Re: MP3 Gain/Replay Gain

Hi Roman,

> -will Audiotron implement the gain adjustment?

No, the AudioTron currently does not do gain adjustment itself.
However, I believe that it is possible to have the AT do "real-time"
gain adjustment.  It would have to read some "gain" tag value from the
MP3 file and adjust the output volume accordingly.  Note that the AT
would only be able to adjust the volume of the analog outputs.

> -does it work well in the real world?

I think most people on this list agree that gain adjustment using
MP3Gain works pretty well.

> -can the gain adjustment be undone?

Basically: yes.  Older versions of MP3Gain generated log files that
contained the gain change applied by MP3Gain.  To undo the changes, you
had to apply the reverse change to the MP3 files one by one.  Newer
versions of MP3Gain add an APE tag containing the analysis result to the
MP3 file.  That way, the gain changes can be undo automatically.

But there's a catch.  The "undone" MP3 file is not always exactly the
same as the one you started out with.  (Even if the APE tag is removed.)
At least, this is what I think after studying the MP3Gain source code.
And I'm also not sure if this actually happens "in the real world".
Now, let me try to explain.  If eg. the MP3 file contains frames with a
"gain" value of 1, and you adjust the gain by -1, the new gain value for
those frames will be 0.  When you undo the change, MP3Gain will not
restore those frames to 1 (because of a "wrapping" protection scheme).

My point is: the MP3Gain "undo" does not always yield the original file.

> -the recent LAME 3.95.1 adds a Replay Gain value to the "LAME
   tag/header". This is distinct from the ID3 tag, and not usable by any
   hardware/software as of yet?

LAME stores the ReplayGain value in the LAME tag.  That is not the same
as an ID3v1 tag, not the same as an ID3v2 tag, and not the same as an
APE tag.

Stan
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