What exactly does CD Speed scan disc/quality check measure?

[cfitz]

I am going to take up Erik Deppe (author of CD Speed and new member at CDRLabs - http://www.cdrlabs.com/phpBB/viewtopic.php?t=9191 ) on his kind offer to answer questions about CD Speed.

Erik, there have been a number of questions on CDRLabs regarding exactly what CD Speed measures with its scan disc and CD quality check features. Here is one example of a (somewhat excited) discussion that took place earlier:

http://www.cdrlabs.com/phpBB/viewtopic.php?t=8194

If possible, could you please clear up this issue with definitive answers? Also, could you tell us your take on what constitutes C1 and C2 errors? I don't have any problem with the general nature of C1/C2 errors, but pinning down an exact definition of these terms is something I haven't been able to do:

http://www.cdrlabs.com/phpBB/viewtopic. ... 6820#46820

(The above link is from a discussion about CD Doctor and WSES, but the general nature of the question is the same.)

Finally, there have been rumors that the next version of CD Speed will include the ability to measure C1 and C2 errors (at least on supported drives). Can you confirm or deny this rumor?

Thanks a lot, both for taking the time to answer questions here and for making such nice programs available to us.

cfitz

[ErikDeppe]

Erik, there have been a number of questions on CDRLabs regarding exactly what CD Speed measures with its scan disc and CD quality check features. Here is one example of a (somewhat excited) discussion that took place earlier:

http://www.cdrlabs.com/phpBB/viewtopic.php?t=8194

If possible, could you please clear up this issue with definitive answers? Also, could you tell us your take on what constitutes C1 and C2 errors? I don't have any problem with the general nature of C1/C2 errors, but pinning down an exact definition of these terms is something I haven't been able to do:

http://www.cdrlabs.com/phpBB/viewtopic. ... 6820#46820

(The above link is from a discussion about CD Doctor and WSES, but the general nature of the question is the same.)

CD Speed uses the standard MMC command to retrieve C2 error information.
The explanation in the MMC manual is:
The C2 error, Pointer bits (2 352 bits or 294 bytes) is included in the data stream. There is one bit for each byte in error in the sector (2 352 total).
A more recent version of the MMC specs has the following explanation:
The C2 Errors code provides for the inclusion of fabricated information based upon the results of C2 error correction (on main channel).

So they're not very clear about this.
Basically the drive manufacturer decides which type of C2 error their drive returns.
Most drives activate the C2 bit if the C2 decoder was unable to correct the corresponding byte.
This is the type of errors LiteOn drives are returning.

CD Speed shows these errors as damaged in ScanDisc.
A red block (uncorrectable error) is shown if the drive was unable to read the sector.
For data discs this means that the ECC/EDC failed.
For audio discs it usually means that the disc was so badly damaged that the laser lost track.

The yellow lines in the CD Quality check represent the number of C2 errors per second.

The comment you made in the first thread is very true. The results of such tests should be seen as relative comparison data.

Finally, there have been rumors that the next version of CD Speed will include the ability to measure C1 and C2 errors (at least on supported drives). Can you confirm or deny this rumor?

The upcoming release will indeed include a C1/C2 error test (actually an improved CD Quality Check).
Drive support may be limited in the first version but that should improve in future releases. Most drive manufacturers are very cooperative

[Ian]

The yellow lines in the CD Quality check represent the number of C2 errors per second.

What about the red lines?

btw.. Thanks for sharing that info with everybody. I can't wait for the next version of CD Speed.

[cfitz]

So they're not very clear about this.
Basically the drive manufacturer decides which type of C2 error their drive returns.

I was afraid of that. The lack of a generally accepted, readily available, clear-cut consensus on the definition of these terms was leading me to suspect that there is no such definition, and that usage probably varies by manufacturer.

Most drives activate the C2 bit if the C2 decoder was unable to correct the corresponding byte.
This is the type of errors LiteOn drives are returning.

