Join Date: May 2003
Location: Oklahoma City, Oklahoma
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The analogy gave pretty good insight as to what is happening, and I understand your description of the text file/word document idea and can see where you're having issues.
True - it is all 1's and 0's. Using your analogy, the original cd is equal to your word document. Shifting the cd to a wave file on your computer's hard drive would be like converting to a text document. You could convert these two back and forth all day and never lose anything.
MP3, AAC, etc. are all a different beast all together. The compression used by the formats is a combination of things. Reducing repetitive or similar bits into data that the codec can reassemble upon playback. So think of your word document, say that MP3 removes all of the uses of the word "the" or "an" and simply marks their location so that when you play it back they are put back into place. AAC might simply remove all of a certain letter instead, say all of the "e" and "a" 's. They are too dissimilar from one another to read the files.
Instead every conversion from MP3 to AAC is really like going from MP3 > WAV > AAC. Which would be fine, except for both MP3 and AAC are Lossy formats. They physically throw away data every time you conver to that format and it cannot be retrieved. The frequencies are supposedly "inaudible" or barely noticeable, but they are gone for good. These "compressed" areas are based on what is there, so whenever you recompress a compressed file it throws away a little more. So, in your word document, the musical frequencies you can't hear are all the words in Spanish or German you don't understand. Since you don't understand them, they are simply removed forever.....
To test what I have just said, rip an MP3 > convert it back to wav > then compress the MP3 again from that new wave. Do it like 4 times in a row, and save each progressing MP3 file. Then compare. You'll understand for sure then.
I found all this back in the original Shawn Fanning era Napster, and while I'm not proud of all the downloading I did I can tell you that I learned an invaluable lesson about audio compression. KEEP YOUR FILES, EVEN IF YOU BURN TO DISC. Now, the only MP3's I have are from my own CD collection or bought legally online.