Provided by: sox_14.0.0-5_i386
SoX - Sound eXchange, the Swiss Army knife of audio manipulation
sox [global-options] [format-options] infile1
[[format-options] infile2] ... [format-options] outfile
[effect [effect-options]] ...
play [global-options] [format-options] infile1
[[format-options] infile2] ... [format-options]
[effect [effect-options]] ...
rec [global-options] [format-options] outfile
[effect [effect-options]] ...
SoX reads and writes audio files in most popular formats and can
optionally apply effects to them; it can combine multiple input
sources, synthesise audio, and, on many systems, act as a general
purpose audio player or a multi-track audio recorder.
The entire SoX functionality is available using just the ‘sox’ command,
however, to simplify playing and recording audio, if SoX is invoked as
‘play’, the output file is automatically set to be the default sound
device and if invoked as ‘rec’, the default sound device is used as an
The heart of SoX is a library called libSoX. Those interested in
extending SoX or using it in other programs should refer to the libSoX
manual page: libsox(3).
The overall SoX processing chain can be summarised as follows:
Input(s) → Balancing → Combiner → Effects → Output
To show how this works in practise, here are some examples of how SoX
might be used. The simple:
sox recital.au recital.wav
translates an audio file in Sun AU format to a Microsoft WAV file,
sox recital.au -r 12000 -1 -c 1 recital.wav vol 0.7 dither
performs the same format translation, but also changes the audio
sampling rate & sample size, down-mixes to mono, and applies the vol
and dither effects.
sox -r 8000 -u -1 -c 1 voice-memo.raw voice-memo.wav
adds a header to a raw audio file,
sox slow.aiff fixed.aiff speed 1.027 rabbit -c0
adjusts audio speed using the most accurate rabbit algorithm,
sox short.au long.au longer.au
concatenates two audio files, and
sox -m music.mp3 voice.wav mixed.flac
mixes together two audio files.
play "The Moonbeams/Greatest/*.ogg" bass +3
plays a collection of audio files whilst applying a bass boosting
play -n -c1 synth sin %-12 sin %-9 sin %-5 sin %-2 fade q 0.1 1 0.1
plays a synthesised ‘A minor seventh’ chord with a pipe-organ sound,
rec -c 2 test.aiff trim 0 10
records 10 seconds of stereo audio, and
rec -M take1.aiff take1-dub.aiff
records a new track in a multi-track recording.
Further examples are included throughout this manual; more-detailed
examples can be found in soxexam(7).
There are two types of audio file format that SoX can work with. The
first is ‘self-describing’; these formats include a header that
completely describes the characteristics of the audio data that
follows. The second type is ‘headerless’ (or ‘raw data’); here, the
audio data characteristics must be described using the SoX command
The following four characteristics are sufficient to describe the
format of audio data such that it can be processed with SoX:
The sample rate in samples per second (‘Hertz’ or ‘Hz’). For
example, digital telephony traditionally uses a sample rate of
8000 Hz (8 kHz); audio Compact Discs use 44100 Hz (44.1 kHz).
The number of bits used to store each sample. Most popular are
8-bit (one byte) and 16-bit (two bytes). (Since many now-common
sound formats were invented when most computers used a 16-bit
word, two bytes is often called a ‘word’, but since current
personal computers overwhelmingly have 32-bit or 64-bit words,
this usage is confusing, and is not used in the SoX
The way in which each audio sample is represented (or
‘encoded’). Some encodings have variants with different byte-
orderings or bit-orderings; some ‘compress’ the audio data, i.e.
the stored audio data takes up less space (i.e. disk-space or
transmission band-width) than the other format parameters and
the number of samples would imply. Commonly-used encoding types
include floating-point, μ-law, ADPCM, signed linear, and FLAC.
The number of audio channels contained in the file. One
(‘mono’) and two (‘stereo’) are widely used.
The term ‘bit-rate’ is sometimes used as an overall measure of an audio
format and may incorporate elements of all of the above.
Most self-describing formats also allow textual ‘comments’ to be
embedded in the file that can be used to describe the audio in some
way, e.g. for music, the title, the author, etc.
