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mp3 to wav to mp3 to wav same?
gts
post Feb 27 2003, 14:42
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If a file is encoded to mp3, then coverted back to a wav, and then that wav is convered back to mp3, will the both mp3s be the same?
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tigre
post Sep 10 2003, 10:35
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QUOTE (Zilva @ Sep 10 2003, 01:06 AM)
Cosine transformation is NOT LOSSY. After transofmation you just cut some frequences. If you have no information in cut out freequences you get NOT LOSSY compression. So if you cut something once you can't cut it second time. There is no "rounding" or something similar. For example you have sequence of bytes '15 35 156 204 32 0 14 87 5 9 45 34 35 147 21 224' let assume that after cosine transform you have '245 125 54 2 20 6 1 2 0 1 0 0 0 0 0 0'. In order to compress you just cut off last 6 bytes. After decoding you will get exactly the same wav file. So mpeg compressin NOT ALWAYS is lossy. In case of repeatedly compresing-decompresing the same file with the same parameters you will not loose anything.
And there is no need to use 192 or even 128 kbps if your sound source is radio quality. You won't get any better qualty. Imagine that instead last 6 zeroes you will cut only 3. You just have bigger files. Here helps much VBR because it will cut more or less depending on how much zeroes you have at the end of spectrum.

Some things of what you say seem right, but leed to at least questionable conclusions. What about this?
- The transform results are stored digitally - to compress the storage space is limited, so rounding/truncation errors happen
- Unless you try to compress artificial test signals there's always noise or noise-like content (at least dither), so there are hardly any "0"s after transform
- On reencoding the positions of transform windows are different than before because mp3 encoding/decoding adds samples in the beginning
- Even if the positions would be the same, the windows overlap, so when encoding again it's not possible to restore the windows from the encoding step before exactly as they've been.

Maybe I'm wrong. Why don't you provide an example for a file that doesn't change on multiple en-/decoding? (There's an upload forum...)


