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.TH SoX 1 "July 1, 2008" "sox" "Sound eXchange"
.SH NAME
SoX \- Sound eXchange, the Swiss Army knife of audio manipulation
.SH SYNOPSIS
.nf
\fBsox\fR [\fIglobal-options\fR] [\fIformat-options\fR] \fIinfile1\fR
[[\fIformat-options\fR] \fIinfile2\fR] ... [\fIformat-options\fR] \fIoutfile\fR
[\fIeffect\fR [\fIeffect-options\fR]] ...
.SP
\fBplay\fR [\fIglobal-options\fR] [\fIformat-options\fR] \fIinfile1\fR
[[\fIformat-options\fR] \fIinfile2\fR] ... [\fIformat-options\fR]
[\fIeffect\fR [\fIeffect-options\fR]] ...
.SP
\fBrec\fR [\fIglobal-options\fR] [\fIformat-options\fR] \fIoutfile\fR
[\fIeffect\fR [\fIeffect-options\fR]] ...
.fi
.SH DESCRIPTION
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.
.SP
Almost all SoX functionality is available using just the \fBsox\fR command,
however, to simplify playing and recording audio, if SoX is invoked as
\fBplay\fR the output file is automatically set to be the default sound
device and if invoked as \fBrec\fR the default sound device is used as an
input source.
The
.BR soxi (1)
command provides a convenient way to just query audio file header information.
.SP
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:
.BR libsox (3).
.SP
The overall SoX processing chain can be summarised as follows:
.TS
center;
l.
Input(s) \*(RA Balancing \*(RA Combiner \*(RA Effects \*(RA Output
.TE
.DT
.SP
To show how this works in practise, here are some examples of how
SoX might be used. The simple
.EX
sox recital.au recital.wav
.EE
translates an audio file in Sun AU format to a Microsoft WAV file, whilst
.EX
sox recital.au -r 12k -1 -c 1 recital.wav vol 0.7 dither
.EE
performs the same format translation, but also changes the audio
sampling rate & sample size, down-mixes to mono, and applies
the \fBvol\fR and \fBdither\fR effects.
.EX
sox -r 8k -u -1 -c 1 voice-memo.raw voice-memo.wav
.EE
adds a header to a raw audio file,
.EX
sox slow.aiff fixed.aiff speed 1.027
.EE
adjusts audio speed,
.EX
sox short.au long.au longer.au
.EE
concatenates two audio files, and
.EX
sox -m music.mp3 voice.wav mixed.flac
.EE
mixes together two audio files.
.EX
play \(dqThe Moonbeams/Greatest/*.ogg\(dq bass +3
.EE
plays a collection of audio files whilst applying a bass boosting effect,
.EX
play -n -c1 synth sin %-12 sin %-9 sin %-5 sin %-2 fade q 0.1 1 0.1
.EE
plays a synthesised `A minor seventh' chord with a pipe-organ sound,
.EX
rec -c 2 test.aiff trim 0 10
.EE
records 10 seconds of stereo audio, and
.EX
rec -M take1.aiff take1-dub.aiff
.EE
records a new track in a multi-track recording.
.SP
Further examples are included throughout this manual;
more-detailed examples can be found in
.BR soxexam (7).
.SS File Formats
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 line.
.SP
The following four characteristics are sufficient to describe
the format of audio data such that it can be processed with SoX:
.TP
sample rate
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\*d1\ kHz).
.TP
sample size
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 documentation.)
.TP
data encoding
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, \(*m-law, ADPCM, signed linear,
and FLAC.
.TP
channels
The number of audio channels contained in the file. One (`mono') and two
(`stereo') are widely used.
.PP
The term `bit-rate' is sometimes used as an overall measure of an audio
format and may incorporate elements of all of the above.
.SP
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.
.SP
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).
.SP
The
.BR soxi (1)
command can be used to display information from audio file headers.
.SS 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.
.SP
To determine the format of an input file, SoX will use, in order of
precedence and as given or available:
.SP
.TS
tab (@);
l l l.
@1.@Command-line format options.
@2.@The contents of the file header.
@3.@The filename extension.
.TE
.DT
.SP
To set the output file format, SoX will use, in order of
precedence and as given or available:
.SP
.TS
tab (@);
l l lw(6i).
@1.@Command-line format options.
@2.@The filename extension.
@3.@T{
The input file format characteristics, or the closest
to them that is supported by the output file type.
T}
.TE
.DT
.SP
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.
.SS Play, Rec, & Default Audio Devices
Some systems provide more than one type of (SoX-compatible) audio
driver, e.g. ALSA & OSS, or SUNAU & AO.
