk will skip, stop playing etc, but there can be significant loss of quality before that happens.

And CD players are different. Some will happily work through a disk which another player can't find the table of contents on. Depends on how good the transport is and what kind of error correction it uses. The Rega Saturn-R is interesting as it samples the disk when you put it into the machine and only applies as much error correction as it thinks is needed. I've not heard of any other player doing this. It can be annoying as it can take maybe thirty seconds or more on some disks and it's not infallible but it's a great sounding player so it's forgivable ;0)

 

[John Phillips]

... I tried freezing the CD overnight and made a digital - digital recording this morning of the last 3 tracks with my Sony PCM D100 portable and played it through my office recording system. To my surprise the distortion and sibilance and the pumping was virtually all gone and the tracks are all very listenable. ...

I have no idea what is going on here. The CD had a slight bit of condensation on it when I closed the CD drawer and the laser took a little while longer than usual to read the TOC or so I thought.

Any ideas? ...

If this is a consumer-writeable CD (I assume so - but is it?) the write laser heats a chemical dye layer on the disc and this makes it opaque in pits that mimic the pattern of pits on a stamped commercial CD.

My experience is that consumer-writeable CDs are not always long-life. High-temperature storage especially is reputed to degrade the dye layer and reduce the contrast between burned / non-burned areas so that players then have trouble.

I can guess (I don't know - maybe someone else here knows the relevant chemistry) that low temperature improves the opacity of time-faded burned areas and restores enough contrast for the drive to see fewer errors. This is definitely just a guess though and may be totally wrong.

Also, when I last auditioned CD players in 2004 using a stamped commercial CD I have that has massive bit-rot, I discovered that some drives were worse than others at correcting errors. I speculate that some CD players of that era did not implement the entire capability of the CD's C2 error correction code (maybe not enough code space in their embedded processors?). So drives of a more modern era may just possibly be better at reading this CD.

 

[mansr]

I can guess (I don't know - maybe someone else here knows the relevant chemistry) that low temperature improves the opacity of time-faded burned areas and restores enough contrast for the drive to see fewer errors. This is definitely just a guess though and may be totally wrong.

I don't know the chemistry either, but it doesn't sound entirely implausible.

Also, when I last auditioned CD players in 2004 using a stamped commercial CD I have that has massive bit-rot, I discovered that some drives were worse than others at correcting errors. I speculate that some CD players of that era did not implement the entire capability of the CD's C2 error correction code (maybe not enough code space in their embedded processors?). So drives of a more modern era may just possibly be better at reading this CD.

More likely, they differed in how well they were able to conceal uncorrectable errors.