Updated: 14 September 2005
normalize - adjusts volume levels of audio files.
normalize [ options ] [ -- ] file ...
normalize is used to adjust the volume of wav audio
files to a standard volume level. This is useful for things like
creating mp3 mixes, where different recording levels on different
albums can cause the volume to vary greatly from song to song.
normalize operates in two phases. In the first phase, it
analyzes the specified files as wav audio files, and computes the
volume of each file. In the second phase, it applies a volume
adjustment to each file to set each file's volume to a standard level.
- -a, --amplitude=AMPLITUDE
Adjust the RMS volume to the target amplitude AMPLITUDE; must be
between 0.0 and 1.0. If a number suffixed by "dB" or "dBFS" is
specified, the amplitude is assumed to be in decibels from full scale.
The default is -12dBFS.
- -b, --batch
Enable batch mode: see BATCH MODE, below.
- -c, --compression
Deprecated. In previous versions, this enabled
the limiter, but now the limiter is enabled by default.
Disable the limiter, and just clip any samples that are too large.
Same effect as -l 0dBFS.
Display all values as decimal fractions instead of in decibels. By
default, volume adjustments are shown in decibels, and volume levels
in dBFS, where 0 dBFS is the level of a square wave of maximum
- -g, --gain=GAIN
Skip the volume computation phase: don't compute the volume adjustment
from the current volumes of the files. Instead, just apply the given
gain as a volume adjustment to all files. As a plain number this is
just a multiplier applied to all samples, If a number suffixed by "dB"
is specified, all volumes are adjusted by that many decibels.
Use this option when adjusting MPEG audio files if your MP3 player
does not recognize ID3v2.4 tags. See MPEG
AUDIO ADJUSTMENT, below, for details.
Use this option when adjusting MPEG audio files if your MP3 player
does not recognize ID3v2 tags and has trouble playing some ID3v2
tagged MP3 files. See MPEG AUDIO
ADJUSTMENT, below, for details.
- -l, --limiter=LEVEL
This controls the behavior of the limiter. By default, all samples
above -6dBFS (0.5) are limited, but this option sets the limiting
level to LEVEL. Setting
LEVEL to 1 (or 0dBFS) does no limiting
(clipping is done instead); setting LEVEL
to 0 does limiting on all samples. The default value is recommended
unless you know what you're doing.
- -m, --mix
Enable mix mode: see MIX MODE, below.
Batch mode and mix mode are mutually exclusive.
- -n, --no-adjust
Compute and output the volume adjustment that would set the volume to
the target, but don't apply it to any of the files (i.e. skip the
second phase). If you use this option, your files will not be altered
in any way.
Don't print any progress information. All other messages are printed
as normal according to the verbosity level.
Adjust using peak levels instead of RMS levels. Each file will be
adjusted so that its maximum sample is at full scale. This just gives
a file the maximum volume possible without clipping; no normalization
- -q, --quiet
Don't output progress information. Only error messages are printed.
- -t, --average-threshold=THRESHOLD
When averaging volume levels for batch mode or mix mode, throw out any
volumes that are more than THRESHOLD
decibels from the average. A high value here (say, 50) will make sure
that the volumes of all files are considered in the average.
- -T, --adjust-threshold=THRESHOLD
If an adjustment to be made to a file is smaller than
THRESHOLD decibels, consider the file
already normalized and don't do the adjustment. This is 0.125 by
default, or 0 if the -g option is given.
- -v, --verbose
Increase verbosity. This option can be repeated for more messages.
- -w, --output-bitwidth
Force output files to have samples that are W bits wide. This option
is ignored when adjusting MP3 files.
- -h, --help
Display usage information and exit.
- -V, --version
Print version information and exit.
Terminate option list.
This mode is made especially for making mixed CD's and the like. You
want every song on the mix to be the same volume, but it doesn't
matter if they are the same volume as the songs on some other mix you
made last week. In mix mode, average level of all the files is
computed, and each file is separately normalized to this average
When operating on a group of unrelated files, you usually want all of
them at the same level, and this is the default behavior. However, a
group of music files all from the same album is generally meant to be
listened to at the relative volumes they were recorded at. In batch
mode, all the specified files are considered to be part of a single
album and their relative volumes are preserved. This is done by
averaging the volumes of all the files, computing a single adjustment
from that, and applying the same adjustment to all the files. Some
analysis is also done so that files with volumes that appear to be
statistical aberrations are not considered in the average. This is
useful if you have albums (like many of the author's) in which there
is one "quiet song" that throws off the average.
MPEG AUDIO ADJUSTMENT
MP3 files are "adjusted" by setting a relative volume
adjustment frame in their ID3 tags. There is a frame for
this, called "RVA2", that does exactly what we want, and is a native
frame in ID3v2.4. Unfortunately, many MP3 players do not support v2.4
tags, and the RVA2 tag is not native in previous ID3 versions. In
fact, adding an RVA2 frame to a v2.3 tag confuses some MP3 players.
Therefore, we are left with two choices when trying to add volume
adjustment information to an ID3 tag:
Go ahead and upgrade the tag to version 2.4, and use RVA2 tags. This
is the default behavior, in the hope that eventually MP3 players will
support v2.4 tags and this won't be a problem anymore.
Upgrade the tag to only version 2.3. Instead of RVA2, use an "XRVA"
tag with the same format as an RVA2 tag. This isn't a native frame,
but since it starts with an "X", it's considered experimental and
therefore legal, according to the ID3 spec. The
--id3-compat option turns on this behavior.
The disadvantage of the first method is that your MP3 player may no
longer read the ID3 tags on your files. Bug the author of your
favorite MP3 player to support ID3v2.4 tags!
The disadvantage of the second method is that the XRVA frame is only
recognized by the xmms-rva plugin that is packaged with normalize. On
the other hand, I don't know of any MP3 players that recognize the
RVA2 frame, either, so it may not make any difference.
The other option related to ID3 tags,
--id3-unsync, is only necessary for
compatibility with old MP3 players that don't recognize ID3v2 tags at
all. If your MP3 player complains of garbage at the start of tagged
files, or is unable to play the files at all, turn this option on.
This option should never hurt, but if your MP3 player knows about
ID3v2 tags, you don't need it.
Note that your version of normalize must be
compiled with MAD library support to analyze MP3 file volume levels.
Chris Vaill <firstname.lastname@example.org>