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Am I correct that decompressing to WAV cannot reverse loss of quality?, [TOS #6: was "mp3 to wav quality" in General Audio]
Paul77
post Apr 18 2012, 14:59
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Hi

I have just used winamp to convert some mp3 files to wav for recording to cd (as the tracks are only available on Amazon as mp3 currently).

Wav's are 7 or 8 times the size of mp3's due to the compression. When you decompress to wav can you only ever get the quality that was present in the mp3. That is when the mp3 was created from the original source some loss of quality is inevitable and decompressing to wav presumably cannot reverse that loss of quality so my wav files presumably cannot sound as good as on a purchased CD.

Can someone confirm this is about right or have I missed something?

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Kohlrabi
post Apr 18 2012, 15:10
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That's about right, though good good MP3 encoders will produce files at least sound like the original file, i.e. are transparent. If you can get access to the CD, it is advisable to use that as a source. But if, like you said, you can only get this music on amazon, that means MP3 is as good as you can get?


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JimH
post Apr 18 2012, 16:31
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QUOTE (Paul77 @ Apr 18 2012, 08:59) *
I have just used winamp to convert some mp3 files to wav for recording to cd (as the tracks are only available on Amazon as mp3 currently).

Usually the software you use to burn the audio CD will make this conversion automatically. You shouldn't have to make WAV files manually.
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greynol
post Apr 18 2012, 16:39
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If such software doesn't honor gapless decoding, or if it does but the tracks weren't properly cut to CDDA frame boundaries then I wouldn't rely on it when dealing with gapless material.


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Paul77
post Apr 18 2012, 16:51
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I was using XP CD burner software so I don't think it will convert from mp3 to wav.
Out of interest I'll try converting an mp3 to wav for a track I have on a purchased CD
to see if can tell the difference (mp3 encoding is supposed to cut out frequencies that
are not audible and be efficient in compressing the rest)!





This post has been edited by Paul77: Apr 18 2012, 16:59
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greynol
post Apr 18 2012, 17:32
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That doesn't sound like it would be a proper apples to apples double-blind comparison. To compare mp3 to lossless, you need to create the mp3 from the lossless source and use something like the ABX comparator in fobar2000 in order to prevent expectation bias.


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dhromed
post Apr 18 2012, 18:39
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QUOTE (Paul77 @ Apr 18 2012, 16:51) *
I was using XP CD burner software so I don't think it will convert from mp3 to wav.


CDBurnerXP will be just fine.
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db1989
post Apr 18 2012, 18:55
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. . . because any compressed format (whether lossy or lossless) must first be decompressed to PCM at 16 bits and 44.1 kHz before it can be written to an audio CD; thus, the burning program absolutely must do this.
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benski
post Apr 18 2012, 18:56
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Decompressing an MP3 to WAV is the exact same process as playing back an MP3. You will not get back any of the original "lost" audio data. It's gone for good.

The only benefit of using Winamp to convert to do the WAV conversion will be, as Greynol pointed out, that Winamp will properly trim the lead-in and lead-out silence added by the encoding and decoding process (so called "gapless handling"). Very few decoders do this properly, and it is unlikely that your burner software is capable of it.
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Gainless
post Apr 19 2012, 11:31
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QUOTE (benski @ Apr 18 2012, 18:56) *
Decompressing an MP3 to WAV is the exact same process as playing back an MP3. You will not get back any of the original "lost" audio data. It's gone for good.

The only benefit of using Winamp to convert to do the WAV conversion will be, as Greynol pointed out, that Winamp will properly trim the lead-in and lead-out silence added by the encoding and decoding process (so called "gapless handling"). Very few decoders do this properly, and it is unlikely that your burner software is capable of it.


But how does a decoder get along with the overdrive that is there with most mp3's when it converts to WAV?
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DonP
post Apr 19 2012, 11:45
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With the right burner software, feeding it the mp3 files directly will let it use tags to fill CD text.
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greynol
post Apr 19 2012, 15:25
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QUOTE (Gainless @ Apr 19 2012, 03:31) *
But how does a decoder get along with the overdrive that is there with most mp3's when it converts to WAV?

What you mean to say is decoded samples that clip when decompressed to fixed-point. Can you demonstrate that this is audible with just one single piece of music that you would actually want to hear on your stereo? If not then this is really a non-issue!


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Paul77
post Apr 19 2012, 16:32
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QUOTE (dhromed @ Apr 18 2012, 18:39) *
QUOTE (Paul77 @ Apr 18 2012, 16:51) *
I was using XP CD burner software so I don't think it will convert from mp3 to wav.


CDBurnerXP will be just fine.


Have tried dragging and dropping mp3 file onto cd drive and then clicking on write - it does work in that a track is recorded to disk and it plays on my cd player - so presumably its a wav file but Windows Media Player changed the title to 'Track01.cda' on the disk. I guess this can be changed in the media player.

"That doesn't sound like it would be a proper apples to apples double-blind comparison. To compare mp3 to lossless, you need to create the mp3 from the lossless source and use something like the ABX comparator in fobar2000 in order to prevent expectation bias."

I imagine the mp3 file from Amazon is created from a lossless source.

Have compared an Amazon mp3 track I've on a purchased CD and its quite easy to hear the difference - just in the depth/detail of the bass and detail of the background instruments at the start of the track.

Wonder what SACD would have been like?

