Testing audiophile claims and myths

[bigshot]

There are plenty of unmeasurable sounds that are imaginary too... bias and placebo are two big causes.

 

[colonelkernel8]

None idiophile device.

It is, basically, a thin disc that is placed atop the CD ( or better yet, DVD ) in all top loading and tray loading transports. There have been special paper, graphite and carbon fibre mats sold for this purpose. In practice, 0.2 mm ( or thereabouts ... ) mm thick carbon fibre version proved to be the most durable.

It is required in all transports that do not offer the support for the optical disk across its entire surface. Why, do you think, older Pioneer CD players and CD-R/RW recorders with "turntable" support in the exact size of the disk, on which you place CD with the recorded side facing up/towards you, are creating bidding wars on ebay - if and when they appear for sale ?



Naturally, turntable style CD transport costs more than standard variety - and reading errors that do occur in real time ( listening directly from a CD player, without the possibility for as many "passes" as required for perfect rip ) then have to be corrected for. No matter how sophisticated is error correction system/algorythm - it can NOT beat no error ( or, at least, less errors ) offered by turntable style support or, next best thing, CD mats used atop CDs ( or DVDs) in standard transports.

There is one application that requires warning :
DO NOT USE CD MAT IN ANY CD-DRIVE THAT (CAN) OPERATE AT MORE THAN ABOUT 4X NORMAL SPEED - such as with CD/DVD burners.

Dimensions of CD hole, CD spindle clamp and CD mat have some tolerance; and it is possible that clamp will not clam the mat 100% in centre each and every time. If spun faster than about 4x, it can create havoc. I grew a custom to tick each and every box in whatever CD/DVD burning software to bring the speed of rotation DOWN - and as an extra precaution, burn at first a normal CD-R without the CD mat ...- since sometimes various settins interfere with each other and the computer will try to e "helpful" and increase the speed. This unfortunately also prevents verification of the written data at the end of burning - as this operation can not be made to turn more slowly, but will usually run at max speed the drive used is capable of. Most definitely not something one would want ...

There are also exceptions where the use of mats is impossible; those drives that only have a very narrow slot in which the optical disk is inserted. That additional 0.2 mm simply does not go in. Among others, Yamaha has such drives.

The diff use of CD mat can make ? A friend cursed me for not having demoed the CD mat to him before he replaced his CD recorder with newer CD player - because the new CD player no longer had the edge over older CD recorder ,but now using CD mat - the very reason why he purchased the new CD player in the first place.

It was inevitable - everything invented in the West gets copied, sooner or later, at a much lower cost in China. The first hit for CD mat on today's ebay :
https://www.ebay.de/itm/0-2mm-Kohle...566190?hash=item34085c4d2e:g:ZZ0AAOSwtLNcrxVZ

lol. I don't think you understand how ridiculous this is. Does the laser impart a force on the CD greater than something measured in femtonewtons? I just don't understand why you're here. "Demoing" a product is not the same as testing it. I'd bet every penny I make for the rest of my life that a CD mat does absolutely nothing to the signal in an already functioning CD player. Plus, read errors don't manifest themselves as "less bass" or "too much treble" or god forbid "narrow soundstage", they manifest as skips or pops.

 

[colonelkernel8]

More than OK. I went to sleep in between those two posts - saw yours first thing in the morning after turning on the PC.

TBH - you can go to hibernate like a bear over the winter while awaiting the CD mat test. But, spring WILL come.

Here's a test: get a cheap USB logic analyzer or oscilloscope. Connect SPDIF output of CD player under test to it. Compare output from CD with mat and CD without mat. Determine objectively that the data is completely identical. Change your mind.

I know, the last part is a stretch.

The Salae Logic 8 from https://www.saleae.com/ will get you there. The software it runs can save the output from each test as a bin file you can then do a compare of.

 

[KeithEmo]

I'm not sure who you're replying to... but I absolutely agree with you there.
With current technology, we are ABLE to measure virtually anything with more precision and accuracy than human hearing, so anything which is audible should certainl;y be measurable.
The catch is that sometimes the data is so complex that it exceeds our ability to ANALYZE it effectively.
(Our huamn brains are still apparently able to correlate large quantities of data in ways that we are unable to do by machine - at least so far.)

For example, I could digitize a copy of my favorite Rembrandt painting with sufficient precision to be able to see the individual brush strokes, and the strands of fiber in the canvas.
I could also make a scan of similar precision and detail of the painting on my wall that I purchased for $25 at a garage sale.
I have little doubt that those two scans would contain enough information to allow us to determine which painting is the Rembrandt (and which one is more attractive)
And, with modern AI, I could probably find software that could even guess, with some degree of accuracy, which one was painted by Rembrandt.
However, as of now, we cannot measure "why the Rembrandt looks much better than the garage sale painting".
In other words, we have sufficient measurements, but what we lack is the ability to fully interpret them.

