Theoretical question about how CD's work

Maybe Michael Green is right, after all. I.e., Lightweight systems sound better than heavy systems. The sampling rates are much higher for Blu Ray. Large capacitors and transformers in older, heavier CD players would not be good for the sound. So, it’s a little like comparing apples to oranges. I find small, lightweight (portable) CD players have inherently good sound. One assumes Blu Ray discs are subject to scattered light and vibration issues just like CD players. 

Have you flipper your gizzard? Nobody said CDs are like Laserdiscs. I already explained why laser reading is an analog process. That doesn’t mean the transitions from pits to lands and lands to pits don’t represent 1s and 0s. But those 1s and 0s represented by the transitions do not (rpt not) represent the music signal (waveform).

The laser reading of the transitions is an analog process. The laser reads, ON, OFF, ON, OFF according to whether the photodetector receives a reflected signal or no signal. The transitions occur between ONs and OFFs. And the system keeps track of the time periods between transitions. So, the lengths of pits and lands is also important in organizing the transitions into meaningful data strings, according to the Redbook standard.

The “1s and 0s” detected by the photodetector have to be decoded into predetermined strings of meaningful data downstream. As the link I provided a couple weeks ago shows there are approximately 9 or so discreet strings of data that are read off the Compact Disc. The 1s and 0s represented by transitions don’t mean anything until they’re organized even when they’re organized they still don’t mean anything until they go through a Digital to Analog Converter DAC. But, unfortunately, as I’ve stated many times, by the time the organized 1s and 0s get to the DAC it’s too late to recover from all the damage to the original data on the CD. The reasons for the damage include,

1. Scattered laser light that above a certain energy level gets into the photodetector and is interpreted as real signal. Since the laser is invisible infrared 780 nm attempts to block scattered light with green pens is only fractionally successful. There is a red component to the CD laser for safety reasons. It’s that red component of the scattered light that green pens absorb.

2. Mistracking of the laser caused by external vibration as well as vibration of the Compact Disc itself while spinning. The fluttering and wobbling is caused by out of round discs and exacerbated by the non level spinning of the disc. Mistracking occurs even though Reed Solomon Error detection/correction codes supposedly correct all errors and even though the laser tracking servo system supposedly keeps the laser on the data spiral at all times.

There are quite a few reasons why the same issue CD of a recording from different CD manufacturing plants sound different on the same CD player.

The accuracy of the process of laying down the bits and lands on the metal master.

The accuracy of producing the actual CDs from the metal master. The edges/transitions between pits and lands must be perfectly clean and correct with respect to timing (lengths of pits and lengths of lands).

Differences in the inks used for the CD label. Some inks may be more ferrous. Also if the colors of the inks are different that would influence the sound, too.

The thickness of the CD can influence the sound since a thicker CD will be stiffer and not flutter as much during play as a thinner one.

The transparency/purity of the polycarbonate layer. The nominal transparency of polycarbonate is actually only about 91%. SHM-CDs employ a more transparent material for the clear layer. Hence Super High-performance Material (SHM). Less transparency, more laser light scattering.

The purity and composition of the metal layer. Some metals and alloys have higher reflectivity for infrared light than others.

The variation in roundness of the CD. We know that out-of-round CDs flutter and flop around more than CDs that are perfectly round, causing mis-tracking.

Here’s some really bad news, especially if you purchase CDs from eBay. For anyone concerned about dynamic range on your CDs, you will find generally that CDs listed for sale are the compressed reissues. Usually, not always, the original CDs that came out in the 80s or 90s are the most uncompressed versions. This is a generalization, and I’m referring to classic rock CDs here. When an original CD of a particular album does come up for sale, especially if it’s a Japanese or German import, the price is double or triple.The trend is not your friend. Apparently everybody and his brother are dumping crappy overly compressed CDs. Which in a weird way is refreshing, inasmuch as your humble scribe is not the only person who eschews compressed CDs. 

Actually, I don’t think he did know that. As my old boss at NASA, Chuck Rounds, used to say, hit a man when he’s down. 

Exhibit A

I recently heard a friend’s (big) system that employs a clamp down device on the CD. I was able to improve the sound considerably by using my Mystery Tweak 🤫 on the CD, which stiffens and damps the CD. This, gentle readers, means the CD clamp down device is not (rpt not) effective in preventing CD vibration and flutter. Even CD Rings ⭕️ which are a good idea and address the problem I’m referring to, are not completely effective, even though they add mass to the circumference of the disc, helping reduce flutter and wobble.

kosst_amojan
Folks, I don’t think anything more needs to be said after Geoff’s last post. How can you possibly top that list of ridiculous snake oil solutions to problems nobody has ever had?

And who cares how round the edge of the CD is? That doesn’t fix track concentricity issues. CD don’t spin on their outer edge. They spin from that hole in the middle. DUH. R

>>>>>The reason out of round CDs are bad for the sound is because they wobble and flutter during play due to their mass not being uniformly distributed. Thus, the laser servo mechanism is overloaded trying to keep the laser on the nanoscale track.

