I noticed this earlier.. the only systems where the visible write offset really makes sense are PSX and Dreamcast.. in all the other systems, after correction, the audio doesn't start exactly at the pregap, data gets moved into the next track's pregap, etc..
It would be nice to know if the d8 method gives the same offset correction on these discs, but I suppose it does.. there are propably multiple offset corrections needed, but we can only detect 2 of them (read+write)..
An 'intelligent checksum' would make more sense for these systems imho.. as Eidolon explained back then, you'll be ignoring the offset completely instead of assuming that our method of offset correction is the right one (I have no doubt that it is for PSX and Dreamcast, but I can't be sure about the other systems as a lot of dupe games don't have matching audio).. at least we could verify the integrity of the audio data then WITH matching checksums..
Maybe it would be possible to write an app that can determine the most likely original offset by comparing several dumps, for instance saturn ones? based on the following assumptions:
- No data gets moved outside of the track, unless the data starts exactly at pregap.
- If data gets moved outside of the track with the default offset correction, the amount of bytes outside of the track could indicate the additional offset correction needed (there are several psx discs where the last audio track has audio data up until the last byte.. if these bytes are also the last bytes on the cd, this means no data is cut off and it's a hint on what the proper offset correction should be).
- All tracks on a disc need the same offset correction (is the offset difference on saturn discs the same for all tracks? I remember that with IBM PC this usually isn't the case due to different mastering, different gap sizes etc)... this means that if we want matching audio offsets for all audio tracks, the pregaps should be ignored because the same games (but different system, version, region, etc) sometimes have different gaps?
- It is likely that one or more tracks start exactly at the pregap.
It's clear that offsets DO exist.. and that for PSX and DC they can be used as values to put the audio data back into the original position (usually exactly @ byte 352800 for one or more tracks on the discs).. I'm not sure if our method makes sense on the other systems though.
Are there any discs in the database that were released with multiple write offsets and where correcting both gives identical checksums for both discs (excluding dummy tracks)? Example: Doom for PSX.