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Understanding Rippers and Accuraterip Submissions
post Sep 10 2012, 15:48
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I'm trying to learn more about the process of ripping and how it works in regards to Accuraterip.

"For example, audio CDs contain 16-bit, 44.1 KHz LPCM-encoded audio samples interleaved with secondary data streams and synchronization and error correction info. The ripping software tells the CD drive's firmware to read this data and parse out just the LPCM samples. The software then dumps them into a WAV or AIFF file, or feeds them to another codec to produce, for example, a FLAC or MP3 file."


If I insert a CD from say Led Zepplin's box set of complete studio recordings, or an Elton John hybrid SACD, or a CD that's been remastered, how does a ripper and Accuraterip differentiate and correctly identify which of the recordings I have? If the selection the ripper returns in identifying the media is wrong (the media is a 2009 remaster and the ripper claims it is the original 1973 disc) and I don't change/correct it, how does that affect the database?
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post Sep 10 2012, 18:52
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It would be quite impressive to find a CD from 1973, considering they didn't exist until the mid-1980s, but anyway... audio CDs generally don't contain IDs or metadata. When an ID is needed, such as to look up metadata (artist/title/date/etc.) or look up pressings in the AccurateRip database, an ID is generated by the software that needs it. There are different ways of generating a disc ID, but they are basically just different ways of summarizing the info encoded in the disc's Table Of Contents (TOC), which gets read as soon the disc is inserted in a player or drive. The TOC contains a list of start positions (precision: 1/75th of a second) for each track. The number of tracks and their durations can be derived from the this. As you can imagine, there are occasional collisions, but for purposes of AccurateRip, it doesn't matter; the odds of two albums having the same TOC and the same AR checksum are pretty slim! The remastered Led Zep album has a different track layout...maybe the same number of tracks, but the boundaries are not going to match up with the original editions at all.

Regarding minor errors in our wiki article on AccurateRip, although I wrote most of it, it was Spoon(!) who added the 'Pressings' section about ARv2. And I was careful to use the word checksum, but accidentally used the term CRC when linking to Spoon's explanation of the algorithm; I fixed it just now, but it's an understandable oversight since Spoon himself characterizes the checksum as a CRC. smile.gif

As for superfluous info... not to say that using the forum's search tools isn't a good idea, but I feel the wiki is there to make it so people don't have to keep searching for and referring to half-remembered posts scattered throughout a decade-plus archive of the forums. Most people aren't very good at searching; the key in this case would be to search for AccurateRip disc identification, which would lead to the following thread: http://www.hydrogenaudio.org/forums/index....showtopic=79082 (jayess, please read that thread).

The wiki is also there to explain—hopefully simplifying, without compromising—technical subjects that aren't documented very well elsewhere. In this instance, we really needed to get redundant AR and related technical info out of the EAC docs and ripping guides, and we needed to aggregate and summarize AR-related info that was scattered throughout forum postings. We could stand to move the general drive offset info to a separate article, sure, but there are only so many hours in the day. If anything, the AR article needs to be expanded to give some examples of the database in action, interpreting verification results, and answering any other questions that people have about the subject, such as jayess's question about how discs are identified.
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Posts in this topic
- jayess   Understanding Rippers and Accuraterip Submissions   Sep 10 2012, 15:48
- - greynol   AR records are based on the lengths of tracks (inc...   Sep 10 2012, 15:54
- - pdq   There are multiple online databases of CD metadata...   Sep 10 2012, 16:04
- - greynol   That wikipedia article has nothing to do with AR e...   Sep 10 2012, 16:10
- - Tahnru   HA has a very nice wiki. http://wiki.hydrogenaud...   Sep 10 2012, 16:27
- - greynol   Not the best article I've seen but not the wor...   Sep 10 2012, 16:52
- - mjb2006   It would be quite impressive to find a CD from 197...   Sep 10 2012, 18:52
- - greynol   I don't care who added it. From the standpoint...   Sep 10 2012, 19:05
- - jayess   To put this into perspective, when I insert this d...   Sep 10 2012, 19:16
- - db1989   Wow… Just wow. The album was first released in ...   Sep 10 2012, 19:40
|- - jayess   QUOTE (db1989 @ Sep 10 2012, 13:40) Wow… ...   Sep 10 2012, 19:46
- - pdq   Many different people submit CD metadata to the da...   Sep 10 2012, 19:58
|- - jayess   QUOTE (pdq @ Sep 10 2012, 13:58) Many dif...   Sep 10 2012, 20:04
||- - greynol   QUOTE (jayess @ Sep 10 2012, 12:04) I fix...   Sep 10 2012, 20:32
||- - greynol   QUOTE (greynol)What are pressings according to AR ...   Sep 10 2012, 20:48
|- - jayess   QUOTE (pdq @ Sep 10 2012, 13:58) Many dif...   Sep 10 2012, 20:19
- - greynol   The last question was there to address an explanat...   Sep 10 2012, 20:23
- - godrick   mjb2006, I heartily agree a single reference wiki ...   Sep 10 2012, 22:29
- - jayess   This stuff does make you go h'mmm. I find out ...   Sep 11 2012, 13:49
- - pdq   When you first put the CD in, it reads the TOC and...   Sep 11 2012, 14:22

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