I have no doubt whatsoever that, if two DACs sound audibly different, there are one or more measurements that will show that difference.
The problem is that, if you measure any two DACs, you will find MANY differences in their measurements.
I have never seen two DACs with IDENTICAL amounts of distortion and noise, and IDENTICAL noise spectra, and IDENTICAL spectra that might or might not be entirely due to jitter.
Look at the filter responses to various types of transients... you will see differences.
Look at the actual noise spectra at the output... you will see differences.
(Apply a signal with jitter at the input... and you will see differences in the differences that appear.)
It is circular logic to claim that "well, yes, there are all sorts of measurable differences, but you're sure none of them individually or in combination, is audible", and then go back to claiming that the measurements show nothing.
In fact, the measurements we already have show all sorts of differences, and there are probably many more measurements we haven't done yet....
So, if there is an audible difference.....
Maybe we haven't measured all of the right things...
Maybe our measurements aren't accurate enough...
Maybe we're wrong about some of those presumed "thresholds of audibility"...
Maybe the difference is due to some error we've made or some external factor we haven't thought of...
(Maybe, when we listen to five DACs in a row, the first one always seems to sound great, and the fourth one always seems to sound bad.
We can test for this by varying the order of our test samples the next time we perform the test. )
Or maybe the difference really isn't there...

The problem, which isn;t really a problem, is that there are a lot of maybe's there.....
Claiming that you know everything that matters, after taking a few simple measurements, is an oversimplification.....
(And, yes, sometimes the simplest answer does turn out to be the correct one... but not always... and perhaps not even usually.)

I'm interested to know about any PROVABLY (as in blind tested) audible sound quality that isn't also measurable in some way.

 

[KeithEmo]

I am slightly confused about one thing you said....

The W4S DAC2 offers a choice between several filters.... and, as I recall, one was claimed to be the most accurate. However, because a reconstruction filter is required for the DAC to perform properly, there is no option to choose not to use any of them... so you were in fact always using one of the filters.

(Some niche DAC vendors actually do avoid including a filter, at which point the bandwidth limitations of the other analog circuitry act as a sort of informal and ill defined filter, with largely unknown and variable response parameters. However I'm pretty sure that Wyred4Sound didn't offer anything goofy like that on the DAC2 - at least not on the version I owned. )

Thanks for the specifics.

The inexpensive Turtle Beach cards had problems but I doubt it they were specific to the DAC. As they were tanking years ago, they released a number of poorly written drivers and used nonstandard interrupts. They didn’t seem to be too concerned about following Windows standards so they exhibited a number of odd issues. No argument that they sounded bad.

Can’t agree with you on the W4S DAC2. I’ve owned one for many years (since the DAC2 was first released) and unless one of the filters was selected, I’ve found it to be neutral as has everyone else who has listened to it. I’ve run a number of blind tests with it and no one has been able to pick it out from any other DAC it’s been compared to. I still have it- happy to setup testing for anyone who would like to participate.

 

[KeithEmo]

I think you're missing the point of the claim itself.....

If the "turntable style CD player" fails to clamp the CD tightly, then it will probably vibrate as it spins (surprisingly - many CD transports are not built to very tight tolerances).
And, if the CD vibrates too much, it could cause the LASER to mistrack, which could cause data errors.
And, if there are sufficient uncorrectable data errors, their presence could be audible.
(As someone suggested, if this were the case, I would expect clicks or skips to be the obvious symptom.)
And, IF THIS WERE OCCURRING, a mat or clamp that reduced the vibration might reduce the number of data errors.

For whatever reason, even though a standard CD transport mechanism actually internally "knows" whether uncorrected errors have occurred or not, that information is usually not available.
The manufacturer of the transport mechanism could include an LED which would illuminate to assure you that the data you were receiving was perfect and error free - but they do not.
(I've always though it would be a good feature to include.)

I would personally consider that any CD transport that was susceptible enough to the effect to be a badly flawed design.
(That's one reason why I prefer to RIP CDs on a computer - and part of that process is a final verification to rule out the possibility that any uncorrected read errors have occurred.)
Likewise, standard commercial CD transports have excellent error correction, and so should repair most if not all such errors.
And, as someone already suggested, it should be simple enough to analyze the output data using separate software, and determine if this is happening or not.

However, since so many high-end CD players use custom designs, and even custom electronics, I would not assume that this applies to all current existing models.
(Since many use custom, non-standard components, we cannot rule out the possibility that they have unusual problems, which may be improved by unusual solutions.)
That's why it makes sense to thoroughly test claims like this...
(Or, if you prefer, simply avoid the types of CD transports that are likely to have this sort of problem.)

lol. I don't think you understand how ridiculous this is. Does the laser impart a force on the CD greater than something measured in femtonewtons? I just don't understand why you're here. "Demoing" a product is not the same as testing it. I'd bet every penny I make for the rest of my life that a CD mat does absolutely nothing to the signal in an already functioning CD player. Plus, read errors don't manifest themselves as "less bass" or "too much treble" or god forbid "narrow soundstage", they manifest as skips or pops.

 

[bfreedma]

I am slightly confused about one thing you said....

