Skip to main content ↑ ↓

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: Remove Mp3gain Tags (Read 3793 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

Remove Mp3gain Tags

How is it possible to
1) detect, if an mp3 file has been 'mp3gained'
2) undo this
?
The cli and the gui don't offer options for this (like vorbisgain does)
sic transit gloria mundi...

Remove Mp3gain Tags

Reply #1 –
It's currently not possible to detect (well, only by guessing from the displayed dB value, if it's close to 89 dB) or undo it. MP3Gain directly modifies the "global gain" value in each frame of an MP3, whereas Ogg Vorbis and MPC ReplayGain work with tags.

However, in the next MP3Gain version, the changes can be stored in an ID3v2 tag, so they can be reversed later.

Remove Mp3gain Tags

Reply #2 –
So, at the moment, its not that lossless after all, right?
If one doesn't keep the logs, the change is irreversible.
sic transit gloria mundi...

Remove Mp3gain Tags

Reply #3 –
Only lossless in the sence that it's losslessly reverseable if you know how much the files have been modified.

Remove Mp3gain Tags

Reply #4 –
Quote
Only lossless in the sence that it's losslessly reverseable if you know how much the files have been modified.

It's per definition not lossless in any sense then! You lose the original volume and cannot recreate it without additional information. 

Remove Mp3gain Tags

Reply #5 –
http://www.dictionary.com/search?q=lossless
Quote
lossless

<algorithm, compression> A term describing a data compression algorithm which retains all the information in the data, allowing it to be recovered perfectly by decompression.

No info is lost; it can be recovered perfectly.


Mp3gain help:
Quote
Lossless Gain Adjustment

The bad news: MP3Gain can only adjust the volume of your mp3 files in steps of 1.5 dB.

The good news: 1.5 dB is a small enough step for most practical purposes. Most humans can just barely hear a volume change of 1 dB.

The other good news is that this volume adjustment is completely lossless. In other words, if you adjust an mp3 by -6 dB and then change your mind, you can adjust it again by +6 dB and it will be exactly the same as it was before you made the first adjustment.

Here's the technical reason why it's lossless, and also why the smallest change possible is 1.5 dB:

The mp3 format stores the sound information in small chunks called "frames". Each frame represents a fraction of a second of sound. In each frame there is a "global gain" field. This field is an 8-bit integer (so its value can be a whole number from 0 to 255).

When an mp3 player decodes the sound in the frame, it uses the global gain field to multiply the decoded sound samples by 2(gain / 4).

So if you add 1 to this gain field in all the frames in the mp3, you effectively multiply the amplitude of the whole file by 2(1/4) = 119% = +1.5 dB.

Likewise, if you subtract 1 from the global gain, you multiply the amplitude by 2(-1/4) = 84% = -1.5 dB.

Remove Mp3gain Tags

Reply #6 –
Yes, Jan. And exactly therefor it's not lossless. It would be if the original value would be kept. At least somewhere in the file. But as the value actually CHANGES, and the change is not noted IN THE DATA, you lose information.
sic transit gloria mundi...

Remove Mp3gain Tags

Reply #7 –
Quote
Yes, Jan. And exactly therefor it's not lossless. It would be if the original value would be kept. At least somewhere in the file. But as the value actually CHANGES, and the change is not noted IN THE DATA, you lose information.

Yeah, we could play the semantics game all day

When I say MP3Gain is "lossless", I mean "no audio quality is lost while adjusting the volume." You can adjust the volume dozens or hundreds of times and never lose any quality.

But you are correct that the original volume is "lost" if you don't log it... in the current version of MP3Gain, anyhow. As mentioned above, logging the changes in ID3v2 tags is one of the first things I'll work on after the upcoming 1.0 release.

Sorry for any confusion or upset expectations.

-Glen

Remove Mp3gain Tags

Reply #8 –
Would't you loose the gain info if you remove the whole id3v2 with a tag editor (TAG etc.)?

Remove Mp3gain Tags

Reply #9 –
Quote
Would't you loose the gain info if you remove the whole id3v2 with a tag editor (TAG etc.)?

Yes, but there is no other way to store the gain value within your MP3s.

Remove Mp3gain Tags

Reply #10 –
To continue the little game, MP3Gain is 100% lossless with log files enabled.
 

Remove Mp3gain Tags

Reply #11 –
Quote
Quote
Would't you loose the gain info if you remove the whole id3v2 with a tag editor (TAG etc.)?

Yes, but there is no other way to store the gain value within your MP3s.

The LAME tag would allow it.