One important use of audio file comments is to convey ‘Replay Gain’
information. SoX supports applying Replay Gain information, but not
generating it. Note that by default, SoX copies input file comments to
output files that support comments, so output files may contain Replay
Gain information if some was present in the input file. In this case,
if anything other than a simple format conversion was performed then
the output file Replay Gain information is likely to be incorrect and
so should be recalculated using a tool that supports this (not SoX).
Determining & Setting The File Format
There are several mechanisms available for SoX to use to determine or
set the format characteristics of an audio file. Depending on the
circumstances, individual characteristics may be determined or set
using different mechanisms.
To determine the format of an input file, SoX will use, in order of
precedence and as given or available:
1. Command-line format options.
2. The contents of the file header.
3. The filename extension.
To set the output file format, SoX will use, in order of precedence and
as given or available:
1. Command-line format options.
2. The filename extension.
3. The input file format characteristics, or the closest to
them that is supported by the output file type.
For all files, SoX will exit with an error if the file type cannot be
determined; command-line format options may need to be added or changed
to resolve the problem.
Many file formats that compress audio discard some of the audio signal
information whilst doing so; converting to such a format then
converting back again will not produce an exact copy of the original
audio. This is the case for many formats used in telephony (e.g. A-
law, GSM) where low signal bandwidth is more important than high audio
fidelity, and for many formats used in portable music players (e.g.
MP3, Vorbis) where adequate fidelity can be retained even with the
large compression ratios that are needed to make portable players
Formats that discard audio signal information are called ‘lossy’, and
formats that do not, ‘lossless’. The term ‘quality’ is used as a
measure of how closely the original audio signal can be reproduced when
using a lossy format.
Audio file conversion with SoX is lossless when it can be, i.e. when
not using lossy compression, when not reducing the sampling rate or
number of channels, and when the number of bits used in the destination
format is not less than in the source format. E.g. converting from an
8-bit PCM format to a 16-bit PCM format is lossless but converting from
an 8-bit PCM format to (8-bit) A-law isn’t.
N.B. SoX converts all audio files to an internal uncompressed format
before performing any audio processing; this means that manipulating a
file that is stored in a lossy format can cause further losses in audio
fidelity. E.g. with
sox long.mp3 short.mp3 trim 10
SoX first decompresses the input MP3 file, then applies the trim
effect, and finally creates the output MP3 file by recompressing the
audio - with a possible reduction in fidelity above that which occurred
when the input file was created. Hence, if what is ultimately desired
is lossily compressed audio, it is highly recommended to perform all
audio processing using lossless file formats and then convert to the
lossy format at the final stage.
N.B. Applying multiple effects with a single SoX invocation will, in
general, produce more accurate results than those produced using
multiple SoX invocations; hence this is also recommended.
Clipping is distortion that occurs when an audio signal level (or
‘volume’) exceeds the range of the chosen representation. It is nearly
always undesirable and so should usually be corrected by adjusting the
volume prior to the point at which clipping occurs.
In SoX, clipping could occur, as you might expect, when using the vol
effect to increase the audio volume, but could also occur with many
other effects, when converting one format to another, and even when
simply playing the audio.
Playing an audio file often involves re-sampling, and processing by
analogue components that can introduce a small DC offset and/or
amplification, all of which can produce distortion if the audio signal
level was initially too close to the clipping point.
For these reasons, it is usual to make sure that an audio file’s signal
level does not exceed around 70% of the maximum (linear) range
available, as this will avoid the majority of clipping problems. SoX’s
stat effect can assist in determining the signal level in an audio
file; the vol effect can be used to prevent clipping, e.g.
sox dull.au bright.au vol -6 dB treble +6
guarantees that the treble boost will not clip.
If clipping occurs at any point during processing, then SoX will
display a warning message to that effect.
Input File Combining
SoX’s input combiner can combine multiple files using one of four
different methods: ‘concatenate’, ‘sequence’, ‘mix’, or ‘merge’. The
default method is ‘sequence’ for play, and ‘concatenate’ for rec and
For all methods other than ‘sequence’, multiple input files must have
the same sampling rate; if necessary, separate SoX invocations can be
used to make sampling rate adjustments prior to combining.
