Eidolon said:
Ok... I now ripped Monkey Island and Road Avenger eight times:
- using Alcohol 120%
- using UltraISO
- using my Thinkpad's Internal DVD drive (Hitachi-LG GSA-4083N)
- using my external DVD drive (IBM USB2 Multiburner)
Four different rips for each game, four different .BIN files, four different MD5 hashes.
It is normal: 2 drives with diff sample offsets and 2 softwares with different ripping method, see below. And also, it could be scratches cd or one of your drive can't make accurate rip of audio tracks, so you will have some bytes that differ.
Eidolon said:
Something funny happened with Alcohol 120% - the ripped images always have a 2-second "pregap" between the data track and the subsequent audio tracks. UltraISO doesn't produce that gap. Why is that?
As TascoDLX said, some software copy the gap between data and audio track, some don't. UltraISO and CDRwin do NOT copy this gap and instead they write on the .cue file the "PREGAP 02:00:00" line just between the data track and the audio track (see CDROM standard for more info about pregap between different types of tracks). BUT Alcohol rips the gap, so your .bin will be 2*75*2352 = 352800 bytes larger than a .bin created with UltraISO.
Alcohol is not the best ripper (not really because of the gap ripped, but because of some problems on some specific CDROM structure).
Ripping the gap or not, what is the best ? It will depend on which type of CDROM you want to copy. For Saturn and SCD, not ripping the gap is OK, unless you have a drive with a big negative sample offset. In this case, the audio data will begin in the pregap if you rip your cd in bin/cue.
Eidolon said:
One thing I wonder though - shouldnt the audio offset of CD drives be a problem with the real hardware as well? If Sega used different CD drives (or even different firmwares) in the various Sega/Mega CD models, there should be synch issues as well...
No synch problem, as TascoDLX said, we are talking about samples only. 1 sample = 4 bytes, where 1 sector = 2352 bytes = 588 samples = 1/75 second (1 second = 75 sectors = 44100 samples = 176400 bytes).
Don't forget there are also sample offsets due to the press machine used.
About SCD and Saturn discs, some games have been pressed on different machines with the same "master", so for the same game you can have different pressed cds which produce different rips (with the same ripping tools+drives). This is the case for Daytona USA european version for example. A few machines were used by Sega to produce this game. They used the same "master" but as each press machine had its own sample offsets, ripping those CDs will result in different CRCs, despite they come from the same game (but not the same cd).
To have the "id" of the press machine used for the cd, check out the matrix information.
For ex, for Daytona USA EUR, on my db (not updated for a long time), I already have 2 different matrix recorded, so 2 different press machines used:
http://madroms.free.fr/db/index.php?od=330&text=MK_8120050-Daytona-USA-EUR-MK81200-50
If you want a guide to rip your cd, check the one at
www.redump.org I find this is the best guide we can have for ripping game cds, but not really easy to do for a huge amount of cds.
I am waiting for someone who can make a ripper with offset correction and bin/cue raw mode support. I can't rip my 3000+ cds with the redump.org method unless I have 1 year with no other work(s) to do.