why are cd-roms with redbook audio split into tracks

[user7]

oic, i'm ripping a cd for the first time in EAC in a week or so. i just put it in three times and got different values for gaps each time lol

[huygens]

That can happen if the cd is scratched. Beyond that make sure your gap detection is set to 'secure' and try the all the gap detection methods (A,B,C) and see if one of the other ones gives better results. If that doesn't help it may be a drive issue.

[user7]

yes indeed it was scratched. greynol from hydrogen audio explained that regardless of what gap time is detected, the final output will be the same. in other words whatever the subchannel data says in relation to gap times, the final output (and checksum) will be the same. at this point i wonder if subchannel data has any relevance at all.

[Jackal]

the gaps determine the individual track sizes..

at this point i wonder if this thread has any relevance at all.

[user7]

maybe this thread doesnt and i'm just failing to understand something, however this is the issue as i see it.

1. different gap sizes can occur for the same cd/cd-rom
2. ripping tracks individually will result in size deviation between multiple rips if gaps deviate (according to Jackals post above), however according to greynol, if gaps deviate, this has NO effect on the end result/checksum (see: http://www.hydrogenaudio.org/forums/ind … opic=72969 )
3. ripping the cd-rom as a single image will not influence size (even if gap sizes deviate), thus are more likely to be correct dumps

maybe i'm just overthinking this or inserting a problem where it is not necessary. i didnt start this thread as a criticism by any means and maybe this issue is only relevant with scratched CDs, however after reading fireball and themabus's 2/3 page argument on subchannel accuracy, i became curious on the effect of mismatching gap size on the accuracy of dumps.

dude, cd-roms are an asspain!

[huygens]

1. different gap sizes can occur for the same cd/cd-rom

Generally no,  fireball and themabus's discussion regards the question of wether an improperly mastered disc with subcode that indicates the wrong gaps should be 'corrected' by rounding to get back the expected pre-mastering tracks. If one of these incorrectly mastered discs is read multiple times it would show the same gaps (just arguably incorrect ones).
This only applies to older systems that had this issue. (i.e. Sega CD).

2. ripping tracks individually will result in size deviation between multiple rips if gaps deviate (according to Jackals post above), however according to greynol, if gaps deviate, this has NO effect on the end result/checksum (see: http://www.hydrogenaudio.org/forums/ind … opic=72969 )

According to greynol in regards to weather CRC with be different:

Depends on what you're telling EAC to do with gaps.

Gaps won't effect track crcs if "No use null samples for CRC calculations" is checked in EAC, so long as the gap isn't so far off as to push data past the track boundary. We want track timing to be correct as well as the track data, so we include the leading and trailing zeros in our Hash calculations. 

3. ripping the cd-rom as a single image will not influence size (even if gap sizes deviate), thus are more likely to be correct dumps

True, but the track timing will deviate resulting in an incorrect gap structure in the cue. In essence the important data on a cd consists of the data and audio tracks and the subcode that indicates track gaps.
Since the subcode can't reliably be dumped with matching crcs we use EAC or other methods to get the track layout and store that information in the cue file. In other words the .cue file captures all the important information from the subcode. Dumping with no gap detection would result in repeatable data and audio track dumps, but we would permanantly lose the subcode information.

[user7]

alright, i think i understand after than explanation. thanks.

edit: i found out that EAC has an option to "securely" detect gaps. it keeps testing them until they get 3 matches