If the ‘concatenate’ combining method is selected (usually, this will
be by default) then the input files must also have the same number of
channels. The audio from each input will be concatenated in the order
given to form the output file.
The ‘sequence’ combining method is selected automatically for play. It
is similar to ‘concatenate’ in that the audio from each input file is
sent serially to the output file, however here the output file may be
closed and reopened at the corresponding transition between input files
- this may be just what is needed when sending audio to an output
device, but is not generally useful when the output file is a normal
If the ‘mix’ combining method is selected (with -m) then two or more
input files must be given and will be mixed together to form the output
file. The number of channels in each input file need not be the same,
however, SoX will issue a warning if they are not and some channels in
the output file will not contain audio from every input file. A mixed
audio file cannot be un-mixed.
If the ‘merge’ combining method is selected (with -M), then two or more
input files must be given and will be merged together to form the
output file. The number of channels in each input file need not be the
same. A merged audio file comprises all of the channels from all of
the input files; un-merging is possible using multiple invocations of
SoX with the mixer effect. For example, two mono files could be merged
to form one stereo file; the first and second mono files would become
the left and right channels of the stereo file.
When combining input files, SoX applies any specified effects
(including, for example, the vol volume adjustment effect) after the
audio has been combined; however, it is often useful to be able to set
the volume of (i.e. ‘balance’) the inputs individually, before
combining takes place.
For all combining methods, input file volume adjustments can be made
manually using the -v option (below) which can be given for one or more
input files; if it is given for only some of the input files then the
others receive no volume adjustment. In some circumstances, automatic
volume adjustments may be applied (see below).
The -V option (below) can be used to show the input file volume
adjustments that have been selected (either manually or automatically).
There are some special considerations that need to made when mixing
Unlike the other methods, ‘mix’ combining has the potential to cause
clipping in the combiner if no balancing is performed. So here, if
manual volume adjustments are not given, to ensure that clipping does
not occur, SoX will automatically adjust the volume (amplitude) of each
input signal by a factor of ¹/n, where n is the number of input files.
If this results in audio that is too quiet or otherwise unbalanced then
the input file volumes should be set manually as described above.
If mixed audio seems loud enough at some points through the audio but
too quiet in others, then dynamic-range compression should be applied
to correct this - see the compand effect.
Usually SoX will complete its processing and exit automatically,
however if desired, it can be terminated by pressing the keyboard
interrupt key (usually Ctrl-C). This is a natural requirement in some
circumstances, e.g. when using SoX to make a recording. Note that when
using SoX to play multiple files, Ctrl-C behaves slightly differently:
pressing it once causes SoX to skip to the next file; pressing it twice
in quick succession causes SoX to exit.
Filenames can be simple file names, absolute or relative path names, or
URLs (input files only). Note that URL support requires that wget(1)
Note: Giving SoX an input or output filename that is the same as a SoX
effect-name will not work since SoX will treat it as an effect
specification. The only work-around to this is to avoid such
filenames; however, this is generally not difficult since most audio
filenames have a filename ‘extension’, whilst effect-names do not.
The following ‘special’ filenames may be used in certain circumstances
in place of a normal filename on the command line:
- SoX can be used in pipeline operations by using the special
filename ‘-’ which, if used in place of an input filename, will
cause SoX will read audio data from ‘standard input’ (stdin),
and which, if used in place of the output filename, will cause
SoX will send audio data to ‘standard output’ (stdout). Note
that when using this option, the file-type (see -t below) must
also be given.
-n This can be used in place of an input or output filename to
specify that a ‘null file’ is to be used. Note that here, ‘null
file’ refers to a SoX-specific mechanism and is not related to
any operating-system mechanism with a similar name.
Using a null file to input audio is equivalent to using a normal
audio file that contains an infinite amount of silence, and as
such is not generally useful unless used with an effect that
specifies a finite time length (such as trim or synth).
Using a null file to output audio amounts to discarding the
audio and is useful mainly with effects that produce information
about the audio instead of affecting it (such as noiseprof or
The sampling rate associated with a null file is by default
44.1 kHz, but, as with a normal file, this can be overridden if
desired using command-line format options (see below).
