This thread is for discussion of C1/C2 error scans and how to interpret them.
Please begin by reading the media FAQ to get the basics on errors and general media info.
There are several testing utilities around that measure either C2 or both C1 and C2. for this discussion we are using Kprobe, which is designed to work with LiteOn burners. If you have a different burner or reading drive that reports errors in another program, by all means use it. The principles are the same. Please note however than scanning discs in a different drive than they were burned on will introduce additional nuances into the scan results. When using that method, you should give less weight to the actual error counts and focus instead only on the differences between scans.
The point of scanning is to find the combination of media and burn speed that produces the lowest error rates on your burner Each scan that's done for the purposes of comparison should include only one change in the variables. In other words, don't change both the media and the burn speed, don't change both the burn speed and the read speed, change only one thing and scan again to compare results. The point is to get burns with the lowest possible error counts.
The actual error counts are not very important in and of themselves, and comparisons of scans done in different drives is NOT a good idea.
The one and only hard rule with error scans is: less is better. If you lower your burn speed and you get a scan with lower error rates, you are moving in the right direction. If one media has lower counts than another, use that media.
For our purposes, it doesn't make a lot of difference what is being reported as "C1" and "C2" by the drive and the software. All we really need to know is that C1 is the "friendly" error and C2 is the nasty error. All discs show C1 on them in varying amounts, but a good disc should not show any C2. You will see these errors showing in varying colors on the scans that are posted, colors are set by the user and don't mean anything. The C1 and C2 graphs will often be combined into one chart, or may displayed separately in 2 graphs. Please consult the Kprobe thread to learn about how the program works and how errors are displayed. If the charts are combined, the C2 chart will be layed on top of the C1 chart.
You will notice that the scan images you see posted are different than the screen shots in the Kprobe thread. This is because Kprobe saves the basic disc and error info with the image of the scan charts. We are looking here at the saved report from Kprobe. Now let's look at one:
I chose this scan cause it's so pretty, , and because it's a good example of what you do not want to see on a scan.
The first thing to understand about Kprobe is that the graph is auto-scaled, so the errors always fill the graph. You have to look at the scale on the side to know where the max error levels fall. A scan with only max=10 level errors can look the same as one with max=1000 errors, so you have to check.
Along the bottom of the chart, you see relative time measured, indicating the location on the disc. On the left is the start of the disc, (inside of the disc), and on the right is the outside of the disc. (the end). The chart will end (on the right) at the end of the burned portion of the disc, not at the max capacity of the disc.
The error values are also displayed in the top area of the image. You will see the "max", "total" and "average" counts showing there. Max and total are the most important values, the average count is just that, an average of all the error values on the scan. It can be misleading sometimes, so don't fall into the trap of using the average counts as a measure of "quality". A disc can have fairly high average C1 value, and still be a very good burn.
In VERY general terms any C1 average count under 10 might be acceptable, but higher values are not always the end of the world either. But, on CDR's we prefer to see avarage C1 counts under 2, with max counts under 20.
The total error count is more of a measuring stick for comparing one disc to another, but again the actual value is not so important.
Here's another scan that's a bit easier to look at:
As you can see here, there are a few C2 and high C1 values. this disc would be considered "marginal". It's playable and the data is intact, but the scan indicated a problem with the media, the burner, the reader or burn/read speeds. In other words, something needs to change. In this case, it's a RW disc so very little can be done to reduce the error rates other than lowering the read speed. In Windows, most drives will slow the read speed to correct these errors. It's also a disc that should be considered less reliable over time because the errors can degrade to become much worse.
Now let's look at a really good disc:
Note that the max error values are under 10, and total and average counts are also low. This is a disc you can trust. Discs with even 2-3 times these rates are considered "good enough" by most people. A pressed CD will usually have far more errors than this.
The other thing you need to pay attention to when looking at these scans is the scan speed. Speed = more errors. Most people will scan CDR/RW discs at max speed. but if you encounter a disc that has problems, lowering the read speed will make it easier to scan accurately. The read speed is also included on the image near the middle of the top portion.
Be wary of scans that are done at low speeds, as they will almost always show low error rates, and may not tell you much about how the disc will perform outside the scanning program.
The best result for any scan is this:
Full speed scan with low C1 and no C2. Some scanning programs allow the drive to slow, and also display the drive speed during the scan. Look for scans that complete at full speed with no slow-downs.
Error scanning 101:
Error scans are one of the most misunderstood things around in burning circles. People often fail to remember that the media and the burner are only 2 of several variables that effect the outcome of the scan.
You cannot always judge a burner by the error scans, or the media either.
The only truly legitimate use for error scans is to compare different burns in the same drive. In other words, finding the right burn speed, the right media, and the right firmware for your media. Beyond these simple, limited purposes, you are exceeding the limits of the data by drawing any conclusions about the drive quality or media quality.
It's easy to spot a really good disc, and a really crappy one. But most scans will fall somewhere in between where interpretation is more of an art than science. When you get to know your drive and media very well, you know what to expect from them and small differences can be noted easily. However, every scan varies to some extent, so drawing conclusions based on slight differences in scans is not helpful and will ultimately drive you crazy.
There are at least 5 variables that affect the outcome of the error scan.
1) the burning drive
2) the media burned
3) the burn speed
4) the reading drive
5) the reading speed
1) Every drive has a "preference" for the media it likes to burn, which can include different batches of the same media.
2) Every media varies from batch to batch, disc to disc, and even from the start of the disc to the finish.
3) Every burner has a "preference" for burning speed, regardless of what media is in the drive.
4) Every drive has a preferance for what kind of media it likes to read.
5) Every drive has a preference for what speed it likes to read a given media at.
You cannot draw any general conclusions about any particular drive or media type based on a few scans. If you wish to use a particular media, you should try different firmware revisions and burn speeds to "fine tune" your performance if you want the lowest error rates.
Drive firmware revisions, wear and tear, variations from one drive to another, overclocking a drive, and a dozen other factors will affect how it behaves with a given media. Even multiple scans of the exact same CDR can produce varrying results in the same drive.
Another important note: Discs that are "marginal" in burn quality can sometimes exhibit remarkably different scans when scanned multiple times. On one scan, they look OK, the next time the results are very different. On such a disc, lowering the scan speed a notch may resolve the differences between scans.
There is no real evidence to support the conclusion that higher C1 rates (within reason) will adversly impact the performance of a CDR. We do know that lesser quality CDR's with higher C1 rates may tend to degrade over time, but given a good quality CDR (that is burned reasonably well initially), there is rarely any degradation seen. The Cyanine and azo dye types have earned a reputation for greater stability over time, even with higher error rates, but this may be due to the fact that they are better made in general.
The error scans should be viewed as more of a benchmark of the performance of a given disc in a given drive, not as a test of the relative quality of either the drive or the CDR. It's just another piece of information in the bigger picture.