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Different start position of pre-track gap detected by different disc drives


Martin N
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Hello;

 

I would be very grateful for any suggestions that would help me to explain, and eliminate, the following discrepancies in CUE information regarding the pre-track gap preceding Track 8.

 

During some experimenting I converted the same Audio CD into image files using Exact Audio Copy (EAC) and ImgBurn with four different disc drives: GCR-8523B (CD-ROM), GDR-H30N (DVD-ROM), GDR-8162B (DVD-ROM), and ND-3540A (DVD-RW). As can be seen below, CUE information generated by EAC is the same for all four drives (in terms of the duration of Track 7 and 8).

 

However, ImgBurn detected the pre-track gap differently in two of the drives: Whereas GCR-8523B and GDR-H30N values were identical (within a frame) to EAC, GDR-8162B and ND-3540A detected pre-track gap that starts sooner by 15 frames, therefore correspondingly shortening Track 7 and extending Track 8.

 

I am not sure if this is relevant, but GCR-8523B and GDR-H30N are on one computer, and GDR-8162B and ND-3540A on another, but both machines run the same operating system and the same version of ImgBurn and EAC.

 

Thanks!

 

GCR-8523B

 

ImgBurn CUE

...

TRACK 07 AUDIO

INDEX 01 34:28:15

TRACK 08 AUDIO

INDEX 01 38:33:15

 

EAC CUE

...

TRACK 07 AUDIO

TITLE "Track07"

PERFORMER "Unknown Artist"

INDEX 01 34:28:15

TRACK 08 AUDIO

TITLE "Track08"

PERFORMER "Unknown Artist"

INDEX 01 38:33:15

 

GDR-H30N

 

ImgBurn CUE

...

TRACK 07 AUDIO

INDEX 01 34:28:15

TRACK 08 AUDIO

INDEX 00 38:31:69

INDEX 01 38:33:15

 

EAC CUE

...

TRACK 07 AUDIO

TITLE "Track07"

PERFORMER "Unknown Artist"

INDEX 01 34:28:15

TRACK 08 AUDIO

TITLE "Track08"

PERFORMER "Unknown Artist"

INDEX 00 38:31:70

INDEX 01 38:33:15

 

GDR-8162B

 

ImgBurn CUE

...

TRACK 07 AUDIO

INDEX 01 34:28:15

TRACK 08 AUDIO

INDEX 00 38:31:54

INDEX 01 38:33:00

 

EAC CUE

...

TRACK 07 AUDIO

TITLE "Track07"

PERFORMER "Unknown Artist"

INDEX 01 34:28:15

TRACK 08 AUDIO

TITLE "Track08"

PERFORMER "Unknown Artist"

INDEX 00 38:31:70

INDEX 01 38:33:15

 

ND-3540A

 

ImgBurn CUE

...

TRACK 07 AUDIO

INDEX 01 34:28:15

TRACK 08 AUDIO

INDEX 00 38:31:54

INDEX 01 38:33:00

 

EAC CUE

...

TRACK 07 AUDIO

TITLE "Track07"

PERFORMER "Unknown Artist"

INDEX 01 34:28:15

TRACK 08 AUDIO

TITLE "Track08"

PERFORMER "Unknown Artist"

INDEX 00 38:31:70

INDEX 01 38:33:15

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EAC has been doing what it does for years, ImgBurn is no where near as mature/accurate for audio stuff.

 

The 'GCR-8523B' is just useless - period.

 

It's unlikely you'd notice 15/75th's of a second difference (of what's probably just 'silence') so just use whatever you're comfortable with.

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EAC has been doing what it does for years, ImgBurn is no where near as mature/accurate for audio stuff.

 

The 'GCR-8523B' is just useless - period.

 

It's unlikely you'd notice 15/75th's of a second difference (of what's probably just 'silence') so just use whatever you're comfortable with.

 

Hi LUK!

