> On May 7, 2024, at 1:15 PM, CAREY SCHUG via cctalk <cctalk@classiccmp.org>
> wrote:
>
> my ears would never be good enough to notice any difference....
>
> For what it's worth:
>
> First, in general, there are so many apparent reviews of so many products, it
> is hard to believe they are all scams. How can there be enough fools to buy
> enough of those products to have that many different ones? I mean, it takes
> a lot of work to develop a product, if you only sell 5, it is not worth it.
> if you take money and don't send anything,t hat would show up in a google
> search.
>
> also, what some hinted at is the issue is even a very slight amount of
> magnitsm, spinning very fast, could affect the signal in the playback head....
A CD or DVD "demagnetizer" is by definition a scam and an utter fraud. Those
media are non-magnetic and in any case magnetism plays no role whatsoever in
reading them.
Also, keep in mind that something may look like a review but it's actually a
press release, perhaps slightly warmed over.
> Do CDs and DVDs have parity and or checksums? If you grab a CD twice, will
> both results be identical bit for bit?
They go way beyond checksums, using sophisticated ECC schemes. There's a good
reason why a scratched disk can, in most cases, be read without trouble. I
remember reading years ago that someone showed off the CD ECC scheme by
drilling a hole into a CD (2-3 mm or so) -- it read just fine anyway.
So yes, unless the disk is damaged beyond the power of the ECC, it will read
correctly every time. And even if it does exceed the ECC, it will in most
cases read the same, though some bits of data will be unrecoverable. You'd
have to go WAY beyond the ECC limits to reach the point of undetected data
errors, i.e., a misreading of the data that the ECC doesn't catch (let alone
correct).
That property holds for all codes, in fact. Every one of them has a set of
error patterns it will detect, a set it will correct, and a set it will miss.
The design challenge for codes is (a) understand the likely error patterns it
will be confronted with in the wild, (b) understand the required probabilities
for (1) uncorrectable and (2) undetected errors, and (c) to create a good code
that delivers on these requirements efficiently. "Efficiency" is defined by
coding overhead as well as implementation cost.
>
> https://www.gcaudio.com/tips-tricks/cd-dvd-demagnetization/
>
> https://forum.audiogon.com/discussions/if-you-have-a-cd-player-you-need-to-do-this-periodically
>
> At first, this SEEMS even more ludicrous, demagnetizing vinyl LPs, but the
> pickup heads are analogue magnetic, so maybe more reasonable
> .
> https://www.canadianhifi.com/shop/analog/accessories/furutech-demag-a-lp-cd-cable-demagnetizer/
What an amazing pile of bunk.
Some years ago I was joking about the possibility that someone would sell gold
plated fiber optic cables to suckers like that. Imagine my surprise when,
somewhat later, I spotted Monster fiber optic cables with gold-plated
connectors.
paul
