Offset's and Confidence

[Derekpaul]

Hi There,

I am new to dBpoweramp and would like some help. I have just received the following message and would like to understand exactly what it means.

Information ripping to FLAC, 'Track 1' to 'D:\CD Music\Various Artists\Big Band 'Swing' Hits, Disc 1\01 Vic Schoen - Boogie Woogie Bugle Boy [Andrews Sisters].flac'
AccurateRip Verified Using Pressing Offset -3, Confidence 1 [new crc d0993d43]

(I actually got this message for every track on the CD)

1. I believe the offset suggests a difference between my CD drive and the one used to check to Rip. What should I be concerned about with Offsets.

2. Is a high or low confidence number good or bad?

[schmidj]

Re: Offset's and Confidence

The pressing offset is a manufacturing thing. When a CD sells a lot of copies or is re-released, a new master is made to "press" the CDs. There are likely to be minor differences in exactly where the audio starts for each track from the first masters. (as you may have discovered, on CDs, the audio doesn't start exactly at the "zero" time on the CD, for several reasons involving both the manufacturing and the way consumer players work.) Anyway, because of this there are likely to be copies of the "same" CD for some releases with many copies sold or which have been released and available for a long time with different offsets. So this copy of the CD has the third pressing offset reported to accuraterip.

The confidence is how many others have successfully ripped the same CD with the same pressing offset. The higher the better, but even for a confidence of 1, unless you ripped the very same CD before, the chances of you having a bad rip are very, very low. I don't remember the exact math with the checksums used here, but I seem to recall that the chances of a bad rip giving the same checksum on a particular track are well less than one in a million. The one case where a confidence of one might not catch a bad rip is if no one else ripped this CD with this pressing offset and you previously ripped the very same damaged copy of the CD and it somehow passed the secure rip (unlikely but possible), it got submitted to Accuraterip, and now you ripped it again and got, bit accurately, the same error again. Very unlikely.

In ripping something like 5000 CD's I have had this happen exactly once that I know of (I know I ripped the same copy of the CD twice, several years apart) The fact that the CD plays with exactly the same errors every time makes me suspect that in fact it has a manufacturing error, burnt into the CD. That does happen from time to time.

So as long as you see "accurate rip verified" on each ripped track, you should be happy, the chances that you have a bad rip are infinitesimally small.

You should have your configuration set for a secure rip (read the guidelines for details) If the CD isn't in the Accuraterip database, dBpoweramp should rip the CD tracks several times, according to how you configured it. If all the rips come up with the same checksum, the rip is considered "secure" and (on Windows) will be submitted to the database eventually to help the next person, I've seen very few "secure" rips that turned out to be bad rips.

If you have dBpoweramp configured to allow a reasonable number of "rerips" it will try to keep reripping the bad part of the track to see if it can get a consistent rip several times in a row (again, depending on how you configured the secure ripping options). I've found that all rips with rerips that weren't in Accuraterip are suspect. Listen to the ripped track. In many cases it will sound fine, a track can be far from a bit perfect copy of the CD and you'll never hear the error(s). In some cases it will have audible issues, and just like a damaged LP, you have to decide if the impairment is bad enough that you want to delete the track.

When I find a bad CD, one possibility is to go to EBay (or the library) and try to get another copy to rip. Look at the bad copy and see if cleaning it lets it rip OK. If you can acquire several different make CD (or DVD or Bluray) drives, you'll find that fairly often the CD that won't rip successfully in one make drive will rip without error in a different make drive. I have several different make "internal" drives connected with sata to USB adapters to my ripping computer and have seen over and over again that the bad (sometimes visibly damaged) CD that fails in one drive rips clean in another. (BTW, I've found that any "half height external" drives that I ever tried were very bad, compared to any internal style drive.)

Anyway, properly configured, this software is very accurate and unrecognized bad rips are few and far between.

[Derekpaul]

Re: Offset's and Confidence

Thank you Schmidj

Super helpful