2048/2336/2352/subchannel

vbimport

#1

I found that a lot of CD Image is in 2048/2352 ISO format

From my limited knowledge, the ECC/EDC data is useless in 2352 if the disc is not protected and all ECC/EDC data can be regenerated. I also heard that the SYNC header of each sector is useless. Is my concept correct?

How about the subchannel data? Can the subchannel data be regenerated from the 2048 or 2352 CD Image? If so, can I remove it to save some harddisk space for unprotected cd :slight_smile: ?


#2

> From my limited knowledge, the ECC/EDC data is useless in 2352
> if the disc is not protected and all ECC/EDC data can be regenerated.
> I also heard that the SYNC header of each sector is useless.
> Is my concept correct?

Define ‘useless’.

> How about the subchannel data? Can the subchannel data be regenerated
> from the 2048 or 2352 CD Image?

No.

> If so, can I remove it to save some harddisk space for unprotected cd ?

You cannot remove it, but you could use R-W subchannels to store more
data. You would then have to write your own tool to read these discs.


#3

I think I see what your trying to do, but your wording makes it very ambiguous.

I gather what you really are trying to do is just save space by converting images that have been read at some RAW format (2352 or greater bytes/sector) and reduce them to normal “ISO” 2048 bytes/sector.

If this is what you mean, then you are totally correct, you can do so - providing that the image is not special (ie: protected, twin sectors, etc) in any way.

The extra data would all be regenerated during a standard Mode1 burn, again, providing the original disc the image was read from was also a plain CD-ROM in Mode1.

If you are not absoutely sure, an easy way would be to just burn the RAW image (to a vitual drive for speed) and then re-read it as a .ROM/.ISO file to ensure you don’t screw up.

As you surmised, all header, EDC/ECC and subchannel data is reconstructed when a Mode1 CD-ROM is burnt.

FYI: Your use of the word regenerate is probably what mislead Spath. If you remove such information from the source image, it is impossible to regenerate it if it deviates in any way from what a standard CD-ROM Mode1 image would.

Understand?


#4

Sorry for my bad english and thanks for your answers

The word “regenerate” in my post means “If I convert a 2352 image to 2048 image and the 2048 image is converted back to 2352 format, can I get an identical 2352 image?”

I just wonder if there are any tools that can vertify the image ECC/EDC data.
If all ECC/EDC data is correct, I can safely convert them to 2048 image.

One more basic question, where is the subchannel data stored? Are they stored just next to each sector?


#5

1/. Yes, provding there is nothing abnormal about the original disc.

2/. The easiest way is to just burn the image to a CD-RW and read it back to do a 1:1 compare, if you wish to be 100% certain.

3/. Where on what?

If you mean in the image file: It would generally trail the sector, so you’d have 2352 bytes of RAW sector information and the remainder (2448-2352 or 2368-2352, or whatever format your drives chipset returns) would be the subcode data.

If you mean on the disc itself: If you broke down an EFM frame, which consists of 588 channel bits, the subcode is encoded directly after each sync pattern (of 24 bits) as a single 14 bit EFM codeword.