File: mp3gain.1

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mp3gain 1.4.6-1
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.\" $Header: /aolnet/dev/src/CVS/sgml/docbook-to-man/cmd/docbook-to-man.sh,v 1.1.1.1 1998/11/13 21:31:59 db3l Exp $
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.TH "MP3GAIN" "1" 
.SH "NAME" 
mp3gain \(em lossless mp3 normalizer 
.SH "SYNOPSIS" 
.PP 
\fBmp3gain\fR [\fBoptions\fP]  [\fIinfile\fR]  [\fB\fIinfile 2\fR ...\fP]  
.SH "DESCRIPTION" 
.PP 
This manual page documents briefly the 
\fBmp3gain\fR       command. 
.PP 
This manual page was written for the \fBDebian\fP distribution 
because the original program does not have a manual page. 
 
.PP 
\fBmp3gain\fR analyzes and adjusts mp3 files 
so that they have the same volume. 
.PP 
\fBmp3gain\fR 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 \fBmp3gain\fR 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. 
.PP 
The method mp3gain uses to determine the desired volume 
is described at 
\fIwww.replaygain.org (link to URL http://www.replaygain.org/) \fR. 
See also \fB/usr/share/doc/README.method\fP . 
.SH "OPTIONS" 
.IP "\fB-?\fP           \fB-h\fP         " 10 
Show summary of options. 
.IP "\fB-g \fIi\fR\fP         " 10 
apply gain \fIi\fR to mp3 without 
doing any analysis 
.IP "\fB-l 0 \fIi\fR\fP         " 10 
apply gain \fIi\fR to channel 0  
(left channel) of mp3 
without doing any analysis (ONLY works for STEREO mp3s, 
not Joint Stereo mp3s) 
.IP "\fB-l 1 \fIi\fR\fP         " 10 
apply gain \fIi\fR to channel 1 
(right channel) of mp3 
without doing any analysis (ONLY works for STEREO mp3s, 
not Joint Stereo mp3s) 
.IP "\fB-r\fP         " 10 
apply Track gain automatically (all files set to equal loudness) 
.IP "\fB-k\fP         " 10 
automatically lower Track gain to not clip audio 
.IP "\fB-a\fP         " 10 
apply Album gain automatically (files are all from the same 
album: a single gain change is applied to all files, so 
their loudness relative to each other remains unchanged, 
but the average album loudness is normalized) 
.IP "\fB-m \fIi\fR\fP         " 10 
modify suggested MP3 gain by integer \fIi\fR 
.IP "\fB-d \fIn\fR\fP         " 10 
modify suggested dB gain by floating-point 
\fIn\fR 
.IP "\fB-c\fP         " 10 
ignore clipping warning when applying gain 
.IP "\fB-o\fP         " 10 
output is a database-friendly tab-delimited list 
.IP "\fB-t\fP         " 10 
mp3gain writes modified mp3 to temp file, then deletes original 
instead of modifying bytes in original file (This is the default in 
Debian) 
.IP "\fB-T\fP         " 10 
mp3gain modifys bytes in original file instead of 
writing to temp file. 
.IP "\fB-q\fP         " 10 
Quiet mode: no status messages 
.IP "\fB-p\fP         " 10 
Preserve original file timestamp 
.IP "\fB-x\fP         " 10 
Only find max. amplitude of mp3 
.IP "\fB-f\fP         " 10 
Force \fBmp3gain\fR to assume input file 
is an MPEG 2 Layer III file 
(i.e. don't check for mis-named Layer I or Layer II files) 
.IP "\fB-s c\fP         " 10 
only check stored tag info (no other processing) 
.IP "\fB-s d\fP         " 10 
delete stored tag info (no other processing) 
.IP "\fB-s s\fP         " 10 
skip (ignore) stored tag info (do not read or write tags) 
.IP "\fB-s r\fP         " 10 
force re-calculation (do not read tag info) 
.IP "\fB-u\fP         " 10 
undo changes made by mp3gain (based on stored tag info) 
.IP "\fB-w\fP         " 10 
"wrap" gain change if gain+change > 255 or gain+change < 0 
(see below or use \fB-? wrap\fP switch for a complete 
explanation) 
.IP "\fB-v\fP         " 10 
Show version of program. 
.PP 
If you specify \fB-r\fP and \fB-a\fP, 
only the second one will work. 
.PP 
If you do not specify \fB-c\fP, the program will 
stop and ask before 
applying gain change to a file that might clip 
.SS "The WRAP option" 
.PP 
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. 
 
.PP 
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. 
 
.PP 
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. 
 
.PP 
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. 
 
.PP 
So now the default behavior of mp3gain is to _not_ wrap gain changes. 
In other words, 
 
.IP "   1." 6 
If the gain change would make a frame's global gain drop below 0, 
then the global gain is set to 0. 
 
.IP "   2." 6 
If the gain change would make a frame's global gain grow above 255, 
then the global gain is set to 255. 
 
.IP "   3." 6 
 
If a frame's global gain field is already 0, it is not changed, even if 
the gain change is a positive number. 
 
.PP 
To use the original "wrapping" behavior, use the \fB-w\fP switch. 
 
.SH "SEE ALSO" 
.PP 
The homepage of mp3gain is located at 
\fIhttp://mp3gain.sourceforge.net/ (link to URL http://mp3gain.sourceforge.net/) \fR . 
 
.SH "AUTHOR" 
.PP 
This manual page was written by Stefan Fritsch sf@sfritsch.de for 
the \fBDebian\fP 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. 
 
.PP 
On Debian systems, the complete text of the GNU Lesser General Public 
License can be found in /usr/share/common-licenses/LGPL. 
 
.\" created by instant / docbook-to-man, Sun 07 Nov 2004, 22:10