>recently i got an album from somewhere
its actually a sound system burn in tracks CD
inside the CD theres this demagnetizing track

>i wonder if it really works. is it 50% true or 50% psychology issue here ? or is it a placebo effect?

IME 100% psychology. Ditto for Bedini Clarifiers and the like.

A so-called "demagnetizing track" consists of a sinewave with an amplitude that decays to zero. I put such a signal on Stereophile's Test CD 3 to allow readers to try it for themselves -- see http://www.stereophile.com/features/424/index8.html.

As to why a decaying tone might (note I said "might") have a beneficial effect, this is exactly what you do using, say, a tape-head demagnetizer to demagnetize the tape path components on an analog recorder. The AC signal destroys any residual DC magnetism, then as the tone decays (or is removed to an "infinite" distance), the component is left in an unmagnetized state.

So: _if_ the components in someone's audio system contain ferrous materials and _if_ those ferrous components are in close enough proximity to the signal path to matter (some resistors have steel leads, for example), and _if_ those components have somehow become DC magnetized, and _if_ the decaying tone is of a high enough level, and _if_ it produces an AC magnetic field in the proximity of the affected components, it _might_ have a beneficial effect.

A lot of "ifs" but a 1978 AES paper from some Kenwood engineers showed measurable distortion from ferrous materials in close proximity to an amplifier's signal path. I don't think it coincidence that most good-sounding high-end electronics use aluminum rather than steel chassis.

John Atkinson
Editor, Stereophile

>As to why a decaying tone might (note I said "might") have a beneficial effect, this is exactly what you do using, say, a tape-head demagnetizer to demagnetize the tape path components on an analog recorder. The AC signal destroys any residual DC magnetism, then as the tone decays (or is removed to an "infinite" distance), the component is left in an unmagnetized state.

The critical fact that is not presented above is the fact that magnetization and demagnetization are generally highly nonlinear effects. IOW a magnetic field strength of one unit might have no effect whatsoever on a magnetized object, while a magnetic field strength of two units might be capable of fully demagnetizing it. It often takes quite a strong magnetic field to demagnetize an object, one that is stronger than any that might be encountered in typical use, and one that can easily be stronger than can be created by any normal operational signal.

Consider the classic tape head or magnetic tape demagnetizer. They both generate magnetic fields that are vastly stronger than found in a recorded magnetic tape, and by integer multiples. If you've ever moved a tape head demagnetizer near a tape head in an tape recorder that you are listening to, the buzz that is generated in your speaker will be vastly greater than bass from even the loudest musical passage.

>So: _if_ the components in someone's audio system contain ferrous materials and _if_ those ferrous components are in close enough proximity to the signal path to matter (some resistors have steel leads, for example), and _if_ those components have somehow become DC magnetized, and _if_ the decaying tone is of a high enough level, and _if_ it produces an AC magnetic field in the proximity of the affected components, it _might_ have a beneficial effect.

One kind of evidence for the fallacy of sighted evaluations is the number of similar effects have captured strong believers in similar effects that are based on so many iffy situations that they are simply not credible.

For example I have an associate who has supoorted his speaker cables on glass telephone insulators because he thinks he has heard bad effects from the steel in the reinforcing bars that may be in the floor of his listening room in a sighted evaluation.

>A lot of "ifs" but a 1978 AES paper from some Kenwood engineers showed measurable distortion from ferrous materials in close proximity to an amplifier's signal path.

Please see former comments about measurements being orders of magnitude more sensitive than reliable listening tests.

>I don't think it coincidence that most good-sounding high-end electronics use aluminum rather than steel chassis.

Aluminum is far more transparent to hum pickup than steel. Putting transformers in tight steel boxes is well-known to reduce their ability to induce hum on nearby components. Steel partitions are used in some equipment to reduce hum pickup from power transformers.

At least one high end audio production supplier has made a business of selling CD's of "analog dither", a significant component of which is hum.

A little hum can give the subjective impression of "warmth".

Tape playback heads are sheilded for this reason. The question of high end amps being built out of aluminum is actually due to the fact that most builders can't work steel into designs. Aluminum can be extruded easily into heat sinks and panels and rack handles. All of my gear does however have steel top covers and chassis parts.

There is nothing to demagnatize in the signal path of a phono amp, amp, speaker system. (OK, the speakers have permanent magnets, but surely you don't want to de-magnatize those! ;-)). It is beyond me why anyone would believe that an aluminum and plastic CD or an electronic circuit consisting primarily of copper and glass could be magnatized in the first place.
The only things that can be magnatized and may be de-magnatized in an audio system would be a tape head as mentioned earlier or a phono cartridge. While de-magnatizing a tape head should be a good practice, I cannot recommend de-magnatizing a phono cartridge which like a speaker, also uses permanent magnets.
-Bill

Quote:
A so-called "demagnetizing track" consists of a sinewave with an amplitude that decays to zero.

Ayre/Cardas has a "demag" CD which consists of a glide-tone which sweeps from low-to-high.

http://www.amusicdirect.com/products/detail.asp?sku=ACARCD

Densen hsa their "Demagic" CD, whose demag track is a pretty bizarre set of tones at various frequencies and amplitudes.

http://www.amusicdirect.com/products/detail.asp?cat=&sku=ADENMAGIC

I've tried them both and heard some different before/after...but not enough to convince me it wasn't completely in my head...