Not sure if I'm posting this in the right section.

I'm trying to extract 100% of the subchannel data off an audio cd. I'm using alcohol to extract the subchannel information. However, I want to make sure the subchannel data was correctly extracted. I have a program that can compare binary files bit by bit. As a test, using alcohol, I extracted RAW DAO and subchannel data multiple times. I compared the extracted images but each time the subchannel data varies somewhat. I tried extracting at various speeds such as 1X but it didn't fix the problem. How can you extract the subchannel data accurately if possible? That must be some consistency here. I'm using a plextor DVDR PX-716A. Is there another program that does a better job?

Uhm, is there any reason to extract subchannels from audio CDs? I'm using Alcohol for game CDs and the results seem very accurate (or else the copy wouldn't function). But for audio?

Well, game cds have better error correction than audio cds. Most of the protection on game cds is located in the subchannel data I believe. Alcohol has profiles to automatically extract subchannel data of course. Now, the subchannel data in audio cds is primarily used to indentify the positions of the tracks and the gaps. Although it isn't 100% perfect. Not like data or game cds are, I believe. When you backup an audio cd and burn it, the burning program should recreate the subchannel data. But that isn't perfect either. I have found it is better to extract the subchannel data from an audio cd, fix the errors and then burn to a cd-r without correcting the subchannel data. I'm trying to match the subchannel data as close as possible to the original audio cd but also being aware of read errors and fixing them. Normal audio cds don't use the R-W subchannel portion. The particular audio cd I'm copying fills the R-W portion with "FF" values instead of the standard "00" values. They are basically fillers. However, there is very little error correction in the subchannel data for audio cds, I've discovered. Therefore, the R-W portion has errors in it like "FB" where it should be "FF" In the long run this doesn't really matter for basic audio cds but if you really want a near 100% copy with subchannel data then you should get this corrected. I've written a couple of scripts in a program called Winhex to search and repair R-W errors such as "FB" and replace them with "FF" Now the P and Q subchannels are more important. I'm using other software to repair those. Once I finish all this subchannel analysis I'm then going to work with read offsets and write offsets. I've discovered a hex editor can pretty much fix anything if you know what you are doing in regards to binary data. It is great for analysis too. Audio cds are much more difficult to copy than game cds if you want to be truly accurate.