Spots on Bottom on DVD-R burned disc

[Terra]

Hey,
I just burned a DVD-R (this one is double sided but this has happened on ACCU single sided as well) and i noticed on the bottom in the burned area that there is like 5 little speaks that are still the original color spread around the burned area. I was just wondering what this means, should i throw the disc away. The data ripped fine w/ DVD dycryptor. I dont want to watch it because it is the end of a series I am only halfway through. Suggestions? Thanks!

[BJ_M]

watch it and see what happens ..

often caused by dust on the disk when burning - but other things can cause it .

[Sartori]

Read this , does this look like it ?


http://www.cdfreaks.com/news2.php3?ID=5612

[Terra]

It was probably dust or something but is the disk bad or not?

[BJ_M]

well see if plays ok is best test

[ultima16888]

It's caused by dust.. i get those often too... optical media are as stated "OPTICAL" sensitive.. anything on disc surface that will cause lazer to not focuz directly where it is suppose to will cause this... go to office depot and buy those canned air ... and blow the dust off when u see them.. don't wipe with anything it gets worse.

[furball6969]

This is why I ALWAYS use an air duster and verify data after the disc is burned.

[defense]

I've noticed this problem on some of my ACCU disks made by Lead Data and Sony and when I've played the disks, they played perfectly all the way through, so it obviously doesn't seem to affect the disk. I have never had as many as "FIVE" spots though, only between 1 and 3.

[defense]

Just to update this post, I want to say that out of ALL of the disks that I have burned, only two seem to have any form of spots such as the ones originally mentioned in this thread. Both of them play flawlessly. Interestingly, one of the burned disks which is an ACCU "lead data" is the movie Bourne Identity. What is more interesting is that there are a total of "four" tiny spots, the same color as the dye (purple) and they are all bunched together. When I play the disk from beginning to end, there is absolutely NO problems. I'm wondering how that can be. I would figure that four spots bunched together like that, would make for some type of skipping or pausing, but there is absolutely no problems ANYWHERE. I am obviously very happy about that, and I now use a can of canned air to spray excess dust from my blank media. If someone would just explain to me how it is possible to have those burn spots on a disk like I have, and not have a single playback issue, I would appreciate it. Thanks

[Faustus]

I've had that a few times with my Riteks, but haven't noticed any problem yet. Doesn't mean there are none, just none that I've noticed. Test it all the way through if it makes you nervous.

[defense]

I did test mine all the way through and they play perfectly from beginning to end. I'm just wondering HOW though. I mean I am obviously happy there are no problems, but I just can't see how there can be four little burn spots bunched together, but I get absolutely NO playback issues or any other issues for that matter. I'm hoping someone will come by that can explain HOW that is possible.

[BJ_M]

ECC and oversampling to the rescue

[defense]

@ BJ_M, if your response was directed to my question as to "HOW" I don't have playback issues with those burn spots on one or two of my disks, I will just ask if you wouldn't mind briefly elaborating on your response. I know you keep your posts short and sweet, but if you wouldn't mind elaborating on exactly what ECC is and oversampling, then explaining how that corresponds to not having playback issues with those burn spots, I would appreciate it. Thanks in advance

[BJ_M]

sometimes i have pretty long responses - i'll give you a little detail on ECC first ..

in short:

ECC = Reed-Solomon Error correction Code , ECC corrects errors on the fly by rewriting the blocks within the same track.

in depth:

Errors are inevitable but by means of robust error correction systems, CD and DVD can have uncorrectable error rates as low as that specified for computers, i.e., 10-12 (one uncorrectable error in one trillion). Audio applications do not require this degree of accuracy.

Sources of error: Include dropouts from the media (oxide wear, fingerprints, scratches), signal degradation (reflection, intersymbol interference, impedance mismatches, RF interference).

Measures of error: The burst length is the maximum number of adjacent erroneous bits that can be fully corrected. The bit-error rate BER is the number of error bits per total bits. Optical disk systems can handle BERs of 1:100000 to 1:10000. The block error rate BLER is the rate of block or frames per second having at least one incorrect bit. The burst error length BEL is the number of consecutive blocks in error.

Methods of correction: Goal is to introduce redundancy to permit validity checking and error detection, error correction code ECC to replace errors with calculated valid data, and error concealment to substitute approximate data for uncorrectable invalid data. Redundancy includes repeating the data, adding single-bit parity bits (to check if odd or even), checksums (e.g., weighted checksums computed modulo 11), and cyclic redundancy check code CRCC.