Here are a few other audiophile thingamabobs that improve the sound of CDs that ought to get the 1s and 0s crowd’s blood boiling 🥵.

Nespa High intensity strobe light CD treatment

The Intelligent Chip quantum Chip for treating CDs, and the Intelligent Box (Think Inside the Box)

Audio Deske CD Improver - edge beveler for making CDs perfectly round

The PWB Violet Pen for coloring the outer edge of the CD. Interestingly, the Violet Pen also works on LPs.

tomcy6
geoffkait

You may think of it as a logic puzzle.

In that case, logic tells me that you are trying to take advantage of highly suggestible people. 

>>>>You must be channeling Juror #3 from 12 Angry Men. “You can’t prove it!!” 😡

kosst_amojan
@geoffkait

"Since everything is known and can be found in Wikipedia or some online textbook we can dismiss any inconvenient arguments as not worthy of examination. Bravo, moopman!"

You don’t have any arguments worthy of examination. Pretty much everything is known about the function of the electromagnetic force so if it’s not in a reputable book, it’s nonsense. Anyone who buys into your hocus-pocus is simply gullible.

>>>>Koost, no need to go full retard on me. you should have listened to your mommy when she told you to stay in school. You don’t even know the difference between an electromagnetic wave and a force. 😬

tomcy6
Geoff, I’ve noticed that you have frequently posted about the scattered light problem since you started selling a product to help eliminate this problem. There’s nothing wrong with that if you discovered a problem and came up with a solution.

>>>>That’s might generous of you.

It would be helpful to us and you, though, if you provided the evidence that shows that scattered light increases reading errors for cds that cd players don’t correct. If the evidence is simply that you hear a subjective improvement when playing cds treated with your product, it would be good to know that too.

>>>>I’m afraid you’ll have to take my word for it. I’ll leave all the measuring to someone else. I’ll even leave the subjective opinion to someone else. You may think of it as a logic puzzle.

fleschler
geoffkait: generic, thin, bass shy, brittle, honky, synthetic, congealed sound. That maybe your definition of CD reproduction, but it isn’t mine or half a dozen close friends of mine. While we all appreciate the sound of a good LP, the average classical and jazz CD well mastered is stunningly good. I have 35,000 LPs and 7,000 CDs. I wouldn’t give up any of them because of their format limitations. I have near SOTA front ends which permit me to extract superior performance from each format. Even my 78s sound more alive, dynamic and tonally rich compared to most audiophiles systems.

>>>>Fabulous! 😛

One wonders why the Labs 47 Shigaraki CD player doesn’t advertise the advantage wrt scattered light, compared to closed designs. I imagine some stray light scattered off the pits will get into the detector but less than closed transports, I.e., everything else. Reading one review of the Labs 47 Shigaraki CD Player I gather they have not solved the scattered light problem based on the reviewer’s description of the sound.

Apparently mapman’s butt is still stinging from something I said. Get well soon, Moops.

Just for emphasis, anyone who thinks he’s listening to all the information that’s on the disc is badly mistaken. The scattered light problem itself without even going into any of the other problems associated with CD playback accounts for an apparent loss of at least 30% to 50% of performance, in terms of bass articulation and slam, treble performance, air, resolution and size of the soundstage, signal to noise ratio, dynamic range, distortion, compared to the case where scattered light is controlled. It’s not even close, gentle readers. Geez, even a green pen around the outer edge gives a glimpse of what you can get if you control all the scattered light, not just the visible red portion. Hel-loo! 

mapman
No reason to argue about how CDs work. It’s pretty well documented. Books are still an inquiring mind’s best friend.

>>>>Ah, good one, moopman! The old Skeptics Society chestnut. 🌰 Since everything is known and can be found in Wikipedia or some online textbook we can dismiss any inconvenient arguments as not worthy of examination. Bravo, moopman!

erik_squires
I love that the OP has orphaned this thread, but people are still arguing about how CD’s work. :D :D :D

Yeah, I’m starting to think it might have been a drive by. 😬

almarg
IMO the reason many of the tweaks mentioned above by Geoff may be beneficial in some situations has nothing whatsoever to do with bit errors or error correction.

The main reason in most cases is likely to be related to electrical noise generated by the servo mechanisms and circuitry in the transport part of the player, as it tracks the disc, coupling into unrelated downstream circuitry in the player, causing jitter in the D/A conversion process, and/or intermodulation or other effects on the analog signal path. The degree to which that occurs will be dependent on the design of the particular player, of course, as well as on the condition of the disc.

>>>>Uh, I never said all the tweaks I mentioned affected bit errors or error correction. The ones I am pretty sure I can prove affect bit errors and error correction are New Dark Matter visible and invisible stray light absorption tweak, damping the CD (my Mystery Tweak) and coloring the CD, which absorbs visible stray light. Also, vibration isolation. All of those are my tweaks.

