CD ripper
A CD ripper (sometimes called Audiograbber called) is a software that using a CD-ROM drive audio data (mostly music ) from audio CDs read ( " rip ") and as an audio file stores. The process is also known as Digital Audio Extraction (DAE).
Many CD rippers offer the option of calling up metadata about the audio CD to be extracted from the Internet and saving it (if a suitable file format is selected ). This is how you can create music libraries on your computer.
etymology
The entry for rip in the jargon file indicates the origin of the term Amiga -Slang, where it describes the finding and isolation of media content (graphics and sounds) from programs.
history
One of the first CD rippers from the early 1990s (still under MS-DOS ) was Digital Audio Copy (DAC) by Christoph Schmelnik. The software project CDDA2Wav was started under Unix in 1993 , which is also the origin of the current cdparanoia .
Formats
The audio material on an audio CD ( CDDA ) is available as a stream of non- redundancy- reduced, pulse-code-modulated audio data. Therefore, in ripping, a natural file format is one that stores such a stream, such as. B. RIFF WAVE (".wav"). The format can be changed for use with common playback programs and to save storage space . Either a lossy codec like MP3 or Vorbis or a lossless codec like FLAC can be used for this. If a container format is selected that supports metadata (e.g. MP3, Matroska or Ogg ), further (meta) information can be provided via the audio CD (title, artist, etc.) or the DAE process (read-out date, software, etc.) .).
technology
The audio data are not output via the analog or digital audio connections of the drive, but are transmitted via the host interface (mostly Serial ATA , ATA / ATAPI or SCSI ).
It is characteristic that
- the host reads the data directly from the CD without transferring it to the analog domain, as would be the case when connecting the drive via the sound card and using it;
- the transfer is usually several times faster than playing the entire CD;
- the drive or the software, since there is no real-time requirement, there are in principle more options available for proceeding in the event of read errors.
Traditionally, the digital extraction of audio data has been neglected on the drive side, so that error correction is worse, especially with older drives, than when playing the CD. The signal processing in the drive usually takes place via different circuit components than when playing the CD. Often read errors are not reported to the host. Due to the fact that a data block with audio material is equipped with less metadata than a block with CD-ROM data, the addressability of the blocks is often restricted - usually there is an offset that is dependent on the drive firmware (in some models also random) , whereby the actual reading position deviates by a few samples from the reading position indicated by the drive.
Modern drives often have very good error correction. Because of the lower redundancy of the audio material when encoding on the CD compared to CD-ROM data , the maximum reading speed of the DAE is limited in practically all drives - compared to the speed of data CDs.
To detect read errors, on the one hand (if supported by the drive) the error correction signals ( C1 and C2 errors ) can be evaluated in the drive or the material can be read several times and the results compared, which is considered the safest method. (In the case of read errors, random results are assumed at the error locations.) This means that read errors can be largely reliably detected, provided that a read buffer of the drive is not involved, since otherwise the result of only one real read process is output from the buffer, which is itself is of course identical and so it is impossible to detect faulty areas in this way. A possible read buffer must therefore be reliably bypassed in order to achieve reliable results. Furthermore, reading errors can be detected by comparing the reading results with other users, which the AccurateRip service does by means of a database of checksums that are contributed by users.
DAE drive properties
The quality that can ultimately be achieved is - in addition to the condition of the medium, i.e. the CD - defined by the properties of the specific optical drive.
Features that are helpful for DAE are a low offset , no jitter , caching that can be deactivated and the ability to correctly report the error status (C1 and C2) back to the DAE software. There are databases on the properties of specific drives. The DAE software EAC offers the possibility of automatically determining the drive properties with a test CD.
The support of various CD ripper software for helpful and annoying drive properties is very different and should be taken into account; z. B. EAC was one of the first DAE programs to evaluate C2 error information at all.
software
Many popular operating systems come with pre-installed CD rippers. Many audio players can also rip CDs.
Common CD rippers include:
| BSD and Linux | Mac OS | Windows |
|---|---|---|
See also
Web links
- Difficulties reading audio CDs (English)
- www.daefeatures.co.uk/ , database on optical drives and their DAE properties (English)
Footnotes
- ↑ rip . In: The Jargon File (version 4.4.3) . catb.org. July 1, 2003. Archived from the original on February 24, 2009. Retrieved on March 28, 2011.
- ↑ http://www.muenster.de/~asshoff/physik/cd/cdplayer.htm
- ↑ DAE Drive Features Database - FAQ ( Memento of the original from January 16, 2006 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. ( English , 2007)