One other use of -n is to use it in conjunction with -V to
display information from the audio file header without having to
read any further into the file, e.g.
sox -V *.wav -n
will display header information for each ‘WAV’ file in the
-e This is an alias of -n and is retained for backwards
These options can be specified on the command line at any point before
the first effect name.
Show version number and usage information.
Show usage information on the specified effect. The name all
can be used to show usage on all effects.
Prompt before overwriting an existing file with the same name as
that given for the output file.
N.B. Unintentionally overwriting a file is easier than you
might think, for example, if you accidentally enter
sox file1 file2 effect1 effect2 ...
when what you really meant was
play file1 file2 effect1 effect2 ...
then, without this option, file2 will be overwritten. Hence,
using this option is strongly recommended; a ‘shell’ alias,
script, or batch file may be an appropriate way of permanently
Set the size in bytes of the buffers used for reading and
writing sound data (default 8192).
Select the input file combining method; -m selects ‘mix’, -M
See Input File Combining above for a description of the
different combining methods.
If not set to off (the default if --plot is not given), run in a
mode that can be used, in conjunction with the gnuplot program
or the GNU Octave program, to assist with the selection and
configuration of many of the transfer-function based effects.
For the first given effect that supports the selected plotting
program, SoX will output commands to plot the effect’s transfer
function, and then exit without actually processing any audio.
sox --plot octave input-file -n highpass 1320 > plot.m
Run in quiet mode when SoX wouldn’t otherwise do so; this is the
opposite of the -S option.
Select whether or not to apply replay-gain adjustment to input
files. The default is track for play and off otherwise.
Display input file format/header information and input file(s)
processing progress in terms of elapsed/remaining time and
percentage complete. This option is enabled by default when
using SoX to play or record audio.
Show version number and exit.
Set verbosity. SoX prints messages to the console (stderr)
according to the following verbosity levels:
0 No messages are printed at all; use the exit status to
determine if an error has occurred.
1 Only error messages are printed. These are generated if
SoX cannot complete the requested commands.
2 Warning messages are also printed. These are generated
if SoX can complete the requested commands, but not
exactly according to the requested command parameters, or
if clipping occurs.
3 Descriptions of SoX’s processing phases are also printed.
Useful for seeing exactly how SoX is mangling your audio.
4 and above
Messages to help with debugging SoX are also printed.
By default, the verbosity level is set to 2. Each occurrence of
the -V option increases the verbosity level by 1.
Alternatively, the verbosity level can be set to an absolute
number by specifying it immediately after the -V e.g. -V0 sets
it to 0.
Input File Options
These options apply only to input files and may precede only input
filenames on the command line.
-v, --volume FACTOR
Adjust volume by a factor of FACTOR. This is a linear
(amplitude) adjustment, so a number less than 1 decreases the
volume; greater than 1 increases it. If a negative number is
given, then in addition to the volume adjustment, the audio
signal will be inverted.
See also the stat effect for information on how to find the
maximum volume of an audio file; this can be used to help select
suitable values for this option.
See also Input File Balancing above.
Input & Output File Format Options
These options apply to the input or output file whose name they
immediately precede on the command line and are used mainly when
working with headerless file formats or when specifying a format for
the output file that is different to that of the input file.
-c, --channels CHANNELS
The number of audio channels in the audio file. This may be 1,
2, or 4; for mono, stereo, or quad audio. To cause the output
file to have a different number of channels than the input file,
include this option with the output file options. If the input
and output file have a different number of channels then the
mixer effect must be used. If the mixer effect is not specified
on the command line it will be invoked internally with default
Specify the comment text to store in the output file header
SoX will provide a default comment if this option (or
--comment-file) is not given; to specify that no comment should
be stored in the output file, use --comment "" .
Specify a file containing the comment text to store in the
output file header (where applicable).
-r, --rate RATE
Gives the sample rate in Hz of the file. To cause the output
file to have a different sample rate than the input file,
include this option with the output file format options.
If the input and output files have different rates then a sample
rate change effect must be run. Since SoX has multiple rate
changing effects, the user can specify which to use as an
effect. If no rate change effect is specified then a default
one will be chosen.
-t, --type file-type
Gives the type of the audio file. This is useful when the file
extension is non-standard or when the type can not be determined
by looking at the header of the file.