CRCC uses a parity check word obtained by dividing a k-bit data block by a fixed number (generation polynomial g) and appended to the data block to creat the transmission polynomial v. When the data u is received, it is divided by the same g, and the result subtracted from the original checksum to yield the syndrome c: a zero sydrome indicates no error. Error correction can be accomplished using mathematical manipulation and modulo arithmetic ... Polynomial notation is the standard terminology in the field: e.g., the fixed number 1001011 (MSB leading) is represented as 1x26 + 0x25 + 0x24 + 1x23 + 0x22 + 1x21 + 1x20 or 26 + 23+ 21 + 20. CRCC is typically used as an error pointer and other methods are used for correction.

Error correction techniques employ block codes having row and column parity (CRCC are a subclass of linear block codes), convolutional or recurrent codes (which introduce a delay), and interleaving including cross-interleaving.

Reed-Solomon R-S codes (Irving Reed and Gustave Solomon 1960) employ polynomials derived from Galois fields to encode and decode block data. They are a subclass of q-ary BCH codes which are a subclass of Hamming codes . They are especially effective in correcting burst errors and are widely used in audio, CD, DAT, DVD, direct broadcast satellite, and other apps. Cross-Interleave Reed-Solomon Code CIRC is used in CDs. It includes the use of C2 then C1 encoders (C1 then C2 on decoding). The C1 level of CIRC is meant to correct small, random errors. The C2 level corrects larger errors and burst errors. Interleaving is used between the C2 (28,24) and C1 (32,28) encoders and deinterleaving is needed on decoding. (28, 24) means 28*8 bits are output for the original 24*8 bit input and the final output is 32 8-bit words of which 8 are for "parity" and 24 are actual data. The cross-interleaving stores one C2 word in 28 different blocks spanning a distance of 109 blocks using delay lines etc., crossing the data array in two directions (thus "cross"). With audio CDs, CIRC can correct burst errors up to 3874 consecutive erroneous bits or symbols (2.5 mm track length) and can well conceal 13,282 error bits (8.7 mm) and marginally conceal 15,500 bits. The CD standard requires a block error rate BLER [the number of data blocks that have any bad symbols at the initial C1 error correction stage] of less than 220 per second averaged over 10 seconds (50 would be typical). There are 7350 blocks/sec on a CD (a block or frame, derived from 24x8=192 bits input data, is 32x8=256 bits output to modulator). The resulting CD data rate = 1.4112 Mbps (input data rate, not including parity bits added by CIRC and EFM).so the maximum Redbook BLER of 220/sec (averaged over 10 sec) allows 3% of the blocks to be erroneous. E12 is the rate of single symbol errors at the C2 encoder, which are correctable. E22 expresses the rate of double symbol errors at the C2 encoder--these are the worst but still correctable errors [the first number is always the number of errors and the second number is always the decoder level]. E32 errors are triple bit errors at C2 and are uncorrectable and require interpolation--they should not appear in a new CD and are unacceptable in a CD-ROM. Other measures of error are the E11, E21, E31. The burst error count BST combines E21 & E22 and expresses the number of consecutive C2 block errors that occur in excess of a threshold value such as 7. A new CD might typically have a raw bit error rate of 1E-5 to 1E-6, BLER = 5, E11 = 5, E22 = 0 and E31 = 0 and should never have E32 uncorrectable errors. Digital audio data can be copied with high reliability.

Error concealment includes interpolation (may be low or high order, zero order simply holds the last good value) and muting.

The above info is from my own knowlage and from "Principles of Digital Audio", by Ken C. Pohlmann <--- good book, good reading .


i'll cover oversampling later ..

[defense]

@ BJ_M...WHOAAAA! Where's my bottle of extra strength tylenol when I need it! LOL.....I felt like I was back in one of my statistics classes, but I asked for it. LOL...Actually, ONE thing of the MANY that I love about this site/forum is that I learn something new every day. I think that is very important. I love to learn, and to learn something new, whether simple or complex, is just fulfillment. It feels great to know that i'm learning probably A FEW new things every day on here. And although I didn't know a thing two months ago about any BACK UP methods, I can honestly say that I have a very good understanding of SVCD's and DVD's. I can also honestly say that believe it or not, I actually understood a FAIR amount of the post you have just written. I think you did an amazing job explaning it, even if some points were taken from Pohlmann's "Principles of Digital Audio." I am printing this post so that I can go over it several times. I want to be able to have a greater understanding of the WHY as opposed to just being complaisant with the fact that it works. Thanks once again for that very detailed, and VERY helpful post. When you get around to it, I would like to read what you have to say with respect to oversampling. Thanks