Digital Audio Extraction

Digital Audio Extraction ( digital extraction of audio data DAE ) refers to the reading ( " ribs "), an audio CD with a CD -ROM drive, the audio data is not output from the analog or possibly digital audio connectors of the drive, but via the host interface ( usually ATA / ATAPI or SCSI, and the earlier Mitsumi interface) are received. The software that is used for this purpose is called a CD - Ripper, Audiograbber or simply DAE software.

Technology

, It is characteristic that

  • The host reads the data directly from the CD without these were transferred to the analog domain, as would be the case when connecting the drive via the sound card and its use;
  • The transfer is normally carried out several times faster than the complete playing of the CD;
  • The drive, as no real-time requirement is, in principle, more opportunities to process the occurrence of read errors are available.

Traditionally, the digital extraction of audio files from drive side was rather neglected, so that in particular with older drives have error correction in this case worse than when playing the CD. The signal processing in the drive takes place mostly through other circuit elements than when playing the CD. Frequently read errors are not reported to the host. Due to the fact that a data block is provided with audio with less metadata as a block of CD -ROM data, the addressability of the blocks is often limited - mainly (in rare cases, a random ) occurs dependent on the drive firmware offset, whereby the actual deviates from the read location specified by the drive to some samples.

Modern drives often have a very good error correction. Because of the opposite CD -ROM data lower redundancy of the audio material in the coding on the CD is in virtually all drives - over the rate on a data CD - the maximum read speed limited in the DAE.

To detect read errors on the one hand, the comparison with the sums of the two Prüfsummenschichten audio CDs (C1 and C2 ) are used or read the material several times and the results are compared to what is considered the safest method. ( When read errors is assumed random outcomes to the flaw. ) This reading errors can be detected largely safe, unless a read buffer of the drive is in play, otherwise only twice the result only of a real readout process is output from the buffer, which itself course is identical and so a detection of flaws in this way is impossible. Therefore, a possible read buffer must be reliably avoided for achieving reliable results. The reading errors can be detected by comparing the readout results with other users what the service AccurateRip realized by means of a database of checksums that are contributed by users.

DAE Drive Properties

The quality of the DAE is ultimately reached is defined by the properties of the specific optical disk. Properties that are useful for a perfect DAE, low offset, no jitter, a deactivatable caching and the ability to be returned the error condition (C1 and C2) correctly to the DAE software. There are databases on the properties of specific drives, also has the DAE software EAC possible to determine this automatically with a test CD.

Applications

As a reference in reliable bitperfektes reading applies to the Windows Freeware Exact Audio Copy. Widely used as a backend has found the free library cdparanoia, the DAE applications behind virtually all Linux ( and other Unix derivatives ).

Compact Disc Digital Audio CD-Ripper Host (network)
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