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Are all 32 pre-gap frames equal?, Doing experiments to verify old rips...
krafty
post Sep 10 2012, 16:39
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In the past I have ripped some old CDs which have a pre-gap of 32 frames before the first track. Ripped as tracks, and the pre-gap was left out (And can't verify the rip anymore against AR).

I found out that making a sum of this gap, extracted from any CD that has this gap, plus the "rest" of the rip in the form of image, will give me the exact full image ripped, that had those samples discarded from the initial rip.

But I also found that this can work with any other CD that has the same 32 frames pre-gap, using the same gap file. And the same goes for other gaps such as 33 frames. To the point that I can recreate old rips in its "full entirety" to be checked against AccurateRip without having to rerip all over again.

The question is rather subjective, but are these pre-gaps all binary identical by convention or will they differ as in data sound depending on the "rare" CD with that....?

This post has been edited by krafty: Sep 10 2012, 16:41
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mjb2006
post Sep 10 2012, 16:59
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The track 01 pre-gap is usually all zeroes (digital silence), but IIRC I've seen it instead sometimes be very quiet noise, so I wouldn't assume anything.

AccurateRip checksums don't include the track 01 pregap, nor the first ~5 frames of track 01, nor the last 5 frames of the last track...
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greynol
post Sep 10 2012, 17:00
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As far as AR is concerned that data only serves to offset the start points of each of the tracks. The data in the pregap has no bearing on the checksums in the database whatsoever.


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krafty
post Sep 10 2012, 17:09
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Say that you use foobar2000 to do: rip to multitrack. It will preserve the pre-gap.
If you rip track-based, it will discard the pre-gap.

The multitrack rip will be straight "accuraterippable"...
The second one might not be, it will depend on the database and calculations (as if you check your rip straight off the files only).
CDs without a pre-gap are "accuraterippable" just like the multitrack rips.

What I am saying is that if you get this pre-gap in a file, and join with the track-based rip, you will get the result as if you have ripped multitrack.
The interesting thing is that most 32 gaps are just the same so you can re-create full multi-track rips with that one missing gap.

I just found a 32 gap which was not the same as other identical I used to recreate 5 rips.
So the mileage may vary.

This post has been edited by krafty: Sep 10 2012, 17:11
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greynol
post Sep 10 2012, 17:14
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Generate a proper EAC-style cue sheet and use CueTools so you won't have to go through these contortions and possibly mislead yourself into thinking you have a correctly exteacted HTOA when you really don't. smile.gif

This post has been edited by greynol: Sep 10 2012, 17:25


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jayess
post Sep 10 2012, 17:29
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QUOTE (greynol @ Sep 10 2012, 11:14) *
Generate a proper EAC-style cue sheet and use CueTools so you won't have to go through these contortions and possibly mislead yourself into thinking you have a correctly exteacted HTOA when you really don't. smile.gif


Hopefully it's helpful, but although I rip with DbPoweramp, when I later play something, I create a CueTools cue sheet in the rip folder of each album so I know I've done that CD, then run the verify function of CueTools so the CTDB gets populated with the data as well.

I recommend others do the same.

This post has been edited by jayess: Sep 10 2012, 17:31
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greynol
post Sep 10 2012, 17:32
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I guess it doesn't do any harm but you risk creating entries based on false pressings for the very same reason that led to the creation of this topic. These entries will not help those who are trying to verify legitimate pressings which have been ripped and indexed in such a way as to preserve this legitimacy.

This post has been edited by greynol: Sep 10 2012, 17:38


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jayess
post Sep 10 2012, 17:38
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QUOTE (greynol @ Sep 10 2012, 11:32) *
I guess it doesn't do any harm but you risk creating entries based on false pressings for the very same reason that led to the creation of this topic.


I keep the box unchecked not to ask again if I want to submit the data to CueTools and I've found that it only asks for me to submit probably 1 for every 15-20 CD's that I have it verify. So it appears pretty selective with the data.
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korth
post Sep 10 2012, 18:17
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CUETools will only submit if AR confidence is greater than or equal to 2 AND there is no CTDB submission for that disc.

This post has been edited by korth: Sep 10 2012, 18:26


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greynol
post Sep 10 2012, 18:28
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I remember the first half of that which was >2 (when did it change?), though my recent involvement in that discussion really wasn't adequately addressed when it could have been:
http://www.hydrogenaudio.org/forums/index....st&p=806131

I really can't blame anybody but myself, though.

This post has been edited by greynol: Sep 10 2012, 22:07


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krafty
post Sep 10 2012, 18:48
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I would like to say that the process of checking with AR which I am using is only through foobar2000. It's just a trick to reconstruct a multi-track rip off foobar2000 if you don't feel like re-ripping or no longer have a DVD-RW drive. I haven't used cuetools in a long time and last time I checked it was version 2.x which was pretty unusable to me. It's true that you can miss HTOA, but it's not the case with most pressings. The AccurateRip is only a plus. You can check your own previous rip integrity by just checking the CRC32 image.
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