Interesting. In other words, even a disc that shows no C2 errors (no yellow damaged sectors) as measured by a tool such as CD Speed may have E22 and E12 errors on it since these errors are correctable at the C2 level. I suppose the same probably applies to the C1/C2 errors reported by WSES and CD Doctor, so that a hypothetical disc that showed no C1 errors as measured by these tools might (probably would) still have E21 and E11 errors.

CD Speed shows these errors as damaged in ScanDisc.
A red block (uncorrectable error) is shown if the drive was unable to read the sector.
For data discs this means that the ECC/EDC failed.
For audio discs it usually means that the disc was so badly damaged that the laser lost track.

The yellow lines in the CD Quality check represent the number of C2 errors per second.

Thanks! Those four sentences clear up a lot of confusion.

The comment you made in the first thread is very true. The results of such tests should be seen as relative comparison data.

Then I guess I will try to follow my own advice from here on out...

The upcoming release will indeed include a C1/C2 error test (actually an improved CD Quality Check).
Drive support may be limited in the first version but that should improve in future releases. Most drive manufacturers are very cooperative

Super! I am looking forward to it. If you need a beta tester, I'm happy to oblige...

Thanks for taking the time to answer these questions.

cfitz

P.S. It looks like this is another issue Inertia had a good hold on. I hope he is doing well wherever he is these days.

[spath]

> I was afraid of that. The lack of a generally accepted, readily available,
> clear-cut consensus on the definition of these terms was leading me to
> suspect that there is no such definition, and that usage probably varies
> by manufacturer.

Geee, I cannot believe you still doubt what a Cx error means... it's
like doubting what 'a red car' means just because you cannot find on
the internet a definition stating that 'a red car is a car whose color
is red'. Again, Cx errors are errors occuring at the Cx correction stage,
and each Cx error is either correctable or uncorrectable. Really you
should realize that 'one agreed definition, sometimes misused' is very
different from 'no agreed definition at all'.

One such misuses is precisely in the definition of the C2 pointers feature
in the MMC spec, from which chipsets with bad C2 reports have been
made. At first look the original MMC definition can be interpreted in 5
different ways, so that different chipsets can actually report 5 different
values although they detected and corrected the very same errors.

But despite this lack of clarity, reading the red book and a bit of thinking
let you choose the good one amongst the 5 : these pointers should flag
bytes which are probably wrong after the complete CIRC corrections,
using the method described in the red book (ie what Mediatek does).

[cfitz]

Geee, I cannot believe you still doubt what a Cx error means... it's
like doubting what 'a red car' means just because you cannot find on
the internet a definition stating that 'a red car is a car whose color
is red'. Again, Cx errors are errors occuring at the Cx correction stage,
and each Cx error is either correctable or uncorrectable. Really you
should realize that 'one agreed definition, sometimes misused' is very
different from 'no agreed definition at all'.

You'll have to forgive me if I don't simply accept your assertions as divine truth, and instead look to find information from other sources as well.

As for your analogy, it is vastly oversimplified. A more accurate, but still imperfect, analogy is that there are some people who say a "red car" is one with a red exterior, while others say a "red car" is one with a red interior, and yet another group insists that the only true "red car" is one that has both a red exterior and interior. In such a situation, there would appear to be no agreed upon standard for "red car".

Look, I've already acknowledged in other discussions with you that your definition is completely reasonable and may represent the correct usage. But there are other definitions that can be argued are just as reasonable. And everyone seems to agree that different manufacturers and developers use the terms differently. You yourself have asked on these forums what CD Doctor means by C1 and C2 errors, implicitly acknowledging that the usage of the terms is not standardized. So I don't know why you find it so hard to believe that I question what the "standard" meaning is, and if such a standard exists at all.

