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Topic: Creating image of audio disk to get exact copy (Read 4479 times) previous topic - next topic
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Creating image of audio disk to get exact copy

If I make image of an audio disk (using PowerISO) and then use Bonk Encoder to rip mp3 from the image; then wouldn't it be same as EAC+lame? --As disk image is exact and Bonk Encoder rips using lame?

Creating image of audio disk to get exact copy

Reply #1 –
Quote from: chiragv on
As disk image is exact

How do you know this for a fact?  Is PowerISO a secure CDDA ripper that provides offset correction?  Doubtful.

Creating image of audio disk to get exact copy

Reply #2 –
Don't you think that if images could be relied upon to be exact, there would be no need for programs such as Exact Audio Copy?

Put simply: On CDs, audio tracks are accompanied by less error correction information than data tracks. Therefore, to guarantee their accurate extraction, methods such as re-reading, CRCs, AccurateRip, etc. are required. Image ripping programs tend not to use these, instead simply reading the data once and dumping it. Hence EAC et al. exist.

Creating image of audio disk to get exact copy

Reply #3 –
Quote from: dv1989 on
to guarantee their accurate extraction

Unfortunately this is still all but a guarantee.  That said, your answer was probably a lot more useful than mine.

Creating image of audio disk to get exact copy

Reply #4 –
Heh, I did wonder if I should spend more time thinking of a better word, or at least put single quotes around guarantee.

Creating image of audio disk to get exact copy

Reply #5 –
Besides some exceptions mainly dealing with the exploitation of bugs in ripping software and drive firmware and/or discs with consistent manufacturing defects (some forms of copy protection can be classified as an intentional manufacturing defect), AccurateRip is pretty close to a guarantee.

Creating image of audio disk to get exact copy

Reply #6 –
If there are some text files on the compact disk and I make image of the disk, then I think the data inside the text files wouldn't be affected. Similarly it should apply for any type of file on disk. Do image making programmes run error correction for documents and not for audio files? --I don't think they make such type of distinction?

Creating image of audio disk to get exact copy

Reply #8 –
Please explain. When an image creation program creates image of data disk then the image is exact ( as data is untempered ), but the same image creation program is not able to exactly copy an audio disk. How is this possible? How can image creation program make such a distinction? It will read both the disks in same way - by seeing that which parts are burned and which are left unburned. Please explain.

Creating image of audio disk to get exact copy

Reply #9 –
The format of data CDs and audio CDs differ. When an audio CD is read by most, if not all, disc imaging apps errors are ignored / unreported and app just carries on with no attempt to correct the error.
daefeatures.co.uk

Creating image of audio disk to get exact copy

Reply #10 –
If I may borrow this thread, I have always wondered how CloneCD dealt with audio CDs, as it states that it reads all the discs bit-by-bit, which kinda sounds like a 100% guarantee that the resulting image is accurate.

However, I do understand how audio CDs differ from other type of CDs in 'file system' and I think that CloneCD (and the like) maybe does read the data bit-by-bit, however it doesn't guarantee that there were no errors when reading from an audio CD, as there is no error correction data stored on such discs.
lame -V 0

Creating image of audio disk to get exact copy

Reply #11 –
Quote
CD audio has two major design constraints that make it difficult to obtain accurate copies in the form of a standard digital file. First, the system is designed to provide audio in real time in order to ensure continuous playback without gaps. For this reason, it does not provide a reliable stream of data from the disc to the computer.

Secondly, the designers felt that it would be preferable for major scratches in the disc to be covered up rather than resulting in total failure. Normally, an error correction system such as Reed Solomon would provide either a perfect copy of the original error-free data, or no result at all. However, CD audio's Cross-interleaved Reed-Solomon coding includes an extra facility that interpolates across uncorrectable errors. This means that the data read from an audio CD may not in fact be a faithful reproduction of the original.

Link

Quote
If a major error occurs and a sample cannot be perfectly reconstructed by the error control circuitry, it is possible to "guess" the content of the sample; that is, obtain an approximation by interpolating it off the neighbouring audio samples. While this concealment will not "fix" the error, it will make it inaudible, offering a graceful degradation of audio quality as clicks and pops are avoided.

Link

Quote
Unlike a music CD, a CD-ROM cannot rely on error concealment by interpolation, and therefore requires a higher reliability of the retrieved data. In order to achieve improved error correction and detection, a CD-ROM has a third layer of Reed-Solomon error correction.

Link


Secure ripping software employs various methods of reading and analysis to attempt to ensure that the correct audio data is copied. Software which does not use secure ripping techniques will either not correct errors, return interpolated audio data, or fail to copy. I have never heard a claim or verified report of disc imaging software that uses secure ripping techniques.

Creating image of audio disk to get exact copy

Reply #12 –
'Proof' that data CDs do contain additional error correction data:

On an 700MB CD, maximum playing time is 79.8 minutes for audio CD mode.
The bit rate of an audio CD is 1411.2 kbit/s.

79.8 minutes is 4788 seconds. 4788 times 1411.2 kbit/s gives 6756825,6 kbits of data on a full audio CD.
6756825,6 kbits = 6756,8256 Mbits, which is 805,47637939453125 Mbytes!

We can see that because a data CD contains the additional error correction data, it can only store 700Mbytes of data, instead of 805,47637939453125 Mbytes available on a 700MB CD. 105,47637939453125 Mbytes go for error correction on a full 700MB data CD - additional to those 700 Mbytes.



EDIT: fixed 1024 factor instead of 1000 for bytes.
lame -V 0
 

Creating image of audio disk to get exact copy

Reply #13 –
Now I understand. Thanks to trout and everyone else.