Demagnetizing CD's !!

[Radio Wrangler]

Silly theories and silly products are probably best confined to the audiophoolery thread.

CD players have quite valid reasons why there may be differences in their sound. Digitising or re-constructing audio with a 44.1 kilosample/second sampling rate means that a fundamental going above 22.05kHz will cross over with its first alias product as that product enters the audio band, moving in a downwards direction. Oh Hell! this happens on both recording and playing conversions. So we need a fierce filter that passes up to 20kHz and then stops things like a brick wall above that.

This sort of abrupt filter has a number of inevitable problems. It will have a transient response with a very lightly damped ring, there will be phase ripples and amplitude ripples across higher audio frequencies. These are all interacting compromises. You can opt for less amplitude ripple, but everything else gets worse, snd vive-versa.

There are ways to get around this, to up-shift the sampling rate and thus only need a milder analogue filter. You still need the 20kHz filtering function, but that can be done digitally and at the higher samping rate.

So, there are numerous design compromises and variations to be played with in a CD player which are not tied down in the CD standards documents.

An error in the data proper will blitz a number of samples, error correction might fix up to some number, the machine will try to gloss over any more. The address info is more critical, it can make the machine jumt to try to get to where it thought it ought to have been, and many many samples come out wrong. So the error correction of the address component needs to be to a higher standard than that applied to the music.

I recall that an error in the coding of a Phil Collins CD put what looked like an address packet in the music stream, and that an early Philips chipset (CD150?) was jumped by this, the equivalent of a stylus jumping a track again and again on a mechanical record. Every copy of the disc pressed and on every Philips machine of the era (and those buying Philips' chipsets) Only digital technology can give you this level of certainty

David

[Techman]

Originally Posted by bluepilot

It could be that the demagnetizer is broken.

I think it is!

I haven't read through all the posts in this thread but the video on it popped up on YouTube and I watched it just hours after it was first uploaded.

Someone may have already pointed it out, but I seem to remember that when he put a recorded cassette tape on it, it didn't even try to erase any of the recording. I would have thought that it would have at least degraded parts of the recording on the tape, but apparently nothing, no effect whatsoever!

When looking inside the device it seemed that there was a large coil wound with very many turns of copper wire and some electronics apparently controlling it.

So the possibilities are...
1) It's broken.
2) It's not broken, but the (supposed) decaying magnetic field was too weak to affect the tape.
3) It's been deliberately made to 'look' complete, but has been made in such a way that it doesn't actually do anything at all other than operate an indicator light.

As for demagnetising CDs.....

[Lloyd 1985]

I wonder if it’s just a wireless iPhone charger?

[G6Tanuki]

In times-past some of my sites had a 'professional' demagnetizer that was used to wipe hard-disk-drives [everything from CDC rempaks to Larks, Winchesters, 506s and later PC-style drives] and the old open-reel magnetic-tapes/DC1200A/Exabyte/IBM3480-cartridges used on mainframe and mini- computers from the 50s through to the end of the century, before they were allowed off-site.

The demagnetizers were nicknamed 'growlers' - as in "has this disk been growled?" - because the effect of putting anything ferromagnetic on the thing's platen was indeed to produce a rather aggressive growling!

I somehow doubt this CD-demagnetizer would live up to such standards of magnetic-field-delivery.

[Craig Sawyers]

I have used dBPoweramp to rip my CD collection to a NAS drive using lossless FLAC. The software compares your rip, track by track, with all other rips using an 8 hexademinal word checksum. If your rip is bit identical with the database of previous rips, the checksum is green. If it is not identical, the checksum is red. If green, your CD title is added to the checksum library.

On the odd occasion that it was red for a track, it was usually a surface scratch of lots of pinholes in the aluminium coating.

Scratches can be polished out using 1000 grit wet or dry (used wet), until the scratch is removed. The disc looks awful at this point - dull grey. But 15 minutes with Duraglit wadding gets it back to prisitine - and it then rips perfectly.

There is no recovery from pinhole induced errors though.

Craig

[Radio Wrangler]

"Growler' has its roots in an AC energised machine used to test motor armatures for shorted turns. Somewhat before disc memories.

David

[duncanlowe]

I saw an odd issue on one of my CD players some years ago, which I can't properly explain. It was a 6 disc autochanger using a cartridge. For some reason, the rubber buffers supporting the mech, were in the wrong places, as they were different stiffnesses, to support the variation in mass of the mech. This meant that after a fairly short time, the mech dropped enough that near the centre of the disc, it started to rub on a felt pad that was part of the cartridge which was only supposed to contact the disc as it was loaded or unloaded.