Systems can also have more than one audio device (a.k.a. `sound card').
If more than one audio driver has been
built-in to SoX, and the default selected by SoX when using
.B rec
or
.B play
is not the one that is wanted, then the
.B AUDIODRIVER
environment variable can be used to override the default. For example
(on many systems):
.EX
set AUDIODRIVER=oss
play ...
.EE
For
.BR rec ,
.BR play ,
and
.BR sox ,
the
.B AUDIODEV
environment variable can be used to override the default audio device;
e.g.
.EX
set AUDIODEV=/dev/dsp2
play ...
sox ... -t oss
.EE
or
.EX
set AUDIODEV=hw:0
play ...
sox ... -t alsa
.EE
(Note that the syntax of the
.B set
command may vary from system to system.)
.SP
When playing a file with a sample rate that is not supported by the
audio output device, SoX will automatically invoke the \fBrate\fR effect
to perform the necessary sample rate conversion. For
compatibility with old hardware, here, the
default \fBrate\fR quality level is set to `low'; however, this
can be changed if desired, by explicitly specifing the \fBrate\fR
effect with a different quality level, e.g.
.EX
play ... rate -m
.EE
or by setting the environment varible
.B PLAY_RATE_ARG
to the desired quality option, e.g.
.EX
set PLAY_RATE_ARG=-m
play ...
.EE
(Note that the syntax of the
.B set
command may vary from system to system.)
.SP
To help with setting a suitable recording level, SoX includes a simple VU
meter which can be invoked (before making the actual recording) as follows:
.EX
rec -n
.EE
The recording level should be adjusted (using the system mixer program) so
that the meter is \fIat most occasionally\fR full scale, and never `in the
red' (an exclamation mark is shown).
.SS Accuracy
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 practical.
.SP
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.
.SP
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.
.SP
.B 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
.EX
sox long.mp3 short.mp3 trim 10
.EE
SoX first decompresses the input MP3 file, then applies the
.B trim
effect, and finally creates the output MP3 file by recompressing the
audio\*mwith 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 only at the final stage.
.SP
.B 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.
.SS Clipping
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.
.SP
In SoX, clipping could occur, as you might expect, when using the
.B 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.
.SP
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.
.SP
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
.B stat
effect can assist in determining the signal level in an audio file; the
.B gain
or
.B vol
effect can be used to prevent clipping, e.g.
.EX
sox dull.au bright.au gain -6 treble +6
.EE
guarantees that the treble boost will not clip.
.SP
If clipping occurs at any point during processing, then
SoX will display a warning message to that effect.
.SS Input File Combining
SoX's input combiner can combine multiple files using any of the
following methods: `concatenate', `sequence', `mix', or `merge'.
The default method is `sequence' for
.BR play ,
and `concatenate' for
.B rec
and
.BR sox .
.SP
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.
.SP
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.
.SP
The `sequence' combining method is selected automatically for
.BR 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\*mthis 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
file.
.SP
If the `mix' combining method is selected (with \fB-m\fR) 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 (without reference to the
orignal input files).
.SP
If the `merge' combining method is selected (with \fB-M\fR), 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
.B 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.
.SP
When combining input files, SoX applies any specified effects
(including, for example, the
.B 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.
.SP
For all combining methods, input
file volume adjustments can be made manually using the
.B \-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).
.SP
The \fB\-V\fR option (below) can be used to show the input file volume
adjustments that have been selected (either manually or automatically).
.SP
There are some special considerations that need to made when mixing
input files:
.SP
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 \(S1/\s-2n\s+2,
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.
.SP
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\*msee the
.B compand
effect.
.SS Stopping SoX
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.
.SH FILENAMES
Filenames can be simple file names, absolute or relative path names,
or URLs (input files only). Note that URL support requires that
.BR wget (1)
is available.
.SP
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.
.SP
The following `special' filenames may be used in certain circumstances
in place of a normal filename on the command line:
.TP
\fB\-\fR
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
.B \-t
below) must also be given.
.TP
\fB\-d\fR
This can be used in place of an input or output filename to specify that
the default audio device (if one has been built into SoX) is to be used.
This is akin to invoking
.B rec
or
.B play
(as described above).
.TP
\fB\-n\fR
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.
.SP
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 \fBtrim\fR or \fBsynth\fR).
.SP
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 \fBnoiseprof\fR or \fBstat\fR).
.SP
The sampling rate associated with a null file
is by default 48\ kHz, but, as with a normal
file, this can be overridden if desired using command-line format
options (see below).
.SH OPTIONS
.SS Global Options
These options can be specified on the command line at any point
before the first effect name.
