BREITMAN@INTELLICORP.COM (Wallace Breitman) (02/09/90)
[This is being beaten to death in rec.audio; anyone actually TRY it? -tjk] In the current "Stereophile," February 1990, pp. 67-71, Sam Tellig, 'The Audio Anarchist,' describes a process of treating the playing side of any CD with Armor-All [Yes, *that* Armor-All we've been using on our cars for years] to improve the CD sound. As Sam described it: "Every person heard a difference with every disc, every time. Sometimes the difference between an untreated disc and a treated disc was startling -- the soundstage opened up, dynamics expanded, and a wealth of new detail revealed itself." The discussion certainly seemed to be quite serious, with no tongue in cheek. Has anyone else experimented with Armor-Alling CDs? With what results? Why would this work with *all* discs? What have the manufacturers been keeping from us? Any responses would be most appreciated. --Wally Breitman -------
midkiff@uicsrd.csrd.uiuc.edu (Sam Midkiff) (02/09/90)
In article <2299@uwm.edu> BREITMAN@INTELLICORP.COM (Wallace Breitman) writes: >[This is being beaten to death in rec.audio; anyone actually TRY it? -tjk] > >In the current "Stereophile," February 1990, pp. 67-71, Sam Tellig, 'The Audio >Anarchist,' describes a process of treating the playing side of any CD with >Armor-All [Yes, *that* Armor-All we've been using on our cars for years] to >improve the CD sound. As Sam described it: > "Every person heard a difference with every disc, every time. > Sometimes the difference between an untreated disc and a treated disc > was startling -- the soundstage opened up, dynamics expanded, and a > wealth of new detail revealed itself." >The discussion certainly seemed to be quite serious, with no tongue in cheek. >Has anyone else experimented with Armor-Alling CDs? With what results? Why >would this work with *all* discs? What have the manufacturers been keeping >from us? Any responses would be most appreciated. >--Wally Breitman >------- > My suspicion is that the Armor-All increases the transparency of the disc in the wavelengths employed by compact disc players to sample the digital signal encoded therein. This increased transparency would then have the effect of increasing the definition of individual bits, such that ones would be more "one-like" (there must be a better word for this...) and the zeroes would be more "zero-like". The resulting digital signal is therefore more binary, and the true soundstage, etc. that is encoded in the digital signal can be extracted more easily. This theory seems to hold in both directions. Coating a compact disc with peanut butter seemed to cause the soundstage to nearly vanish. A similar effect was achieved by lightly passing a #300 sanding compound over the surface of a disk. Sam Midkiff midkiff@uicsrd.csrd.uiuc.edu
brianw@microsoft.UUCP (Brian WILLOUGHBY) (02/24/90)
In article <2375@uwm.edu> jas@proteon.com (John A. Shriver) writes: >The "it's only one's and zero's" argument doesn't quite hold. It >would (perhaps) hold if there was a seperate clock signal on the CD. >There is not a separate clock however, the signal is "self-clocking", >like a local area network. The clock has to be restored from the >edges of the bits. If the transitions are sloppy, the clock recovery >will not be perfect. As Keith Johnson explained in the interview in >The Absolute Sound, 100 picoseconds of jitter (timebase error) is >roughly equivalent to a one bit error in amplitude. I can't let this go by without comment. You can't have "one bit error" when reading from a CD. There is an error correction layer which detects errors and attempts to correct them. If a CD byte were one bit off, then the player would refuse to convert this byte. It would instead either correct the bit perfectly or generate a new value by interpolation. You'll never be one step off in amplitude because of anything incorrectly read from the CD (unless the interpolated value is coincidently very close ot the adjacent value). Besides, the designers of the CD medium have already taken the "self- clocking" aspect into consideration. Each 8 bit data is actually written onto the aluminum platter as 14 bits. Thus a "one bit error" has no correlation whatsoever to the data value. Thirdly, the samples are 16 bits values and are stored as pairs of 8 bit bytes. Thus, if Mr. Johnson's explaination were applicable to the CD medium, then you would have a 50% chance of getting an error of 256 amplitude steps! >(I presume he >assumes some typical rate of change.) Needless to say, 100 >picoseconds is a damn small time. (The 350 MHz Tektronix 2564A >oscilloscope here only goes down to 5 nanoseconds/centimeter. You >would need a sampling scope to see it.) The jitter is obviously >greater than this. Anything that reduces it will help. Who cares? You can't hear this! Why do you think digital is better? >Another thing the Armor All might do is reduce the surface roughness >of the CD. One very interesting point that I learned from a series of >articles on how CD works in Hi-Fi News and Record Review is that the >surface roughness of the typical CD is 10 times greater than the depth >of focus of the laser. Needless the say, the laser focusing servo is >working real hard all the time. Since most players use the same power >supply for the laser focus as for everything else (digital, DAC, and >analog), and the laser servo is probably not Class A, the laser servo >is putting lots of crud into the power supply to contaminate the other >stages. This is the same basic argument of why damping rings, etc., >work. The CD is designed such that any (small) particles on the surface are actually out of focus to the laser, which focuses on the aluminum platter inside the relatively thick plastic encasing. Large particles can totally block the laser, but small particles can be "seen around". Generally what happens in most CD players in that the disc itself resonates and moves closer to and further away from the laser. This causes many players to stay in the error correction mode all of the time. Damping rings reduce the resonating of the CD, but any decent CD player would have a damping clamp built into the unit (i.e. even Pioneer had a unit with built in damping before the gimmicky adhesive plastic shit showed up in yuppie stores). Brian Willoughby UUCP: ...!{tikal, sun, uunet, elwood}!microsoft!brianw InterNet: microsoft!brianw@uunet.UU.NET or: microsoft!brianw@Sun.COM Bitnet brianw@microsoft.UUCP
jj@alice.UUCP (jj, like it or not) (02/27/90)
Tom,
I'd like to snip this "jitter" discussion off
right now.
The rate that the D/A convertor uses for de-sampling
is fixed not by any consideration of what the rate off the
CD is, but rather by a crystal clock that is run independantly
of the spinning CD, and to which the CD is, via a complicated
buffer-control strategy, controlled.
Hence, the only jitter in the output samples is due
to the non-symmetry of the crystal oscillator, and these
days most of the manufacturers know well to divide the clock
by a few powers of two (which has a strong and well-understood
effect on crystal jitter) in order to eliminate the jitter
problems. Sample/holds and D/A delays are much more significant
in general that the crystal clock problems.
Repeating: The rate that comes off the CD
is only marginally the same as the conversion rate
in the short term (taking into account the 14/8 expansion)
but is exactly, within 1 part/length-of-cd, the same over
the long term. The short-term rate variations are well known,
understood, and buffered completely out of the signal before
it reaches the convertor. Period.
Any effect (the existance of which I severely doubt)
from Armor-All, green ink, green cheese, disc dampers, or
the like MUST come from something other than digital recovery
issues. The hypothesis about power-supply decoupling (while
indicative of bad design) is somewhat plausible, given other
instances of bad design (some digital) in early oversampling
chips.
--
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