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For instance, an mp3 can be losslessly compressed with 7zip to about 25% of its original size. I compressed an album and the whole thing is a 1/4 of the size. Each song is about a 1/4 of the size (a good double check)

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closed as not constructive by Karan, BBlake, 8088, Nifle, Windos Nov 8 '12 at 18:54

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Sorry, I find it very hard to believe that you are getting a 25% compression on an MP3. –  Zoredache Nov 8 '12 at 8:42
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Only an mp3 encoded with a very high bitrate (ie: inefficient) can be compressed that much –  Magnetic_dud Nov 8 '12 at 8:58
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1 Answer

up vote 4 down vote accepted

The MP3 standard can encode sound to different quality levels, with different bitrates as a result. Your MP3 test sample must have been compressed to a very, very high bitrate initially. Try using a 128 kbps MP3, you'll see that it won't compress as much (if at all)

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This is a case of garbage in, garbage out. If you force the MP3 encoder to produce massive output, then it will be compressible because there was only so much information in the input. –  David Schwartz Nov 8 '12 at 9:28
    
Ah this is excellent. Very smart. Thank you you are right. –  SwimBikeRun Dec 7 '12 at 6:59
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