The W4S DAC2 offers a choice between several filters.... and, as I recall, one was claimed to be the most accurate. However, because a reconstruction filter is required for the DAC to perform properly, there is no option to choose not to use any of them... so you were in fact always using one of the filters.

(Some niche DAC vendors actually do avoid including a filter, at which point the bandwidth limitations of the other analog circuitry act as a sort of informal and ill defined filter, with largely unknown and variable response parameters. However I'm pretty sure that Wyred4Sound didn't offer anything goofy like that on the DAC2 - at least not on the version I owned. )

I believe the default settings for bandwidth and IIR are supposed to be the most accurate and those are the settings I use. You are correct that that does employ a filter - my original post was poorly worded.

 

[bigshot]

My amp has a built in equalizer and tone controls. That doesn't mean the amp isn't clean and flat.

 

[analogsurviver]

Here's a test: get a cheap USB logic analyzer or oscilloscope. Connect SPDIF output of CD player under test to it. Compare output from CD with mat and CD without mat. Determine objectively that the data is completely identical. Change your mind.

I know, the last part is a stretch.

The Salae Logic 8 from https://www.saleae.com/ will get you there. The software it runs can save the output from each test as a bin file you can then do a compare of.

Thank you for the link - it may be helpful.

Unfortunately. this test, although perfectly valid, does NOT reflect reality - not in real life.

That's why I said I want to make it better. I did figure it out how, now I will have to learn something I never needed to do up to this date : cut both samples to exactly the same length, with exactly the same beginning and end, and then perform null test.

I am FAR more interested in analog record playback than I will ever be in digital audio; I have to figure out how to change PCM ( grrr - unfortunately, DSD can not be processed ...) recordings from test records into some meaningful graphs. The biggest problem are ticks an pops, inevitable even in new records. As most measurements of phono equipment are linear ( without the RIAA filter required ), this is even more exaggerated in digital recordings of output from analog test records. There is a reason why the latest software plus proprietary test records cost so much... because the bulk of the work has been to determine best algorithms how to get rid of the ticks and pops while having no or minimal influence on the graph produced. I am interested in working with old non plus ultra test records from the golden age of analog, long out of print and today next to unobtainium, at any cost - simply because they were and continue to remain the best.

 

[Killcomic]

Why is it that every time I come here there’s someone arguing that their invisible friend exists?

 

[analogsurviver]

lol. I don't think you understand how ridiculous this is. Does the laser impart a force on the CD greater than something measured in femtonewtons? I just don't understand why you're here. "Demoing" a product is not the same as testing it. I'd bet every penny I make for the rest of my life that a CD mat does absolutely nothing to the signal in an already functioning CD player. Plus, read errors don't manifest themselves as "less bass" or "too much treble" or god forbid "narrow soundstage", they manifest as skips or pops.

Oops.... - somebody talking theory, without ever recording music ( and by that, I mean REAL music - musicians/room/microphones/some kind of storage ) in real life.

Nope, assuming optical disc playback to be perfect is NOT how it is in real life. Be nice and re-check the size of the CD pits - and then put any of your beloved CDs with hole on any of your fingers that fit into that hole. Flick the rim of the CD with the fingernail of the other arm - close to your ear. You WILL hear the CD vibrating.... - with amplitude exceeding the pit size. Forcing the laser serve to perpetually search for the focus.

Now repeat the same test - this time with the paper that comes in all/any CD-R media on top of the CD-R stack. You WILL hear much less of the CD resonance, both in amplitude and in duration - it is over almost instantly and does not ring like CD normally does. That paper of course can not compare to the effect of the mat - where probably the best is graphite, but so thin graphite disk is brittle to the max and most likely anything but durable. Next best thing - carbon fibre mat. While probably not as good as graphite, with reasonable care it will last in normal 1x speed transports such as CD and DVD player for a lifetime.

Of course, no one is flicking the rim of the CD while playing back - at least not with the magnitude of fingernail. Then again, re-check the size ( depth... ) of the information pits of the CD ... - and then, DVD. It is likely DVD benefits because of this even more than CD. Anything that rotates is bound to vibrate to some extent - no such thing as perfect bearings with zero free play and noise.

CD mat has another advantage - optical. CD-R ( and CD ) media is NOT entirely non permeable for light - just check some different samples looking trough them to a light bulb. Some are at least semi-transparent - and likely to be more or less so, depending on any label printing or graphics - meaning optical conditions are NOT uniform, but are changing according to whatever is on the label. Placing a black carbon fibre mat on top of the label will instantly make this translucence problem ( again, a possible source of forcing laser servo into constant focus correction ) obsolete. For each and every CD in your collection.

Unless you have "turntable type" CD transport - then no mat is required.

 

[gregorio]

[1] I'm beginning to suspect that I know a lot more about nuclear fusion than you do....
[1b] but I'm beginning to lose interest in explaining it ....
[1c] or in arguing about the semantic details of how violent a fission reaction must be for one or the other of us to classify it as "an explosion". (However, as an example, it clearly is not going to serve our purpose here... )
1d. I'm still waiting to see the part that isn't true.