I have never been able to find an authoritative source that confirms any definition, including yours, and you've never offered one, despite my requests that you do so. And no, I don't accept your word alone as an authoritative source. That doesn't mean that I disrespect you or that I think you are wrong or stupid. It just means that in the absence of supporting documentation, your words are just one reasonable opinion among several. I'm looking forward to you producing authoritative documentation, but until you do so, or I find something on my own, the question will remain open in my mind. You are welcome to be frustrated by my attitude if it bothers you, but being condescendingly insulting towards me won't change it.

At first look the original MMC definition can be interpreted in 5
different ways, so that different chipsets can actually report 5 different
values although they detected and corrected the very same errors.

Precisely my point:

usage probably varies by manufacturer.

As far as I am concerned, this is the end of our discussions on this point, until you have new information to contribute. I'm not going to waste my time by engaging in senseless displays of techno-machismo with you.

In the meantime, I will continue to make good use of programs such as CD Speed, WSES and CD Doctor, obtaining useful comparisons of relative burn quality.

cfitz

[spath]

> You'll forgive me if I don't simply accept your
> assertions as divine truth, and instead look to find
> information from other sources as well.

I'm not surprised that you don't trust me, but I'm
surprised that you have not been able to find any
information on this in a month time. If I had doubts
like yours, I would have downloaded and studied all
documents and specs, I would have asked manufacturers
and technical writers, I would have browsed every
newsgroups and boards on the internet. And within
a week I would have found the truth. But be honest,
you're just pretty comfortable with the idea that
there's no standard definition and you never tried
really hard to find out the truth, did you ?

You should realize that if you don't make any effort
to get informations and at the same time you don't
trust people who have these informations, then you'll
stay in doubt on a lot of subjects. But if one day
you read the red book and finally understand what a
C2 error is, then make sure to check chapter 4 of
the part about error correction ; there they explain
how 4 errors can be corrected at C2 stage, so this
should clear another of your doubts.

[Ian]

Please take this pissing match else where.

This was a discussion about CD Speed and what kind of errors it was returning. Please stick to the topic.

[HazMat]

Erik, will there be support for C1 error test on ASUS drives in the next release? Thanks.

[Guzo]

at spinning the drive (very beginning) it always report errors (cd speed)
but if i spin up the drive it doesn't report any error.

Could you give me explanation?

thanx

[rdgrimes]

So they're not very clear about this.
Basically the drive manufacturer decides which type of C2 error their drive returns.
Most drives activate the C2 bit if the C2 decoder was unable to correct the corresponding byte.

If I understand this correctly, then the "testing" programs are simply counting the flagged bytes. This makes perfect sense, but what is interesting is the apparently consistant differences between WSES, CD Dr., and CDSpeed when measuring the same disc on the same drive. CD Dr, for example appears to start indicating C2 errors when the C1 rate reaches a certain point, while WSES does not. I've also seen CD Dr. and WSES fail to report any C2 on a disc where CDSpeed consistantly does report C2. So there must be more to this than just what the drive reports, the program must be interpreting to some degree.

[KCK]

It might help if ErikDeppe told us the precise name of the MMC command issued by CD Speed, and which MMC specs he was referring to. (I guess the majority of recent burners are expected to be at least MMC-2 compliant, but I am not sure about MMC-3.) Then perhaps cfitz could ask the author of CD Doctor whether he uses the same command.

[lppnet]

I've also seen CD Dr. and WSES fail to report any C2 on a disc where CDSpeed consistantly does report C2.

I also experienced this once. The Mitsui Gold that I burned in 24x didn't shows any c2 error (but very high c1 average) in CD Doctor but it shows 2 yellow blok in CDSpeed.

[ErikDeppe]

The yellow lines in the CD Quality check represent the number of C2 errors per second.

What about the red lines?

Similar to the red (unreadable) blocks in the ScanDisc function the red lines in the CD Quality test show that the drive was unable to read the sector.

[ErikDeppe]

Erik, will there be support for C1 error test on ASUS drives in the next release? Thanks.

At the moment Asus drives are not supported.
However, Asus did show some interest in such a test when it was first mentioned to them so I will try to get some feedback from them.
Support from the manufacturers is needed because C1 errors can only be retrieved by using vendor-specific commands.