The -t option can also be used to override the type implied by
an input filename extension, but if overriding with a type that
has a header, SoX will exit with an appropriate error message if
such a header is not actually present.
See soxformat(7) for a list of supported file types.
-L, --endian little
-B, --endian big
-x, --endian swap
These options specify whether the byte-order of the audio data
is, respectively, ‘little endian’, ‘big endian’, or the opposite
to that of the system on which SoX is being used. Endianness
applies only to data encoded as signed or unsigned integers of
16 or more bits. It is often necessary to specify one of these
options for headerless files, and sometimes necessary for
(otherwise) self-describing files. A given endian-setting
option may be ignored for an input file whose header contains a
specific endianness identifier, or for an output file that is
actually an audio device.
N.B. Unlike normal format characteristics, the endianness
(byte, nibble, & bit ordering) of the input file is not
automatically used for the output file; so, for example, when
the following is run on a little-endian system:
sox -B audio.uw trimmed.uw trim 2
trimmed.uw will be created as little-endian;
sox -B audio.uw -B trimmed.uw trim 2
must be used to preserve big-endianness in the output file.
The -V option can be used to check the selected orderings.
Specifies that the nibble ordering (i.e. the 2 halves of a byte)
of the samples should be reversed; sometimes useful with ADPCM-
N.B. See also N.B. in section on -x above.
Specifies that the bit ordering of the samples should be
reversed; sometimes useful with a few (mostly headerless)
N.B. See also N.B. in section on -x above.
The audio data encoding is signed linear (2’s complement),
unsigned linear, μ-law (logarithmic), A-law (logarithmic),
ADPCM, IMA-ADPCM, GSM, or floating-point.
μ-law (or mu-law) and A-law are the U.S. and international
standards for logarithmic telephone audio compression. When
uncompressed μ-law has roughly the precision of 14-bit PCM audio
and A-law has roughly the precision of 13-bit PCM audio.
A-law and μ-law are sometimes encoded using reversed bit-
ordering (i.e. MSB becomes LSB). If you need this support then
you can use the -X option or the pseudo file types of ‘.la’ and
‘.lu’ to inform SoX of the encoding. See supported file types
for more information.
ADPCM is a form of audio compression that has a good compromise
between good audio quality and fast encoding/decoding time. It
is used for telephone audio compression and places were full
fidelity is not as important. When uncompressed it has roughly
the precision of 16-bit PCM audio. Popular version of ADPCM
include G.726, MS ADPCM, and IMA ADPCM. The -a flag has
different meanings in different file handlers. In .wav files it
represents MS ADPCM files, in all others it means G.726 ADPCM.
IMA ADPCM is a specific form of ADPCM compression, slightly
simpler and slightly lower fidelity than Microsoft’s flavor of
ADPCM. IMA ADPCM is also called DVI ADPCM.
GSM is currently used for the vast majority of the world’s
digital wireless telephone calls. It utilises several audio
formats with different bit-rates and associated speech quality.
SoX has support for GSM’s original 13kbps ‘Full Rate’ audio
format. It is usually CPU intensive to work with GSM audio.
The sample datum size is 1, 2, 3, 4, or 8 bytes; i.e. 8, 16, 24,
32, or 64 bits.
Output File Format Options
These options apply only to the output file and may precede only the
output filename on the command line.
-C, --compression FACTOR
The compression factor for variably compressing output file
formats. If this option is not given, then a default
compression factor will apply. The compression factor is
interpreted differently for different compressing file formats.
See the description of the file formats that use this option in
soxformat(7) for more information.
Exit status is 0 for no error, 1 if there is a problem with the
command-line parameters, or 2 if an error occurs during file
Please report any bugs found in this version of SoX to the mailing list
soxexam(7), soxformat(7), soxeffect(7), gnuplot(1), octave(1), wget(1),
The SoX web site at http://sox.sourceforge.net
Copyright 1991 Lance Norskog and Sundry Contributors. Copyright
1998-2007 by Chris Bagwell and SoX Contributors.
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2, or (at your option) any
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
Chris Bagwell (firstname.lastname@example.org). Other authors and
contributors are listed in the AUTHORS file that is distributed with
the source code.