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Old 5th December 2011, 08:46 PM   #1
Pano is offline Pano  United States
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Question Bit Perfect MP3s?

Can an MP3 file be a bit perfect copy of a wave file? At least after it's turned back into a wave file? I was surprised to find out that it can be.

Can you guess how?
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Old 5th December 2011, 09:43 PM   #2
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Maybe if the file contains just silence? Or maybe in the case of a pure sine wave?
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Old 6th December 2011, 01:09 AM   #3
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Very good guesses. Yes, both are true.

I may try to a few more tests to see where it starts to throw away data. The format is certainly handy for some test signals as they can be uploaded in small files.
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Old 6th December 2011, 01:57 AM   #4
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The fundamental concept of “bit perfect” audio condition [Ref: #1] refers to DSP of digital source of input to destination of output with simple equation “Input = Output”. If you agree with it, then compare Wave format [Ref:#2] and MP3 format [Ref:#3]
1) Wave => DSP => MP3 (No, not Bit perfect audio condition including copying)
2) MP3 => DSP => MP3 (Yes, it can be Bit perfect audio condition if bit rate, sampling frequency, etc.. unchanged like Apple's iPod)
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Old 6th December 2011, 02:08 AM   #5
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It's not that complicated.

With a simple signal, you can encode to MP3, then decode back to an uncompressed format. There will no no difference (not one bit) between the original file and the file derived from the MP3. In that case there is NO change or loss when the file is converted back to its original format.
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Old 6th December 2011, 02:10 AM   #6
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If you disagree, not me, but the definition quoted. Then, I have nothing to say anymore.
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Old 6th December 2011, 02:14 AM   #7
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The definition doesn't worry me, the facts do.
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Old 6th December 2011, 02:29 AM   #8
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Bye Bye!
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