1. and Wikipedia apparently, and not just about nuclear fusion but also flying pigs, 1mW office sound systems, etc.!
1b. If only!
1c. You've already classified it, you keep mentioning Hiroshima and Nagasaki.
1d. Duh, the part where you claim that someone hitting two blocks of plutonium together will cause a nuclear explosion.

[1] Since you seem so sure that "the level of audibility for jitter is well known" and "modern equipment is all far below it", perhaps you can tell me why so many people seem worried about it....
[1b] Perhaps they don't agree with YOUR opinion about what level is audible.
[2] The result [of a J-Test] is interesting - it just isn't telling you those things.... so they go untested.
[3] I agree, the levels of jitter present on modern equipment are difficult to measure "because they are so low".... However, claiming that this also "proves" that they are inaudible is the circular argument....

1. You're joking right? You mean apart from marketing BS and ignorance of the reliable evidence/science?
1b. Great, then they'll have some reliable evidence that contradicts 45 years worth of reliable evidence/science, let's see it!

2. Clearly that's a lie. You've been given (and you've quoted from!) a paper where "those things" were actually tested (not using the J-Test). Additionally, there are internationally recognised procedures for measuring jitter and commercially available equipment to carry out those procedures (again, not the j-test). Why would anyone design test equipment to test for something that "goes untested"? This is just ANOTHER rewording of one of your (and audiophilia's) favourite fallacies, YOU don't know (or YOU don't test) and therefore science and no one else does either.

3. It would be a circular argument if I had made that claim but I didn't. Completely misrepresenting what was actually stated and then refuting that misrepresentation is just ANOTHER repeat of one of your fallacious tactics!

It's like a broken record; accused of peddling fallacies, untruths/lies/misrepresentations, your response is to peddle fallacies, untruths/lies/misrepresentations, WHY? Don't you realise that it's ridiculous, insulting to this forum and just confirms the accusation? How does that benefit you or your company's reputation?

I wouldn't necessarily expect 100 picoseconds of sine wave jitter at 3 kHz and 100 picoseconds of random jitter at 0.1 Hz to be equally audible.

I would necessarily expect 100 pico-secs of jitter at 3kHz and 100 pico-secs of random jitter at 0.1Hz to be equally audible. I "would necessarily expect" this because all the reliable evidence over the last 45 years or so tells us that both are not just inaudible but more than an order of magnitude below audible. So the question is, WHY you "wouldn't necessarily expect" this, what are you basing YOUR expectation on? Is it some/any reliable evidence or is it ignorance/stupid, marketing requirements and/or audiophile "impressions"? As you've never even stated there is any reliable evidence to support your expectation, let alone presented it, that ONLY leaves one or more of other options!!!!

[1] To me, it makes more sense to approach the question from the direction of: "We've identified a difference, which multiple people claim to hear... let's confirm that it's really there."
[1a.] "Then, once we've done that, we can proceed to some theories about what's causing it, and some experiments to determine which of those theories might be correct."
[1b] However, it is not good science [1c] to simply ignore claims made by others because you can't find a theory to explain them.

1. If it "makes more sense" to you then why on Earth don't you do it? Are you saying that you have no "sense" or, is this just more hypocrisy?
1a. Firstly: But you haven't "done that", you haven't confirmed it's "really there" or reliably confirmed that it's audible! Secondly, YOU do NOT then proceed to some "theories", you don't even proceed to some "hypotheses" because even an hypothesis requires some supporting evidence. What YOU actually do is invent some nonsense "possibility" which contradicts the science, with no reliable supporting evidence whatsoever! Lastly, But YOU don't devise some experiments to determine which of those "theories" (nonsense possibilities) might be correct. What YOU actually do is invent some ridiculous analogies and then effectively demand that we/science prove that your nonsense "possibility" is impossible (which of course it can't because science can't prove a negative)!
1b. It's difficult to even imagine anything further from "good science" than what you're doing, it's anti-science. Congrats, a whole new level of hypocrisy!
1c. And, just to top it all off, a lie, you really are going for a royal flush on this one! CLEARLY, we DON'T "simply ignore" claims made by others. We compare those claims with the science/reliable evidence and if those claims contradict the science without any reliable evidence, only then do we ignore them. Furthermore, we CAN find a theory to explain them, in fact a very well documented, tested, demonstrated and well established theory (cognitive bias for example).