 

I understand that pre-track gap may be subject to some variability, as it is being detected from sub-channel Q-data. However, I thought that the start time/sector of a track should be taken from the TOC in the lead-in area, which is fixed. Even GCR-8523B gets it right... I looked at the disc in ND-3540A using CDTool, and the TOC entry for Track 8 conforms to EAC (starting LBA 173490) not ImgBurn (starting LBA 173475), although ImgBurn track information indicates LBA 173490.

 

Thanks!

post-21577-125738108339.jpg

post-21577-125738110086.jpg

post-21577-125738111053.jpg

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My TOC info is read from the drive and displayed verbatim.

 

So what you're seeing there in the disc info panel is what the drive has reported.

 

I query the Raw TOC, CDTool queries the Formatted TOC (by default anyway - change 'Read TOC format' to 'All TOC info' to make it read Raw TOC). I expect that's where the difference is coming from.

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I query the Raw TOC, CDTool queries the Formatted TOC (by default anyway - change 'Read TOC format' to 'All TOC info' to make it read Raw TOC). I expect that's where the difference is coming from.

 

You were correct, LUK! In the raw mode, CDTool and ImgBurn reported the same thing on ND-3540A. Why would formatted and raw mode reading of TOC differ? Is the formatted form not just an interpretation of the raw data? I apologize if my ignorance is showing :)

 

On another note, I removed GDR-H30N, which behaves "correctly" on machine A (i.e. raw and formatted TOC info is the same), and tried it in machine B, which is normally equipped with ND-3540A. To my surprise, GDR-H30N started to behave "incorrectly" (i.e. raw and formatted info is NOT the same). Knowing the nuts and bolts of disc drive reading/writing, can you suggest which aspect of the hardware/operating system could be responsible for the difference?

 

Thanks again for continuing this discussion with me - I am a bit unsettled by this apparent dependence of disc drive performance on the host computer system.

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To be honest, I've never seen one where Formatted is different to Raw. Then again, my program always shows Raw where possible and falls back to Formatted when it's not available (as is the case with DVD/HD DVD/Blu-ray) - so I wouldn't have ever noticed it anyway.

 

Oh and yes, you'd expect Formatted to be an interpretation (slightly cleaner looking version) of Raw data but I guess that's not always the case!

 

Perhaps the 'Formatted' info uses something from the 'Track Information' to make up it's numbers... I really have no idea! The only people that could answer that question are the ones programming the firmware in the drive.

 

I would have assumed all this stuff came directly from the drive so moving it between computers shouldn't have made any difference. It's very weird if you're saying it did - perhaps some filter driver is messing things up?

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Thank you for the lightning-fast response! :)

 

To be honest, I've never seen one where Formatted is different to Raw. Then again, my program always shows Raw where possible and falls back to Formatted when it's not available (as is the case with DVD/HD DVD/Blu-ray) - so I wouldn't have ever noticed it anyway.

 

Oh and yes, you'd expect Formatted to be an interpretation (slightly cleaner looking version) of Raw data but I guess that's not always the case!

 

Perhaps the 'Formatted' info uses something from the 'Track Information' to make up it's numbers... I really have no idea!

 

I looked at the different modes in CDTool and indeed the "formatted" and "raw" view in the mode entitled "full TOC info" returns the same information consistent with your "TOC info" (i.e. Track 8 start at 38:35:00 or sector 173475). The mode entitled "all complete sessions TOC info" (which I mistook for the formatted version of raw TOC data) is consistent with your "track info" (i.e. Track 8 start at 38:35:15 or sector 173490). I used CDTool to check subchannel Q data for sector 173475 and 173490, and the latter appears to be the correct start of Track 8, as the pre-track gap count-down is at 0, whereas for 173475 it is at 15.

 

The only people that could answer that question are the ones programming the firmware in the drive.

I would have assumed all this stuff came directly from the drive so moving it between computers shouldn't have made any difference. It's very weird if you're saying it did - perhaps some filter driver is messing things up?

 

Unfortunately, I think the firmware is off the hook for now, considering the differences in behaviour of the drive in two different systems. I kind of feared this would happen, as things just got a bit more complicated. I will post any new developments...

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