[ErikDeppe]

at spinning the drive (very beginning) it always report errors (cd speed)
but if i spin up the drive it doesn't report any error.

Could you give me explanation?

thanx

Some drives have this feature (bug actually).
The errors are real so the drive is not just reporting the errors incorrectly.
This shouldn't matter too much for data discs but if you're extracting audio it is recommended to make sure the drive is running at full speed when you start the extraction.

[spath]

> It might help if ErikDeppe told us the precise name of the MMC
> command issued by CD Speed, and which MMC specs he was referring to.

CDSpeed use READCD (0xBE) commands with C2 Error Block
Data as error field. This is the only standard command to get C2
informations, so you don't really have any choice

> Then perhaps cfitz could ask the author of CD Doctor
> whether he uses the same command.

CDDoctor/WSES use proprietary commands, this is different.

[ErikDeppe]

@ KCK, spath

CD Speed indeed uses the Read CD command to get the C2 error information from MMC compatible drives Some non-MMC compatible drives (all Plextor CD-ROM drives for example) are also supported.
I was referring to the MMC-3 and 4 specifications.

@ rdgrimes, lppnet

I've also noticed this with CD Speed. I'll have to check this because this is a bit weird.


C2 errors measured with standard MMC command


C1/C2 errors measured with vendor-specific command

[HazMat]

Today I bought a 10-pack of Delphi 24x branded disks (ATIP says "Fornet International" - never heard of them, probably crap). After I burned the first disk at its rated speed (24x) on my Asus CRW4816 I did a Disk Quality Check with CDSpeed v1.02, as I do every time I buy a batch of new disks - the results indicated just short of a coaster - thousands of C2 errors, with a peak around minute 10, after which the drive dramatically slowed down and read the remainder of the CD with less errors (but still there were some). After that, I tested the same CD in my Asus CD-S500, a drive that (based only on CDSpeed Disk Quality Check) seems to be a better reader than the CRW4816. To my surprise, the disk showed even more errors, with a red line at minute 10. So far, so "good".
Hours later I visited a friend and used his TEAC 40x burner to check the bad disk, to see how it shows up. His drive just blasted full speed ahead, no errors and no slowdown (same version CDSpeed). I thought to myself "crap Asus???" No wait, here comes the best part:
When I returned home, I tested again the "bad" CD: only 35 errors with the CRW4816, none at minute 10, and no errors (zero) with the CD-S500, both drives read the CD at full speed... Can anyone explain this behaviour?
Great, isn't it? After being scared from the initial test, I burned the other CDs in the pack at 12x, to make sure they'll be readable...

[jase]

So they're not very clear about this.
Basically the drive manufacturer decides which type of C2 error their drive returns.
Most drives activate the C2 bit if the C2 decoder was unable to correct the corresponding byte.

If I understand this correctly, then the "testing" programs are simply counting the flagged bytes. This makes perfect sense, but what is interesting is the apparently consistant differences between WSES, CD Dr., and CDSpeed when measuring the same disc on the same drive. CD Dr, for example appears to start indicating C2 errors when the C1 rate reaches a certain point, while WSES does not. I've also seen CD Dr. and WSES fail to report any C2 on a disc where CDSpeed consistantly does report C2. So there must be more to this than just what the drive reports, the program must be interpreting to some degree.

The LiteOn drives seem to use a special mode when "counting" C1 errors, which could explain the discrepancy between CDD/WSES and CDS.

I'm interested to know people's opinion on the following: If a certain disc can't be read at 52x and CDD reports C2 errors toward the end of the disc, but at 8x the disc reads through fine with very low C1 error count (an example at http://jasejames.tripod.com/ritek.htm) can we say that disc has C2 errors? If you spin any disc fast enough you can coax errors out of the reading process (those errors are probably due to bad disc balancing and/or low laser power meaning fast reading is impossible). So I'd say these errors people witness are actually probably not true C2 errors at all. So surely in order to get a true idea of how many C1/2 errors are on a disc you need to read at 1x?