Let use one of your own examples to demonstrate the above:

"For example, the AD1986 ASRC is specified to deliver an output signal whose output is "identical to what it theoretically should be down to about 132 dB" - but they entirely fail to specify what the actual differences may be. So, perhaps those unspecified differences to account for the fact that so many people insist that they hear a difference between when that chip is engaged and when it is bypassed." - Let's assume the the specified performance is correct. Firstly, have you "confirmed that it's really there"? Have you measured the output of speakers/HPs to confirm they are actually outputting any differences (whatever they may be) at 132dB below peak? OBVIOUSLY you haven't because there are no speaker/HPs capable of that. Have you reliably confirmed it's audible? OBVIOUSLY, you haven't and OBVIOUSLY It would be impossible for something which can't be reproduced to be audible! So, you have NOT fulfilled the conditions that YOU stipulated and you proceed directly to "some theories". Secondly, your "theory" ("perhaps those unspecified differences ...") is not a theory, it's just a "nonsense possibility" that you've invented that contradicts the science/facts because it can't even be reproduced and is therefore effectively impossible!

[1] It is circular logic to claim that "well, yes, there are all sorts of measurable differences, but you're sure none of them individually or in combination, is audible", and then go back to claiming that the measurements show nothing.
[2] So, if there is an audible difference.....
Maybe we haven't measured all of the right things...
Maybe our measurements aren't accurate enough...
Maybe we're wrong about some of those presumed "thresholds of audibility"...
Maybe the difference is due to some error we've made or some external factor we haven't thought of...

Rinse and repeat!

1. It would be circular logic if that's what we were claiming but it's not. Therefore, misrepresentation, bla bla bla. I/We actually claim the exact opposite, the measurements DO in fact show something. Firstly, they will almost always show differences and sometimes they will show that those differences are below or even way, way below audibility!

2. Again, as YOU yourself stipulated, have you reliably "confirmed it's really there", is it really audible? And what do you do next? Go straight to a bunch of nonsense possibilities which contradict science/the facts. And, you didn't even invent them yourself, you're just repeating a bunch of the same old nonsense that the audiophile world has been peddling for decades!

Not TESTING audiophile claims and myths, just rewording and repeating them endlessly with NO testing or reliable evidence whatsoever. Round and round we go, when the audiophile BS will stop nobody knows (although all the indications are "never")!!

G

 

[KeithEmo]

You are absolutely correct.... it is extremely unlikely that a CD will ever play without some errors (probably many errors).
In fact, CD-R and DVD-R media is assumed to have errors, and the quality rating for it specifies the acceptable number of errors-per-second (BER) - among other things.
(Compared to CDs, DVDs have smaller pits, narrower tracks, higher allowable error rates, and even more robust error correction.)

HOWEVER, CDs also have a rather robust error correction mechanism.
A significant amount of extra redundant information is stored on the disc (somewhere around 10% extra for a CD.)
Then, when the CD is played, the data is tested; and, if errors are detected, the extra information is used to correct the errors.
The first two levels of this error correction allow for perfect correction of the data... and these are referred to as correctable errors.
As long as the total amount and number of errors fall below this limit, once the data passes through the error correction algorithms, the errors no longer exist.
(There are no approximations involved... the data that is output is actually 100% perfect.)
(According to the standard, a single gap of up to 2 mm in a single track should be correctable... or a relatively large number of smaller errors... depending on their locations on the disc in relation to each other.)
This error correction is standard for normal Red Book CD readers - so all commercial CD transports, including low cost ones, are supposed to include it.
(Of course, it is possible that some custom designs might omit it, or fail to implement it correctly.)

Then, if and only if the amount of missing data, or the number of errors, exceed the amount which can be corrected, interpolation is used to simply "fill in the gap".
(At this point, we are replacing missing information with guesses, which may well be audible as ticks and pops, or may be audible in other ways as a degradation of the sound.)
For whatever reason, while it is easy to verify perfect data when using a computer player, audio CD players almost never report their error correction status....
(If this information was reported your CD player could include a "perfect data" LED to assure you that no uncorrectable errors had occurred or a "warning" LED to tell you that interpolation type error correction had been required.)

ASSUMING THE ERROR CORRECTION MECHANISM IS PRESENT AND WORKING PROPERLY, missing or misread pits don't matter unless they exceed the maximum number that can be successfully corrected.

Of course, there are several possible exceptions to this:
- The error correction mechanism may NOT be properly implemented on a given CD player.
- It's possible that enough vibration could cause so many data errors that they exceed the maximum number that can be corrected.
- It's possible that vibration could cause more errors to occur when reading a disc that is already dirty or damaged (thus rendering a "borderline" disc as "unreadable".).
- It's possible that, IN A CERTAIN SPECIFIC PLAYER, operation of the error correction mechanism itself could cause other issues.
(For example, it's possible that, if correcting a large number of errors were to consume too much processing power, the EC processor could lose data, or deliver its output data with excessive jitter, or experience some other unforeseen problem.)

As I mentioned above, assuming everything is working as it should, then none of these issues should occur....
(But, then, that is probably not a safe assumption.)
(In the old days, many reviewers included a standard test, to confirm how well the error correction in a given transport actually worked.)

One thing that many people don't realize is that, while audio CDs can play with flaws and interpolated errors....
On a CD-R or DVD-R used for computer data - even a single bad bit which cannot be corrected perfectly will cause an unrecoverable error.
(So the maximum number of uncorrected errors that can be tolerated on a data disc is zero.)