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db1989
post Apr 19 2012, 16:36
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Notwithstanding that being pretty obvious, the point is not about the source of Amazon’s MP3s. The point is that you didn’t compare the files in a valid way. What you have just said is in clear violation of the terms of service to which you agreed upon registering here. Perform a proper comparison and give us proper results, or stop using vague buzzwords such as “depth” and “detail” to describe what is quite probably merely a result of your expectation bias and the placebo effect.
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pdq
post Apr 19 2012, 17:02
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QUOTE (Paul77 @ Apr 19 2012, 11:32) *
Have tried dragging and dropping mp3 file onto cd drive and then clicking on write - it does work in that a track is recorded to disk and it plays on my cd player - so presumably its a wav file but Windows Media Player changed the title to 'Track01.cda' on the disk. I guess this can be changed in the media player.

'Track01.cda' is not what appears on the CD, it is only Windows' way of telling you that the CD contains no track name information.

Sometimes a CD will contain CDText information, which can be displayed by a player, but if you record the CD yourself then it requires that the burning software be capable of adding CDText, and that the track name information be supplied to it in some way.
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greynol
post Apr 19 2012, 17:52
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To add to dB1989's post, the mp3 must be compared to the actual lossless source that was used to create it. Just having the CD does not mean that the digital audio on it is the same as that used to create the mp3 that came from Amazon. It could have originated from a completely different master or be shifted in time by a noticeable amount even if it was from the same master.

QUOTE (greynol @ Apr 18 2012, 09:32) *
To compare mp3 to lossless, you need to create the mp3 from the lossless source [...]
My use of the word "the" in "the lossless source" wasn't accidental. smile.gif

Once the criteria of comparing the lossless source against its lossy counterpart is met, if the test is still not double-blind then the results are completely useless and their presentation is not welcome here.

This post has been edited by greynol: Apr 19 2012, 18:47


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Paul77
post Apr 20 2012, 13:37
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Ok so the idea is to create an mp3 from the lossless source (the cd) convert this to wav and then compare the lossless with the wav - and you need someone to play you the two recordings without you know which one is which.

Having not done an mp3 to cd comparision before my quick comparision was an interesting start
albeit not upto the rigour required here.
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soulsearchingsun
post Apr 20 2012, 13:49
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http://wiki.hydrogenaudio.org/index.php?title=ABX

edit: everything else I wrote was not adding information to this thread.

This post has been edited by soulsearchingsun: Apr 20 2012, 13:59
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db1989
post Apr 20 2012, 14:15
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QUOTE (Paul77 @ Apr 20 2012, 13:37) *
Ok so the idea is to create an mp3 from the lossless source (the cd) convert this to wav and then compare the lossless with the wav
Rip to WAV, convert WAV to MP3, compare WAV and MP3.

QUOTE
- and you need someone to play you the two recordings
Not at all: there are programs that can do this for you, e.g. foobar2000 with the official ABX comparator.

QUOTE
without you know which one is which.
This is the essential detail.

QUOTE
Having not done an mp3 to cd comparision before my quick comparision was an interesting start
albeit not upto the rigour required here.
It’ll be interesting to see what you find!

This post has been edited by db1989: Apr 20 2012, 14:20
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Gainless
post Apr 21 2012, 12:05
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QUOTE (greynol @ Apr 19 2012, 15:25) *
QUOTE (Gainless @ Apr 19 2012, 03:31) *
But how does a decoder get along with the overdrive that is there with most mp3's when it converts to WAV?

What you mean to say is decoded samples that clip when decompressed to fixed-point. Can you demonstrate that this is audible with just one single piece of music that you would actually want to hear on your stereo? If not then this is really a non-issue!


I've never heard a difference at all, but my question was more about the "no information is lost"-statement of benski. So if the overdrives in an mp3 cannot be recreated in a WAV file, is it still possible to recreate at least the "sound" of the overdrives 100%?

This post has been edited by Gainless: Apr 21 2012, 12:06
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db1989
post Apr 21 2012, 12:21
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That is nonsensical. Notwithstanding that any such clipping is already automatically transferred to a fixed-point uncompressed file if no attenuation is applied: even if it were not, why would you wish to make it so and send the decoder out of its way to do so? The goal is transparency to the original file, which, by definition, lacked the added clipping.
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lvqcl
post Apr 21 2012, 12:23
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What do you mean by "the "sound" of the overdrives" ? How they sound after clipping? How they sound if no clipping occurs?
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Gainless
post Apr 21 2012, 23:59
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I actually thought that the mp3 algorithm can make use of less information by distorting some sounds with overdrives, and just wondered if this clipping distortion can be exactly or just "approximately" recreated in a WAV file, as a gain higher than 1.00 is simply not possible, but seems to be in mp3 files. So the question is basically for me: Does a WAV contain exactly the same information as a decoded mp3 stream out of any audio player?
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splice
post Apr 22 2012, 00:30
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QUOTE (Gainless @ Apr 21 2012, 15:59) *
... So the question is basically for me: Does a WAV contain exactly the same information as a decoded mp3 stream out of any audio player?


Yes.

Think of it this way:
The decoder converts the MP3 information to standard 16 bit audio samples (assuming the original source was 16 bit stereo audio).
These samples can be:
- Fed to the DAC in your player so you can hear them.
- Written to a WAV file.
- Written to a CD.



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lvqcl
post Apr 22 2012, 00:38
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There is no clipping distortion in an MP3 file. Clipping can occur only during decoding.
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