Fornet? Eurgh. They still around?

[rdgrimes]

Consider that you're measuring "read-errors", not "disc errors", and it makes sense. An error is an error in that sense. So it doesn't matter what causes it , the drive is reporting the error, so it occurred. The condition of the disc is one of the factors that contributes to those errors, read speed is another, the "quality" of the drive is another.

[dodecahedron]

So surely in order to get a true idea of how many C1/2 errors are on a disc you need to read at 1x?

makes a lot of sense to me.
that way we're really checking "disc errors" and not "read errors".

[spath]

> I'm interested to know people's opinion on the following: If a
> certain disc can't be read at 52x and CDD reports C2 errors
> toward the end of the disc, but at 8x the disc reads through
> fine with very low C1 error count (an example at
> http://jasejames.tripod.com/ritek.htm) can we say that disc
> has C2 errors?

No, you just cannot say that a disc has C1 or C2 errors : a disc
has physical properties/defects, which can cause C1/C2 errors
to be detected by the CIRC. But these errors depend on a lot
of parameters including the rotating speed, the brand of the
drive, its firmware, etc. In the end C1/C2 measures at low
and high speed are both valid, it just depends on what you
want to test.

[jase]

> I'm interested to know people's opinion on the following: If a
> certain disc can't be read at 52x and CDD reports C2 errors
> toward the end of the disc, but at 8x the disc reads through
> fine with very low C1 error count (an example at
> http://jasejames.tripod.com/ritek.htm) can we say that disc
> has C2 errors?

No, you just cannot say that a disc has C1 or C2 errors : a disc
has physical properties/defects, which can cause C1/C2 errors
to be detected by the CIRC. But these errors depend on a lot
of parameters including the rotating speed, the brand of the
drive, its firmware, etc. In the end C1/C2 measures at low
and high speed are both valid, it just depends on what you
want to test.

OK, therefore we arrive at the following conclusion: To say "brand X when written at Y speed on brand Z writer caused N C1 errors, this is therefore a bad burn" is actually an erroneous statement. A C1 error count for a certain type of media actually tells us very little about the state of the recorded media on its own, and should not be used as a black and white argument that brand X doesn't work well with writer Z. True?

[jase]

Today I bought a 10-pack of Delphi 24x branded disks (ATIP says "Fornet International" - never heard of them, probably crap). After I burned the first disk at its rated speed (24x) on my Asus CRW4816 I did a Disk Quality Check with CDSpeed v1.02, as I do every time I buy a batch of new disks - the results indicated just short of a coaster - thousands of C2 errors, with a peak around minute 10, after which the drive dramatically slowed down and read the remainder of the CD with less errors (but still there were some). After that, I tested the same CD in my Asus CD-S500, a drive that (based only on CDSpeed Disk Quality Check) seems to be a better reader than the CRW4816. To my surprise, the disk showed even more errors, with a red line at minute 10. So far, so "good".
Hours later I visited a friend and used his TEAC 40x burner to check the bad disk, to see how it shows up. His drive just blasted full speed ahead, no errors and no slowdown (same version CDSpeed). I thought to myself "crap Asus???" No wait, here comes the best part:
When I returned home, I tested again the "bad" CD: only 35 errors with the CRW4816, none at minute 10, and no errors (zero) with the CD-S500, both drives read the CD at full speed... Can anyone explain this behaviour?
Great, isn't it? After being scared from the initial test, I burned the other CDs in the pack at 12x, to make sure they'll be readable...

Possibly slight warping caused by the media being very warm when you test-read it? TBH I'm not sure. Fornet media is dodgy at the best of times. I had one batch in 2000 which was some of the best budget media I've ever used (all 100 discs still perfect, with low C1 error count -- about 0.6 average when read on a LiteOn at 52x) but other discs from them have been abominations!