.TP
\fB\-h\fR, \fB\-\-help\fR
Show version number and usage information.
.TP
\fB\-\-help\-effect=\fINAME\fR
Show usage information on the specified effect. The name
\fBall\fR can be used to show usage on all effects.
.TP
\fB\-\-help\-format=\fINAME\fR
Show information about the specified file format. The name
\fBall\fR can be used to show information on all formats.
.TP
\fB\-\-interactive\fR
Prompt before overwriting an existing file with the same name as that
given for the output file.
.SP
.B N.B.
Unintentionally overwriting a file is easier than you might think, for
example, if you accidentally enter
.EX
sox file1 file2 effect1 effect2 ...
.EE
when what you really meant was
.EX
play file1 file2 effect1 effect2 ...
.EE
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 enabling it.
.TP
\fB\-\-buffer\fR \fBBYTES\fR
Set the size in bytes of the buffers used for reading and writing sound data (default 8192).
.TP
\fB\-m\fR\^|\^\fB\-M\fR\^|\^\fB\-\-combine concatenate\fR\^|\^\fBmerge\fR\^|\^\fBmix\fR\^|\^\fBsequence\fR
Select the input file combining method;
.B \-m
selects `mix',
.B \-M
selects `merge',
.SP
See \fBInput File Combining\fR above for a description of the different
combining methods.
.TP
\fB\-\-plot gnuplot\fR\^|\^\fBoctave\fR\^|\^\fBoff\fR
If not set to
.B off
(the default if
.B \-\-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. E.g.
.EX
sox --plot octave input-file -n highpass 1320 > plot.m
octave plot.m
.EE
.TP
\fB\-q\fR, \fB\-\-no\-show\-progress\fR
Run in quiet mode when SoX wouldn't otherwise do so;
this is the opposite of the \fB\-S\fR option.
.TP
\fB\-\-replay\-gain track\fR\^|\^\fBalbum\fR\^|\^\fBoff\fR
Select whether or not to apply replay-gain adjustment to input files.
The default is
.B off
for
.B sox
and
.BR rec ,
.B album
for
.B play
where (at least) the first two input files are tagged with the same Artist and
Album names, and
.B track
for
.B play
otherwise.
.TP
\fB\-S\fR, \fB\-\-show\-progress\fR
Display input file format/header information and input file(s)
processing progress in terms of elapsed/remaining time and percentage
complete.
Also displays the number of samples written to the output file, a VU meter,
and an indication if clipping has occurred.
The VU meter shows up to two channels and is calibrated for digital
audio as follows:
.TS
center box;
cI lI lI
cI lI lI
r l l.
dB FSD Display
>= (right channel)
\-25 \-
\-23 T{
=
T}
\-21 =\-
\-19 ==
\-17 ==\-
\-15 ===
\-13 ===\-
\-11 ====
\-9 ====\-
\-7 =====
\-5 =====\-
\-3 ======
\-1 =====! `In the red'
.TE
.SP
A three-second peak-held value of headroom in dBs will be shown to the right
of the meter if this is below 6dB.
.SP
This option is enabled by default when using
SoX to play or record audio.
.TP
\fB\-\-version\fR
Show version number and exit.
.IP \fB\-V\fB[\fIlevel\fB]\fP
Set verbosity.
SoX prints messages to the console (stderr) according to the following
verbosity levels:
.IP
.RS
.IP 0
No messages are printed at all; use the exit status to determine
if an error has occurred.
.IP 1
Only error messages are printed. These are generated if
SoX cannot complete the requested commands.
.IP 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.
.IP 3
Descriptions of
SoX's processing phases are also printed.
Useful for seeing exactly how
SoX is mangling your audio.
.IP "4 and above"
Messages to help with debugging
SoX are also printed.
.RE
.IP
By default, the verbosity level is set to 2. Each occurrence of the \fB\-V\fR
option increases the verbosity level by 1. Alternatively, the verbosity
level can be set to an absolute number by specifying it immediately after
the
.B \-V
e.g.
.B \-V0
sets it to 0.
.IP
.SS Input File Options
These options apply only to input files and may precede only input
filenames on the command line.
.TP
\fB\-v\fR, \fB\-\-volume\fR \fIFACTOR\fR
Adjust volume by a factor of \fIFACTOR\fR.
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.
.SP
See also the \fBstat\fR 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.
.SP
See also \fBInput File Balancing\fR above.
.SS 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.
.TP
\fB\-c\fR, \fB\-\-channels\fR \fICHANNELS\fR
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
.B mixer
effect must be used. If the
.B mixer
effect is not specified on the
command line it will be invoked internally with default parameters.