Oops.... - somebody talking theory, without ever recording music ( and by that, I mean REAL music - musicians/room/microphones/some kind of storage ) in real life.

Nope, assuming optical disc playback to be perfect is NOT how it is in real life. Be nice and re-check the size of the CD pits - and then put any of your beloved CDs with hole on any of your fingers that fit into that hole. Flick the rim of the CD with the fingernail of the other arm - close to your ear. You WILL hear the CD vibrating.... - with amplitude exceeding the pit size. Forcing the laser serve to perpetually search for the focus.

Now repeat the same test - this time with the paper that comes in all/any CD-R media on top of the CD-R stack. You WILL hear much less of the CD resonance, both in amplitude and in duration - it is over almost instantly and does not ring like CD normally does. That paper of course can not compare to the effect of the mat - where probably the best is graphite, but so thin graphite disk is brittle to the max and most likely anything but durable. Next best thing - carbon fibre mat. While probably not as good as graphite, with reasonable care it will last in normal 1x speed transports such as CD and DVD player for a lifetime.

Of course, no one is flicking the rim of the CD while playing back - at least not with the magnitude of fingernail. Then again, re-check the size ( depth... ) of the information pits of the CD ... - and then, DVD. It is likely DVD benefits because of this even more than CD. Anything that rotates is bound to vibrate to some extent - no such thing as perfect bearings with zero free play and noise.

CD mat has another advantage - optical. CD-R ( and CD ) media is NOT entirely non permeable for light - just check some different samples looking trough them to a light bulb. Some are at least semi-transparent - and likely to be more or less so, depending on any label printing or graphics - meaning optical conditions are NOT uniform, but are changing according to whatever is on the label. Placing a black carbon fibre mat on top of the label will instantly make this translucence problem ( again, a possible source of forcing laser servo into constant focus correction ) obsolete. For each and every CD in your collection.

Unless you have "turntable type" CD transport - then no mat is required.

 

[analogsurviver]

You are absolutely correct.... it is extremely unlikely that a CD will ever play without some errors (probably many errors).
In fact, CD-R and DVD-R media is assumed to have errors, and the quality rating for it specifies the acceptable number of errors-per-second (BER) - among other things.
(Compared to CDs, DVDs have smaller pits, narrower tracks, higher allowable error rates, and even more robust error correction.)

HOWEVER, CDs also have a rather robust error correction mechanism.
A significant amount of extra redundant information is stored on the disc (somewhere around 10% extra for a CD.)
Then, when the CD is played, the data is tested; and, if errors are detected, the extra information is used to correct the errors.
The first two levels of this error correction allow for perfect correction of the data... and these are referred to as correctable errors.
As long as the total amount and number of errors fall below this limit, once the data passes through the error correction algorithms, the errors no longer exist.
(There are no approximations involved... the data that is output is actually 100% perfect.)
(According to the standard, a single gap of up to 2 mm in a single track should be correctable... or a relatively large number of smaller errors... depending on their locations on the disc in relation to each other.)
This error correction is standard for normal Red Book CD readers - so all commercial CD transports, including low cost ones, are supposed to include it.
(Of course, it is possible that some custom designs might omit it, or fail to implement it correctly.)

Then, if and only if the amount of missing data, or the number of errors, exceed the amount which can be corrected, interpolation is used to simply "fill in the gap".
(At this point, we are replacing missing information with guesses, which may well be audible as ticks and pops, or may be audible in other ways as a degradation of the sound.)
For whatever reason, while it is easy to verify perfect data when using a computer player, audio CD players almost never report their error correction status....
(If this information was reported your CD player could include a "perfect data" LED to assure you that no uncorrectable errors had occurred or a "warning" LED to tell you that interpolation type error correction had been required.)

ASSUMING THE ERROR CORRECTION MECHANISM IS PRESENT AND WORKING PROPERLY, missing or misread pits don't matter unless they exceed the maximum number that can be successfully corrected.

Of course, there are several possible exceptions to this:
- The error correction mechanism may NOT be properly implemented on a given CD player.
- It's possible that enough vibration could cause so many data errors that they exceed the maximum number that can be corrected.
- It's possible that vibration could cause more errors to occur when reading a disc that is already dirty or damaged (thus rendering a "borderline" disc as "unreadable".).
- It's possible that, IN A CERTAIN SPECIFIC PLAYER, operation of the error correction mechanism itself could cause other issues.
(For example, it's possible that, if correcting a large number of errors were to consume too much processing power, the EC processor could lose data, or deliver its output data with excessive jitter, or experience some other unforeseen problem.)

As I mentioned above, assuming everything is working as it should, then none of these issues should occur....
(But, then, that is probably not a safe assumption.)
(In the old days, many reviewers included a standard test, to confirm how well the error correction in a given transport actually worked.)

One thing that many people don't realize is that, while audio CDs can play with flaws and interpolated errors....
On a CD-R or DVD-R used for computer data - even a single bad bit which cannot be corrected perfectly will cause an unrecoverable error.
(So the maximum number of uncorrected errors that can be tolerated on a data disc is zero.)