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- gts   mp3 to wav to mp3 to wav same?   Feb 27 2003, 14:42
- - CiTay   No. MP3 encoding is a lossy process. The WAV that ...   Feb 27 2003, 14:46
- - gts   Well the first conversion from wav to mp3 removes ...   Feb 27 2003, 15:05
- - Xenion   QUOTE (gts @ Feb 27 2003 - 03:05 PM)Well the ...   Feb 27 2003, 15:15
- - X-Fixer   QUOTE (gts @ Feb 27 2003 - 09:05 PM)Well the ...   Feb 27 2003, 15:26
- - gts   QUOTE theoretically this could work this way. (sec...   Feb 27 2003, 23:30
- - gts   QUOTE original wav => mp3 =lossy agreed QUOTE m...   Feb 27 2003, 23:33
- - Messer   Codec does not remove anything. It rounds some val...   Feb 27 2003, 23:39
- - gts   Thank you. What search words will find the topic? ...   Feb 27 2003, 23:43
- - Mac   I'll chip in because it took me a few goes of ...   Feb 27 2003, 23:46
- - Messer   I'd try "reencoding". This is for e...   Feb 27 2003, 23:49
- - gts   Thank you!   Feb 28 2003, 00:01
- - CiTay   QUOTE Codec does not remove anything. It rounds so...   Feb 28 2003, 00:21
- - gts   QUOTE It doesn't care if the WAV was previousl...   Feb 28 2003, 00:30
- - Messer   QUOTE (CiTay @ Feb 28 2003 - 01:21 AM)QUOTE C...   Feb 28 2003, 00:35
- - gts   QUOTE that essential process in lossy compression ...   Feb 28 2003, 00:37
- - fewtch   There's a simple way to test this. Encode a ....   Feb 28 2003, 00:42
- - Artemis3   If you record a CD into a cassette tape, then use ...   Feb 28 2003, 02:14
- - gts   QUOTE If you record a CD into a cassette tape, the...   Feb 28 2003, 02:29
- - rjamorim   QUOTE (gts @ Feb 27 2003 - 08:30 PM)In the jp...   Feb 28 2003, 02:39
- - gts   QUOTE But reducing the amount of colors is only ON...   Feb 28 2003, 02:44
- - rjamorim   QUOTE (gts @ Feb 27 2003 - 10:44 PM)but the p...   Feb 28 2003, 03:05
- - andrew3199   I think we can all agree that there is some loss w...   Feb 28 2003, 04:29
- - rjamorim   QUOTE (andrew3199 @ Feb 28 2003 - 12:29 AM)fo...   Feb 28 2003, 04:36
- - dreamliner77   QUOTE I perceived the decay of plucked notes on an...   Feb 28 2003, 05:19
|- - makarov   An analogy to JPEG lossy image compression was mad...   Jan 30 2005, 07:33
- - NeoRenegade   gts, with regards to your JPEG analogy... you refe...   Mar 2 2003, 23:14
- - kdo   QUOTE (rjamorim @ Feb 28 2003 - 03:05 AM)Code...   Mar 3 2003, 00:37
- - aggies11   Not to resurrect a dead thread or anything, but it...   Aug 21 2003, 02:13
- - Doctor   aggies: no. Lossy sound encoding is not like you ...   Aug 21 2003, 02:54
- - phong   An interesting thought, but probably academic. MP...   Aug 21 2003, 02:58
- - AtaqueEG   QUOTE (dreamliner77 @ Feb 27 2003, 11:19 PM)R...   Aug 21 2003, 03:18
- - 2Bdecided   QUOTE (aggies11 @ Aug 21 2003, 01:13 AM)Could...   Aug 21 2003, 10:33
- - 2Bdecided   In reply to the original question, the simplistic ...   Aug 21 2003, 10:39
- - sld   (Redundant post, sorry)   Aug 21 2003, 10:40
- - Vietwoojagig   I remember long time ago, there was a technology c...   Aug 21 2003, 12:53
- - 2Bdecided   DCC used (what would become) MPEG-1 layer I. You ...   Aug 21 2003, 13:24
- - aggies11   Thanks for the quick replies. Very informative ind...   Aug 21 2003, 17:06
- - phong   The answer to the first question is "no...   Aug 21 2003, 19:29
- - Doctor   Yawn. phong: I think you are wrong on both counts...   Aug 22 2003, 03:29
- - phong   I think I mis-specified which questions I was answ...   Aug 22 2003, 03:46
- - Canar   QUOTE (2Bdecided @ Aug 21 2003, 01:33 AM)I do...   Aug 22 2003, 04:08
- - bexx   Isn't wavpacklossy/hybrid whatever its called ...   Aug 22 2003, 04:29
- - sublimelouie   easiest way to think of it, its like xeroxing a xe...   Aug 22 2003, 04:51
- - aggies11   Sublime: easiest way to think of it, its like xero...   Aug 22 2003, 05:26
- - 2Bdecided   This reply is in response to no one in particular....   Aug 22 2003, 11:05
- - Gabriel   QUOTE IIRC FhG looked at this. You could call it a...   Aug 22 2003, 11:23
- - smg   QUOTE (2Bdecided @ Aug 22 2003, 06:05 AM)This...   Aug 22 2003, 14:46
- - phong   QUOTE Do it enough, you can reduce the complexity ...   Aug 22 2003, 16:13
- - ErikS   QUOTE (Gabriel @ Aug 22 2003, 11:23 AM)Now, t...   Aug 22 2003, 16:50
- - Zilva   Cosine transformation is NOT LOSSY. After transofm...   Sep 10 2003, 10:06
- - tigre   QUOTE (Zilva @ Sep 10 2003, 01:06 AM)Cosine t...   Sep 10 2003, 10:35
- - 2Bdecided   QUOTE (Zilva @ Sep 10 2003, 09:06 AM)Cosine t...   Sep 10 2003, 11:11
- - MugFunky   wow.. old post. ("holy thread resurrection, b...   Jan 31 2005, 04:06
- - h.tuehn   I don't want to correct anything MugFunky or m...   Jan 31 2005, 07:16


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