Demagnetizing CD's !!

[Restoration73]

As high frequency electromagnetic fields only form on the surface, it might be best to
demagnetize CDs in the microwave oven. This might also work with MiniDisc, providing
the disc does not have the sliding metal cover.

[paulsherwin]

Originally Posted by Restoration73

As high frequency electromagnetic fields only form on the surface, it might be best to
demagnetize CDs in the microwave oven. This might also work with MiniDisc, providing
the disc does not have the sliding metal cover.

Just in case the more literal minded are tempted to try this, you should *not* attempt to microwave a CD. There are plenty of Youtube videos showing people doing this - at the very least it destroys the CD, and it can wreck the microwave itself or even start a fire.

[fetteler]

I had always assumed that the IQ of the average forum user here was greater than that of a turnip - Paul's need to post (above) makes me realise that perhaps I am naive!

Steve.

[Restoration73]

Sorry, I should have qualified it "with the timer set to 2 seconds" as I don't wish to
encourage any fires.
Some years back I loaned out a basic "microwave leakage detector" (diode and edgewise
meter) and it was returned with the meter pointer vapourised. The user did not
realised it was meant to check the leakage outside the over door !

[paulsherwin]

Originally Posted by fetteler

I had always assumed that the IQ of the average forum user here was greater than that of a turnip - Paul's need to post (above) makes me realise that perhaps I am naive!

This is a public forum, and you don't need to be a member to access posts. People come to posts as a result of random Google searches, and often read them out of context or without an appreciation of the forum culture. We don't want to encourage halfwits to burn their houses down

[Radio Wrangler]

I believe that the CD and microwave experiment was once carried out on television by a certain Mr Clarkson, whose engineering nous has been repeatedly shown (also on television) to be not too dissimilar to the aforementioned turnip.

David

[dave walsh]

I'm staying away from magnetic fields and CD's but it makes me think about Eric Laithwaite and the Mag Trains [as demonstrated on yesterday's Look At Life film-on TPTV yesterday The coding info given here is very interesting [even if I don't really understand it-probably a turnip]

Further to cleaning CD's and DVD's [just to get them to play, not be "super enhanced" post 38*] All sorts of things have been recommended in the past eg toothpaste/metal polish and stranger suggestions, usually with a slightly abrasive action and worse [not as a Hi Fi product of course]. I've found methylated spirit applied fairly vigorously usually helps or at least if it doesn't nothing else will

Not being very good at repair and maintenance I find that my CD and DVD machines now have to be treated with even more as they age. Strangely a bit like Steam Engines which have to be coaxed into action even though they might have been fully restored]. Discs seem to respond better with a meths when there a fault reported. Even if that clears electronically I still do a clean before returning the disc.

Going back to the lack of digital awareness [mentioned by Paul Sherwin] I recall using VHS tape for audio at one point when I realised how superior the audio spec had become on VCR's. Is it possible that some unaware individuals have associated the magnetically based Video Cassette with digital media. Unlikely but possible I suppose!

I think that, overall, audio recorded on CD or DVD is already of a pretty extraordinary quality [compared with a few decades ago] Leaving out the "Vinyl is always better view" everything is subjective in the end really.

Dave W

[Radio Wrangler]

Originally Posted by paulsherwin

It's more that radial scratches confuse the tracking less, so the laser is less likely to lose the data track.

The cross-interleave coding and the correction algorithm spread the redundancy involving each bit around a bit. The aim is to be able to dodge a blemish of typical size interrupting reading of a track, while not spreading the stuff that needs to be remembered and saved too far in the path of the reading/tracking motion.

So it can best correct scratches oriented radially. Scratches following the direction of reading destroy too much of the redundant coding population and correction performance is a lot poorer.

By the time a radial scratch (or the famous drilled hole) comes around again, the decoder has built up a reserve of good data to allow the missing bits to be reconstructed.

Some of the tricks played in the coding and error correction processes of the CD are quite impressive.

For recording data, much more capable error correction is employed as the use of the output data is considered to be more fragile in terms of uncorrected errors. So the amount of redundancy coded into the data put on the disc is larger than the audio CD. This is why a data disc has lower capacity than you'd expect from the specs of the audio disc.

David

[Lloyd 1985]

So has anyone tried magnetising a CD yet?

[MotorBikeLes]

A radial scratch is obviously shorter than a circumferential one, hence the latter being much worse.
I seem to remember there was a length (a mm or so) that could be recovered. More than that, you put your fingers in your ears.
What the width of those radial marks Philips demonstrated would have been less than the correctable length.
Les.

[G.Castle]

Originally Posted by Lloyd 1985

So has anyone tried magnetising a CD yet?

I like the way you think! May be easier to prove it does no harm than trying to improve something that isn't causing a problem.

[duncanlowe]

I wonder if any of the 'phools, have considered the laser assembly? I have come across issues where a deck would appear to have failed because it was no longer able to read the (data) DVDs it was designed to, but was still happy to read CDs with similar data on. In fact it was such a well known issue that the test was for a failed drive, to try a CD. If it worked when the DVD didn't a laser replacement was a fix. Allegedly it was down to the damping fluid in the lens focus assy that thickened up. I don't know how true, but certainly I have such a drive that exhibited the failure, and a new laser fixed.

Could we sell some specially modified, demagnetised damping fluid?

[paulsherwin]

CDs and DVDs use different lasers. It's possible for one to fail while the other is OK.

[Radio Wrangler]

Combining CDs, Magnetism and the mention of Eric Laithwaite. I used to have a Sony CDP302ES and one of the bullet points on its marketing brag-sheet was that the laser was moved across the deck by a linear motor.....

Hmm, there are quite strong magnets in the CD drive to do this, whatever sort of motor, and if CDs are susceptible to magnetisation... Oh dear!

David

David

[lightning]

lf you fancy a laugh then look at posh hi-fi interconnects.

Now l realise that better speaker cable can make a difference but there is a point at which there is no more to be gained.

Not according to the cable manufacturers, who make all
sorts of claims about their cables.

lt's the prices that are shocking. One company sells a 1.5m mains lead for £30,000
Won't reach? No problem, the 5m one is £50,000

And £100 for a fuse. Apparently you'll get better blacks on your LED TV if you fit this fuse in the plug

[agardiner]

At risk of going OT, wonder if you can buy a £700 aerial for your DAB portable that improves the bit rate of the transmission?

[Craig Sawyers]

Originally Posted by lightning

And £100 for a fuse. Apparently you'll get better blacks on your LED TV if you fit this fuse in the plug

Oh - that is cheap. At the hairy end of this daftness you can pay £4,200 for a fuse - the Quantum Science Audio Silver Extreme Level UK 13A Fuse.

As I've said before, any audio product that uses the word "quantum" is by definition snake oil.

Craig

[paulsherwin]

Can we stay on CDs in this thread please. Some OT posts have been trimmed.

[cmjones01]

I feel pretty well aware of how CD error correction works, but have noticed an interesting failure mode in the past. Back in the days when we used to record music on to CD-Rs, I found a couple which I'd recorded which had started to fail after a few years. When played on a standard domestic CD player they played without skipping or jumping (presumably because the 'track' is permanently written to the CD-R at time of manufacture) but the audio sounded like a weak FM radio station, with very noticeable white noise in the background. I never had chance to investigate further but am curious to this day about what was going on in the player's error correction circuits!

Chris

[lightning]

l was always aware that CD was a digital medium but the sound you get from a CD player is obviously dependent upon the processing circuitry, l've had CD players that sound harsh (a bit like Windows Media Player)
And others that sound lovely, with a warmer sound more like vinyl.