I should have be more exact in my post - what is actually meant to showcase the benefits of CDmat is RECORDING LIVE MUSIC - directly to CD-R or CD-RW disc.

Here, most of the error correction measures are reduced to the bare minimum - of course, the machine can not buffer in its memory something that has not even happened yet, etc... There is no computer software that can measure data errors in this case - or, at least, not something that has been available and affordable say 15 years ago.

Optical reading/recording is nowhere as "perfect" as some would like lead you to believe. It was a revelation to have find the last few gold CD-Rs from BASF on the shelf in a mall I used to briefly work at - less than 10 pcs, used up in 2 or maybe 3 recording sessions. Then, searching for yet more gold CD-Rs, it turned out that they were, about a decade ago, a dissapearing breed - cost for so called archival media has simply been to much for normal users. There was no denying gold CDs sound better than normal variety - but becoming unavailable - FAST. I have been searching for any "replacement" - archival or anything that might offer similar quality and longeivity. And found I did... - luckily, promo sale of then brand new CD-Rs were also compatible with Philips/Marantz CD-R ( pro ) recorders - which are otherwise quite picky beasts when it comes to media. That hunch/gamble paid off greatly - but it could have also backfired badly; one does not, at least not usually, buy at unseen/unheard/untested - 1000 CD-Rs in a single batch ( 10 boxes with 100 CD-Rs each ). These offered an unmistakable improvement in the sound quality obtainable from CD-R/RW recorders.

As with everything that is overachiever ( offers way too much vs asking price ), this product has been rather quickly terminated - but is, at least to my knowledge, the best CD-R, exceeding even gold variety. The claim was for archival use ( > 100 years ), so far I could not find any problems with by now over a decade old discs - already recorded or still blank.

And then came the CD mat. Again, offering improvement in CD-R/RW recording. Both the mentioned disks and mat have also been used for CD-R burning by computer - with the reservation no spinning above about 4x normal playback of the burner drive takes place - ever.

But, usually, I burn my CD-Rs with SLOWER speed than 1x - Yamaha's AMQR (Audio Master Quality Recording) https://usa.yamaha.com/files/download/brochure/1/320331/CDR-HD1300_U_bro.pdf .
Compared to normal CD-R burning , which allows 80 minute of audio on 700MB disk, AMQR only allows slightly above 63 minutes of audio. Burning 63 minutes of audio takes at "1x" speed slightly below 90 min - IIRC. It has been a while since I last burned a CD-R ...

It has been first available in computer burners - CRW-F1, both in-built and standalone USB version (which has quite good sounding analog RCA out ! ). To this day, these drives will sparkle bidding wars on ebay... particularly the NOS samples.
Properly done AMQR recorded disc will outplay any commercially available CD, even if it has been derived from it (preferably ripped and data verified ) - couple that to both ripping and recording done using CD mat, and it is sure to put smile on your face and raised eyebrows on anyone who has not heard CD in this quality before.

As you can see, standard CD DOES have problems with jitter - at its very source, the disc itself. And that could be far worse a problem than the jitter in the DACs. I know most listen today to RBCD from the CDs ripped to hard drive, that CD players are dying bred, etc.

But the need for stabilization of optical discs in SACD players is still very much there - unless you are willing to fiddle with SACD ripping, which most definitely WILL turn you into an - ebay hawk. The number of old(er) models of Sony Playstation ( before they ripped almost everything supporting SACD out... ) that are indispensable for (unofficial, of course ) ripping of SACDs at home level, available for sale, is ever dwindling - which drives the cost of remaining NOS units ever higher.

 

[KeithEmo]

For anyone interested in RIPPING SACDs......

You are quite correct.... until recently about the only way to RIP SACDs was to modify and hack a PlayStation or actually modify one of a few other SACD players.
HOWEVER, the Oppo 103/105 can also be used to RIP SACDs (that's the last model before the most recent 4k 203/205 version).
Even better, it can be done by booting from special firmware on a USB stick (so you don't have to permanently modify the player).
I've also read that the same method works with one or two other models that use the same chip-set as the Oppo (maybe one or two recent Pioneer models???)

I've never done this.. and I personally have little interest in ripping SACDs.
However, it has been widely reported to work, and seems relatively simple.
You have to make up a special USB stick and boot the Oppo with it...
You then Telnet into the Oppo from any convenient computer and simply issue an instruction to RIP the disc and save the SACD ISO file.
If you Google it, you can find both the instructions, and the free software you need to make it work.
(The nice part is that it makes no permanent modification to the hardware or firmware on the Oppo itself.)

BTW.....

