Verifying Audio CDs (Full Version)

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Dwarf -> Verifying Audio CDs (11/25/2003 7:03:57 PM)

Hey All,
I've been wondering this for a while. Is there a way to compare and verify a burn of an audio CD? I have a test CD that I've made of various test tones, sweeps and noise and it's a real pain in the butt to listen to every copy for errors. I notice that most, if not all, software will let you verify data CDs but I haven't seen that option for audio yet. I have Nero 5.5 and EZCD 6 available to me. Should I be looking at other software, or am I missing something really obvious in the software that I have?

TIA
--
Rob



sp -> RE: Verifying Audio CDs (11/26/2003 10:42:31 AM)

You need EAC. There is a whole theory behind the audio verification proccess. A good source can be found on the EAC website.

Since I was the principal person responsible for finding out, documenting and resolving all this, I will try to get you a brief description bellow.

When recording audio, at the beginning of each new session there are a few bytes of zeros being written or omitted. This is due to a different iterpretation of the standards (red-book).
So, when ripping the files back to hard disk you get the same WAV files, whith each one of them shifted to the right (or possibly left). This prohibits a person from being able to verify the identity of a file (.WAV) with respect to the copy by using the dos/command-prompt utility: "fc /b file1.wav file2.wav".

There are several ways to overcome all this.

From a practical point of view, it is acceptible to just verify the ripping of a song and ignore the offset shifting altogether. Unless you will be making copies from the copies several hundred times, there is a very littly opportunity to be any audible difference among the copy and original.

So the easiset method is: always do a testing of each riped song and compare CRC's, by using EAC. You thus eliminate the major source of problem during audio copying, which is incorect streaming of the binary data (2353 bytes/sector).
For additional verification you can do the same on the recorded disc. Transfer WAV's to hard disk and do a test CRC. This will verify that the disc is readble ok.

The CRC comparison is the safest way to go. You can also use EAC's enhanced mode ripping capabilities, but as I have found these are only 99% accurate.



ant_ -> RE: Verifying Audio CDs (11/26/2003 11:39:01 AM)


As SP correctly notes, you can also use the EAC secure mode. The program will read every audio sector at least twice. By using this technique non-identical sectors are detected. If an error occurs (read or sync error), the program keeps on reading this sector, until eight of 16 retries are identical. So, in the worst case, bad sectors are read up to 82 times. But this will help the program to obtain best result by comparing all the read retries.

On drives found to have the "accurate stream" feature, this is guaranteed. Of course, this is a little bit more complex, especially with some CD drives which have caching. When these drives cache audio data, every sector read will be read from cache and is identical. The solution in such cases is to reset the cache, by reseting the drive completely. Of course, this will slow down audio extraction.


If you don't like this feature of EAC and prefer fast copies instead of secure copies, you should use the fast or burst extraction mode in the options menu. In burst mode, it is recommended to use the "test and copy" option. For each read and each track, the appropriate CRC column is filled with the actual CRC code. One CRC code is unique for a set of data. So by comparing the CRC values you could be quite sure that both reads resulted in the same file.



Dwarf -> RE: Verifying Audio CDs (11/27/2003 4:54:54 AM)

Thank you gentlemen. I have EAC but never thought to use it to verify (getting old I guess). Since the test tone CDs have 61 tracks this sounds like the perfect way to do it. Listening to 10 minutes of pink noise for errors is really not a pleasant task :)

I'll try this out tomorrow.

--
Rob



sp -> RE: Verifying Audio CDs (11/27/2003 10:59:54 AM)

Identical CRC's is the only way to be sure about correct ripping.



Dwarf -> RE: Verifying Audio CDs (11/29/2003 8:37:23 PM)

quote:
Originally posted by sp


So the easiset method is: always do a testing of each riped song and compare CRC's, by using EAC. You thus eliminate the major source of problem during audio copying, which is incorect streaming of the binary data (2353 bytes/sector).
For additional verification you can do the same on the recorded disc. Transfer WAV's to hard disk and do a test CRC. This will verify that the disc is readble ok.


So, since I'm starting out with wav files and then burning them to CD, I'll have to burn them and then rip them back to my hard drive to compare them?

--
Rob



sp -> RE: Verifying Audio CDs (11/29/2003 10:02:21 PM)

Yes

It all depends on where the WAV's came from.
If ripping then this is the critical process.
Please do as suggested above.

If you create the WAV's from MP3, or otherwise, then do not care about the burning process too much.
Just do a C1/C2 test on the discs instead, This will let you know more about the quality of burning. Of course, you can rip again and compare, but this is a more tedious task.



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