mp3gain (1) - Linux Manuals
NAME
mp3gain --- lossless mp3 normalizerSYNOPSIS
mp3gain [options] [infile] [infile 2 ...]
DESCRIPTION
This manual page documents briefly the mp3gain command.
This manual page was written for the Debian distribution
because the original program does not have a manual page.
mp3gain can analyze and adjust mp3 files
so that they have the same volume.
mp3gain does not just do peak normalization,
as many normalizers do. Instead, it does some statistical analysis to
determine how loud the file actually sounds to the human ear. Also, the
changes mp3gain makes are completely lossless. There
is no quality lost in the change because the program adjusts the mp3 file
directly, without decoding and re-encoding. Also, this works with all mp3
players, i.e. no support for a special tag or something similar is
required.
mp3gain actually changes your file's gain only
when you use one of the options -r, -a,
-g, or -l. If none of these options is
given, only a tag denoting the recommended gain change is written to the
file. If you only want to print the recommended gain change (and not modify
the file at all) you have to use the -s s (skip tag)
option.
The method mp3gain uses to determine the desired volume
is described at
www.replaygain.org (link to URL http://www.replaygain.org/) .
See also /usr/share/doc/mp3gain-1.4.6/README.method .
If you specify -r and -a,
only the second one will work.
If you do not specify -c, the program will
stop and ask before
applying gain change to a file that might clip
Here's the problem:
The "global gain" field that mp3gain adjusts is an 8-bit unsigned integer, so
the possible values are 0 to 255.
MOST mp3 files (in fact, ALL the mp3 files I've examined so far) don't go
over 230. So there's plenty of headroom on top-- you can increase the gain
by 37dB (multiplying the amplitude by 76) without a problem.
The problem is at the bottom of the range. Some encoders create frames with
0 as the global gain for silent frames.
What happens when you _lower_ the global gain by 1?
Well, in the past, mp3gain always simply wrapped the result up to 255.
That way, if you lowered the gain by any amount and then raised it by the
same amount, the mp3 would always be _exactly_ the same.
There are a few encoders out there, unfortunately, that create 0-gain frames
with other audio data in the frame.
As long as the global gain is 0, you'll never hear the data.
But if you lower the gain on such a file, the global gain is suddenly _huge_.
If you play this modified file, there might be a brief, very loud blip.
So now the default behavior of mp3gain is to _not_ wrap gain changes.
In other words,
To use the original "wrapping" behavior, use the -w switch.
This manual page was written by Stefan Fritsch sf [at] sfritsch.de for
the Debian system (but may be used by others). Permission is
granted to copy, distribute and/or modify this document under
the terms of the GNU Lesser General Public License, Version 2.1 or
any later version published by the Free Software Foundation.
The homepage of mp3gain is located at
http://mp3gain.sourceforge.net/ (link to URL http://mp3gain.sourceforge.net/) .
OPTIONS
The WRAP option
AUTHOR
SEE ALSO