.TP
\fB\-r, \fB\-\-rate\fR \fIRATE\fR[\fBk\fR]
Gives the sample rate in Hz (or kHz if appended with `k') 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.
.SP
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 the \fBrate\fR effect will
be chosen by default.
.TP
\fB\-t\fR, \fB\-\-type\fR \fIfile-type\fR
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.
.SP
The \fB\-t\fR 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.
.SP
See
.BR soxformat (7)
for a list of supported file types.
.PP
\fB\-L\fR, \fB\-\-endian little\fR
.br
\fB\-B\fR, \fB\-\-endian big\fR
.br
\fB\-x\fR, \fB\-\-endian swap\fR
.if t .sp -.5
.if n .sp -1
.TP
\
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.
.SP
.B 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:
.EX
sox -B audio.s2 trimmed.s2 trim 2
.EE
trimmed.s2 will be created as little-endian;
.EX
sox -B audio.s2 -B trimmed.s2 trim 2
.EE
must be used to preserve big-endianness in the output file.
.SP
The
.B \-V
option can be used to check the selected orderings.
.TP
\fB\-N\fR, \fB\-\-reverse\-nibbles\fR
Specifies that the nibble ordering (i.e. the 2 halves of a byte) of the samples should be reversed;
sometimes useful with ADPCM-based formats.
.SP
.B N.B.
See also N.B. in section on
.B \-x
above.
.TP
\fB\-X\fR, \fB\-\-reverse\-bits\fR
Specifies that the bit ordering of the samples should be reversed;
sometimes useful with a few (mostly headerless) formats.
.SP
.B N.B.
See also N.B. in section on
.B \-x
above.
.TP
\fB\-s\fR\^/\fB\-u\fR\^/\fB\-U\fR\^/\fB\-A\fR\^/\fB\-a\fR\^/\fB\-i\fR\^/\fB\-g\fR\^/\fB\-f\fR
The audio data encoding is signed linear (2's complement),
unsigned linear, \(*m-law (logarithmic), A-law (logarithmic),
ADPCM, IMA-ADPCM, GSM, or floating-point.
.SP
\(*m-law (or mu-law) and A-law are the U.S. and
international standards for logarithmic telephone audio compression.
When uncompressed \(*m-law has roughly the precision of 14-bit PCM audio
and A-law has roughly the precision of 13-bit PCM audio.
.SP
A-law and \(*m-law are sometimes encoded using reversed bit-ordering
(i.e. MSB becomes LSB). If you need this support then you can use the
.B \-X
option or the pseudo
file types of `.la' and `.lu' to inform SoX of the encoding. See
supported file types for more information.
.SP
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 \fB\-a\fR flag has different meanings
in different file handlers. In \fB.wav\fR 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.
.SP
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.
.TP
\fB\-1\fR\^/\fB\-2\fR\^/\fB\-3\fR\^/\fB\-4\fR\^/\fB\-8\fR
The sample datum size is 1, 2, 3, 4, or 8 bytes; i.e. 8, 16, 24, 32, or 64 bits.
.SS Output File Format Options
These options apply only to the output file and may precede only the output
filename on the command line.
.TP
\fB\-\-add\-comment \fITEXT\fR
Append a comment in the output file header (where applicable).
.TP
\fB\-\-comment \fITEXT\fR
Specify the comment text to store in the output file header (where
applicable).
.SP
SoX will provide a default comment if this option (or
.BR \-\-comment\-file )
is not given; to specify that no comment should be stored in the output file,
use
.B "\-\-comment \(dq\(dq" .
.TP
\fB\-\-comment\-file \fIFILENAME\fR
Specify a file containing the comment text to store in the output
file header (where applicable).
.TP
\fB\-C\fR, \fB\-\-compression\fR \fIFACTOR\fR
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
.BR soxformat (7)
for more information.
.SH DIAGNOSTICS
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 processing.
.SH BUGS
Please report any bugs found in this version of SoX to the mailing list
(sox-users@lists.sourceforge.net).
.SH SEE ALSO
.BR soxi (1),
.BR soxexam (7),
.BR soxformat (7),
.BR soxeffect (7),
.BR gnuplot (1),
.BR octave (1),
.BR wget (1),
.BR libsox (3)
.SP
The SoX web site at http://sox.sourceforge.net
.SH LICENSE
Copyright 1991 Lance Norskog and Sundry Contributors.
Copyright 1998\-2007 by Chris Bagwell and SoX Contributors.
.SP
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 later version.
.SP
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.
.SH AUTHORS
Chris Bagwell (cbagwell@users.sourceforge.net).
Other authors and contributors are listed in the AUTHORS file that
is distributed with the source code.