Now, this contact was initially, not for a whole rotation of the disc, and would slow the disc slightly once a revolution. What I never understood, is why this slowing resulted in a drop in frequency of the played back sound, just like if you slow a record. It was like the slow down in the disc speed slowed down the D/A conversion rate, rather than causing the rate of the bits mismatching the conversion rate. Any ideas?

As a result of this fault, a particular disc that was somehow left on repeat, spent days rubbing against the felt pad and actually damaged the surface so would no longer play. I did buy a replacement copy, but then used first toothpaste, then duraglit, and did get the original working again. I think I still have both!

The player was fixed, by re-arranging the mountings to hold the mech properly. Pretty sure it's anothe item that's still in the loft!

[FrankB]

I found that cryogenically treating the CD's does improve the sound, as does cryo treating the power cord and the wall outlets.
Liquid nitrogen is the desired cryo medium. And be sure to treat all the circuit boards in the CD player with it also, as it will improve the conductivity of the traces.

The depths of audio depravity have yet to be fully fathomed.

[lightning]

Be sure to fit the £4,200 mains fuse the right way round, or you apparently won't get the promised transformation to the sound quality of your hi-fi.

[Radio Wrangler]

If you've de-magnetised your CDs and found the effect not to your taste, is there a machine for re-magnetising them?

Davd

[dave walsh]

Hi Duncan. You mentioned the Multi Player problem that you couldn't really explain [post 67]. I'm Glad to see that tooth paste and metal polish does work in the end but not ever for me/post 47* ;

Dave W

[lightning]

Here's another useful device to improve the sound quality of your CD's by trimming the edges of the disc.
Sure to make a big difference to the sound quality
Only £700

[Electronpusher0]

Originally Posted by FrankB

I found that cryogenically treating the CD's does improve the sound, as does cryo treating the power cord and the wall outlets.
Liquid nitrogen is the desired cryo medium.

Just don't drop it.

Peter

[kalee20]

I'm just wondering what the Curie temperature is for the CD's? Heating above that will demagnetise them anyway!

They may need the cryo treatment afterwards - personally, I'd go for liquid helium (-269 deg C) rather than liquid nitrogen (-196 deg C). It's much more expensive, but then if one wants the best, one has to pay for it...

[Refugee]

Originally Posted by lightning

Here's another useful device to improve the sound quality of your CD's by trimming the edges of the disc.
Sure to make a big difference to the sound quality
Only £700

So that is what it costs to get the ink off if you change your mind after marking the edge with a pen

[Radio Wrangler]

Careful, helium gas on the loose kills iphones and a number of modern gadgets through a most surprising mechanism.

Discovered in a hospital with a helium leak from an MRI scanner magnet.

David

[Craig Sawyers]

There are a number of problems with liquid helium. First is that the cooling power is almost entirely in the gas boiled off. It takes very little heat to boil and vaporize, but the gas takes a great deal of heat to warm up.

The second is that is a sneaky asphyxiant. If a large amount of helium vents into the atmosphere, it rises up, and fills the room from the top down. Unlike other gases which make you feel breathless and you get some warning that all is not well, helium has no effect until you hit the deck.

It also in the gaseous phase, as David mentioned, it has a ridiculously low arcing voltage, so can have a disastrous effect on electronics. Being a small molecule it also finds its way absolutely everywhere. And that is why it is used to find vacuum vessel pin hole leaks. There are many of the usual vacuum technology companies make mass spectrometer based helium sniffers to find leaks.

But I wouldn't use it to cryogenically process anything. Liquid nitrogen is amply good enough. At Oxford Instruments we used to rough machine superconducting magnet formers, cryogenically stress relieve them in a massive bucket dewar of liquid nitrogen, and then finish machine it.

Craig

[G6Tanuki]

If you subjected audio CDs to liquid Helium treatment, would the vocals thereafter sound like Pinky&Perky??

[Radio Wrangler]

The helium problem with some phones is ingress to hermetic packages housing micro-machined on-chip resonators as alternatives to quartz crystals. Kills the Q, stops them oscillating, bricks the phone. The stuff may diffuse out eventually.

David

[Ed_Dinning]

Hi Craig, just as a matter of interest what are the specific and latent heat figures and how do the compare to nitrogen?

Ed