Jitter present on the clock when the original A/D conversion takes place will add permanent distortion to the resulting digital audio data...
(The data itself is affected by both the analog input, the accuracy of the conversion, and the timing accuracy with which the conversion is clocked.)
And jitter present in the data coming off the disc, or while the data is being transmit, can cause mis-reads and data errors at those points...
However, since jitter is a characteristic of the clock, and not the data itself, as long as the data itself is error-free, you can always eliminate jitter simply by re-clocking the data.
(The clock is only used to move data or convert between formats.... and a bad clock can cause data errors.... but the clock itself is not stored with the data. )

Many of the early CD recorders seemed to have various issues with their A/D conversions... and were prone to data dropouts and similar problems.
I had one of the early Marantz "pro" models.
It was very fussy about what type of blanks to use, and often produced flawed or unreadable discs, even if you were careful.
In the early days of separate "audio CD recorders".... , many "consumer" recorders were also restricted to using only "audio" CD-R blanks".
(This was the result of some sort of agreement between the recording industry and the manufacturers of audio CD recorders.)
Certain CD-R blanks were tagged as "audio" CD-R blanks after a royalty was paid to the music industry (they were actually marked as "audio" CD-Rs on the package.)
While a computer would write on any CD-R, "home CD audio recorders" would actually verify the disc, and would only record on CD-R blanks marked for "audio".
(When discs cost several dollars each there was about a 50 cent premium for "audio CD-Rs".)
However, more expensive "professional recorders" had no such restrictions, and would record on any type of CD-R.
In addition to this, many early recorders would only work with certain types of surface dyes (the different colored CDs use different sorts of dyes).
(My Marantz "professional" model worked with the older green 1x discs.... but would not work with the newer silvery ones or the blue dye on Verbatim brand discs.)

I should have be more exact in my post - what is actually meant to showcase the benefits of CDmat is RECORDING LIVE MUSIC - directly to CD-R or CD-RW disc.

Here, most of the error correction measures are reduced to the bare minimum - of course, the machine can not buffer in its memory something that has not even happened yet, etc... There is no computer software that can measure data errors in this case - or, at least, not something that has been available and affordable say 15 years ago.

Optical reading/recording is nowhere as "perfect" as some would like lead you to believe. It was a revelation to have find the last few gold CD-Rs from BASF on the shelf in a mall I used to briefly work at - less than 10 pcs, used up in 2 or maybe 3 recording sessions. Then, searching for yet more gold CD-Rs, it turned out that they were, about a decade ago, a dissapearing breed - cost for so called archival media has simply been to much for normal users. There was no denying gold CDs sound better than normal variety - but becoming unavailable - FAST. I have been searching for any "replacement" - archival or anything that might offer similar quality and longeivity. And found I did... - luckily, promo sale of then brand new CD-Rs were also compatible with Philips/Marantz CD-R ( pro ) recorders - which are otherwise quite picky beasts when it comes to media. That hunch/gamble paid off greatly - but it could have also backfired badly; one does not, at least not usually, buy at unseen/unheard/untested - 1000 CD-Rs in a single batch ( 10 boxes with 100 CD-Rs each ). These offered an unmistakable improvement in the sound quality obtainable from CD-R/RW recorders.

As with everything that is overachiever ( offers way too much vs asking price ), this product has been rather quickly terminated - but is, at least to my knowledge, the best CD-R, exceeding even gold variety. The claim was for archival use ( > 100 years ), so far I could not find any problems with by now over a decade old discs - already recorded or still blank.

And then came the CD mat. Again, offering improvement in CD-R/RW recording. Both the mentioned disks and mat have also been used for CD-R burning by computer - with the reservation no spinning above about 4x normal playback of the burner drive takes place - ever.

But, usually, I burn my CD-Rs with SLOWER speed than 1x - Yamaha's AMQR (Audio Master Quality Recording) https://usa.yamaha.com/files/download/brochure/1/320331/CDR-HD1300_U_bro.pdf .
Compared to normal CD-R burning , which allows 80 minute of audio on 700MB disk, AMQR only allows slightly above 63 minutes of audio. Burning 63 minutes of audio takes at "1x" speed slightly below 90 min - IIRC. It has been a while since I last burned a CD-R ...

It has been first available in computer burners - CRW-F1, both in-built and standalone USB version (which has quite good sounding analog RCA out ! ). To this day, these drives will sparkle bidding wars on ebay... particularly the NOS samples.
Properly done AMQR recorded disc will outplay any commercially available CD, even if it has been derived from it (preferably ripped and data verified ) - couple that to both ripping and recording done using CD mat, and it is sure to put smile on your face and raised eyebrows on anyone who has not heard CD in this quality before.

As you can see, standard CD DOES have problems with jitter - at its very source, the disc itself. And that could be far worse a problem than the jitter in the DACs. I know most listen today to RBCD from the CDs ripped to hard drive, that CD players are dying bred, etc.

But the need for stabilization of optical discs in SACD players is still very much there - unless you are willing to fiddle with SACD ripping, which most definitely WILL turn you into an - ebay hawk. The number of old(er) models of Sony Playstation ( before they ripped almost everything supporting SACD out... ) that are indispensable for (unofficial, of course ) ripping of SACDs at home level, available for sale, is ever dwindling - which drives the cost of remaining NOS units ever higher.