The demagnetizing of CDs and elimination static electric fields ON CDs is anybody’s guess. I don’t think anyone has explained them, at least not to my satisfaction.

note to self - I hate to judge before all the facts are in but it appears the Skeptics (capitalized for almarg’s benefit) would rather fight than switch. It certainly would not take a neurosurgeon or rocket scientist to do a little investigation and try to get to the bottom of these things. Isn’t investigation a primary part of the scientific method. And what about curiosity? Isn’t that part of the scientific method? Apparent it’s all too much trouble.

Well, the CD player in the car buffers the data, otherwise the CD would not play at all. However, data buffering cannot fix the damage already done by scattered light and the vibration CD, which occurs in the first picosecond as the laser reads the disc. So, you would have thought the sound was even more fabulous had the scattered light and CD vibration been eliminated. Everything is relative.

A lot of people think their system sounds fabulous. I get it. 😬

No matter how much you have in the end you would have had even more if you had started out with more. 😛

I suspect things are much worse than represented by almarg and his statement that perhaps 100s bits are in error. However, if that were actually true it would probably be inaudible. So, things must be worse than that. Since vibration isolation, CD disc beveling, disc coloring, CD liquid treatments, disc damping, disc demagnetization, disc static electric charge dissipation and other steps obviously improve the sound. Hell, just getting rid of the laser scattered light problem alone doubles performance! So, gentle readers, I think I’ll stick with my original evaluation that the whole CD playback system is FUBAR. I’ll leave it to others to speculate on how many errors there are on high end CD playback systems.

The OP is clearly trying to make the point that if it’s all 1s and 0s on the CD how can anything make a difference - the data on the CD cannot be changed. Hel-loo! It’s not exactly rocket science. It’s the same argument regarding digital cables. They’re both Strawman Arguments. Can we please try to be a little more chill?

Actually they don’t use mold release compound MRC during the manufacture of CDs. That’s what they call an old wives tale.

Nurse! Thorazine! Man down! Costco hasn’t been paying attention. In the case of CDs the 1s and 0s are represented by transitions not by the ON or OFF. As I already explained it’s more complicated than you apparently think. The link I provided yesterday includes the allowable sets of data determined by both transitions AND the length of pits and lands.

Also, you are incorrect that - in the Case of CDs - the digital process is reliable. It is only *partially* reliable 🤭 within limits that are set by failure of the CD playback system to deal properly with scattered laser light and vibration, internal and external. Not to mention the obvious failure of Reed Solomon error codes and the laser servo feedback system to correct all errors. Wake up and smell the coffee! ☕️

Even CD players that are *isolated* have difficulty with laser reading the data on the disc because the *CD itself* is wobbling and fluttering. The CDs are often not perfectly round and the disc is often not absolutely level during play, which exacerbates this CD vibration problem. Yes, CD Compact Disc “works” well enough for those who don’t mind generic, thin, bass shy, brittle, honky, synthetic, congealed sound.

Well, at least the world’s most sophisticated synthetic piano player. 🤭

And furthermore...

http://www.laesieworks.com/digicom/Storage_CD.html

The encoded data - the pits and lands do not actually represent digital data, not really. The laser reading process is, frankly, strictly an analog process. The series of pits and lands, their various lengths and the transitions from pits to lands and lands to pits are converted to meaningful digital data downstream. So, since the lengths of pits and lands is variable precise timing is critical to recover the data as it appears on the disc. It is not a difficult task to demonstrate that (1) Reed Solomon is only effective for certain errors, but definitely not all errors. For example it’s extremely ineffective dealing with circular scratches. It’s very good for predictable errors like scratches that are radial. Reed Solomon codes and the laser servo function are both rather ineffective for correcting errors due to vibration, including the fluttering and wobbling of the disc during play as well as seismic vibration, etc., or scattered light detected by the photodetector. Reed Solomon did the best they could under the circumstances, I guess. But that was 40 years ago, for crying out loud. 😢

A lot of errors get past the goalie. For for many people the whole thing works good enough. 🙄

All these issues with CDs and especially the player, have always been there. And there are very important reasons why CDs often sound thin, compressed, congealed, honky, metallic, brittle, bass shy, thuddy, synthetic, like paper mache.

Short answer - the laser “reads” data on the CD metal layer as a series of reflective and non-reflective areas (lands and pits). The lengths of pits and lands are variable and represent digital strings of data according to a pre-determined scheme. The actual determination of what the laser reads is determined after the laser reading operation is complete. I.e., it has to go through an interpreter.

The photodetector detects only the reflected signal (land) but doesn’t detect the signal when it is on a pit due to light wave cancellation produced by clever design of the geometries involved and the wavelength 780 nm of the CD laser. Unfortunately, the photodetector also detects scattered laser light. Since the photodetector is not too bright it thinks it’s real signal. The vibration of the CD itself produces errors during the laser reading process as the laser servo system is unable to keep up with wobbly and floppy disc.