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Audio CD Images

Discussion in 'Audio' started by Praetor, Apr 22, 2004.

  1. Praetor

    Praetor Moderator Staff Member

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    If I'm not mistaken, audio cds make use of at least 2352 bytes/sector (or more?) and since the ISO format makes use of only 2048 bytes/sector, if one tries to make an ISO image of an audio cd that happens to be copy protected, that cd-image will be worthless? Nonfunctional? Good? Would a BIN/CUE format be more effective?
     
  2. tigre

    tigre Moderator Staff Member

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    From what I've read about creating images from copyprotected audio CDs using e.g. CloneCD, the result is still copy-protected, if the source contains TOC-manipulation or similar. The audio content is extracted in burst mode by all image creation programs I know, so no error detection/correction is performed.

    On CactusDataShield protected CDs the results (= audible clicks/gaps?) mainly depends on the drive and somewhat on extraction speed, so I don't see any advantage in using ISO/BIN/CCD/... images.

    ExactAudioCopy's "Create Image and create .cue sheet" creates one big .wav file from the audio content of a CD (or a compressed one, if wanted) and a .cue file that can be used for playback or burning a copy.

    If you want a copy that additionally contains e.g. the crappy DRM'ed WMA files and playback software trying to take over your system, that are located on the data track of a CDS200 protected CD, use some image creation software like CloneCD or Alcohol120%. I've no idea if BIN/CUE or ISO is better for this. ;-)
    _X_X_X_X_X_[small]AFTERDAWN FORUM RULES: http://forums.afterdawn.com/thread_view.cfm/2487[/small]
     
    Last edited: Apr 22, 2004
  3. Praetor

    Praetor Moderator Staff Member

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    Ah thx, that cleared up some stuffos for me.... was wonderin if those extra 308 bytes/sector did anything :p

    ... damn my keyboard is sticking .... :(
     
  4. tigre

    tigre Moderator Staff Member

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    These 304 bytes/sector are used for storing audio data on audio CD (same with mode 2 data CDs) while they're used for an additional (3rd) layer of error correction on data CDs (mode 1). Audio on CD is stored as 44100 samples/second with 2 channels and 16bit = 2 byte per sample. That's 176400 Bytes/second. One second contains 75 sectors => 1 sector contains 2352 bytes of "pure" PCM audio information. No secret/hidden information in these 2352 bytes related to copy-protection or something.

    Data CDs must be read 100% error free or cause an error message by the drive (-> the whole sector is borked, ordinary windows software reports read error/corrupted file). The 304 byte/sector spent on error correction additonally helps data CDs to tolerate more damage before unrecoverable errors appear - and it gives more security against unnoticed errors.

    If a sector of an audio CD contains more errors than error correction can correct, it's not that bad. In worst case there'll be audible clicks, but due to the redundancy of PCM audio data (that's why compression works) it's enough for a drive/CD player to know the corrupt positions (and the 2 layers of error protection are enough to ensure this) . The drive can easily interpolate these positions removing audible problems caused by errors. (Of course really bad damage can make interpolation fail or even cause the drive to skip.)
     
  5. Praetor

    Praetor Moderator Staff Member

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    Ah... that clears out a lot of cobwebs and misconceptions ... thx :D
     

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