ref: f867f34ca211c5ff417ebd673cb0788b83bf23d5
dir: /sox.txt/
SoX(1) Sound eXchange SoX(1)
NAME
sox - Sound eXchange : universal sound sample translator
SYNOPSIS
sox infile1 [ infile2 ... ] outfile
sox [ global options ] [ format options ] infile1
[ [ format options ] infile2 ... ] [ format options ] outfile
[ effect [ effect options ] ... ]
soxmix infile1 infile2 [ infile3 ... ] outfile
soxmix [ global options ] [ format options ] infile1
[ format options ] infile2
[ [ format options ] infile3 ... ]
[ format options ] outfile
[ effect [ effect options ] ... ]
DESCRIPTION
SoX is a command line program that can convert most popular audio files
to most other popular audio file formats. It can optionally change the
audio sample data type and apply one or more sound effects to the file
during this translation.
If more than one input file is specified then they are concatenated
into the output file. In this case, it has a restriction that all
input files must be of the same data type and sample rates.
soxmix is functionally the same as the command line program sox except
that it takes two or more files as input and mixes the audio together
to produce a single file as output. It has a restriction that all
input files must be of the same data type and sample rates.
There are two types of audio file formats that SoX can work with. The
first are self-describing file formats. These contain a header that
completely describe the characteristics of the audio data that follows.
The second type are header-less data, or sometimes called raw data. A
user must pass enough information to SoX on the command line so that it
knows what type of data it contains.
Audio data can usually be totally described by four characteristics:
rate The sample rate is in samples per second. For example, CD
sample rates are at 44100.
data size The precision the data is stored in. Most popular are 8-bit
bytes or 16-bit words.
data encoding
What encoding the data type uses. Examples are u-law, ADPCM,
or signed linear data.
channels How many channels are contained in the audio data. Mono and
Stereo are the two most common.
Please refer to the soxexam(1) manual page for a long description with
examples on how to use SoX with various types of file formats.
OPTIONS
The option syntax is a little grotty, but in essence:
sox file.au file.wav
translates a sound file in SUN Sparc .AU format into a Microsoft .WAV
file, while
sox -v 0.5 file.au -r 12000 file.wav mask
does the same format translation but also lowers the amplitude by 1/2,
changes the sampling rate to 12000 hertz, and applies the mask sound
effect to the audio data.
The following will mix two sound files together to to produce a single
sound file.
soxmix music.wav voice.wav mixed.wav
Filenames:
SoX can be used as a part of pipe operations by using the special file-
names of "-". If specified as an input name, it will read data from
stdin. If specified as an output name, it will send data to stdout.
Global options:
-h Print version number and usage information.
--help Same as -h
--help-effect=name
Prints usage information on the specifed effect. The name
all can be used to disable usage on all effects.
-p Run in preview mode and run fast. This will somewhat speed
up SoX when the output format has a different number of chan-
nels and a different rate than the input file. Currently,
this defaults to using the rate effect instead of the resam-
ple effect for sample rate changes.
-q Run in quite mode when SoX wouldn’t otherwise do that.
Inverse of -S option.
-S Print status while processing audio data. Tells how much of
audio data has been processed in terms of audio running time
instead of samples.
--version Print version number and exit.
-V Print a description of processing phases. Useful for figur-
ing out exactly how SoX
is mangling your sound samples.
Format options:
Format options effect the input or output file that they immediately
precede.
Self describing input files can obtain all the format information
directly from the header and so don’t generally need format options.
Headerless input files lack this information and so format options must
be used to inform SoX of the file’s data type, sample rate, and number
of channels.
By default, SoX attempts to write audio data using the same data type,
sample rate, and channel count as the input data. If the user wants
the output file to be of a different format then format options can be
used to specify the differences.
If an output file format doesn’t support the same data type, sample
rate, or channel count as the input file format, then SoX will auto
select the closest values it does support so that the user does not
have to specify these format change options manually.
-c channels
The number of sound channels in the data file. This may be
1, 2, or 4; for mono, stereo, or quad sound data. 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 num-
ber of channels then the avg effect must be used. If the avg
effect is not specified on the command line it will be
invoked internally with default parameters.
-e When specified after the last input filename (so that it
applies to the output file) it allows you to avoid giving an
output filename and will not produce an output file. It will
apply any specified effects to the input file. This is
mainly useful with the stat effect but can be used.
-r rate Gives the sample rate in Hertz of the file. To cause the
output file to have a different sample rate than the input
file, include this option as a part of the output format
options.
If the input and output files have different rates then a
sample rate change effect must be ran. Since SoX has multi-
ple 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 filetype
gives the file type of the sound sample file. Useful when
file extension is not standard or can not be determeind by
looking at the header of the file. See the section FILE
TYPES for a list of supported file types.
-v volume Change amplitude (floating point); less than 1.0 decreases,
greater than 1.0 increases. May use a negative number to
invert the phase of the audio data. It is interesting to
note that we perceive volume logarithmically but this adjusts
the amplitude linearly.
As with other format options, the volume option effects the
file its specified with. This is useful whe processing muti-
ple input files as the volume adjustment can be specified for
each input file or just once to adjust the output file. This
can be compared to an audio mixer were you can control the
volume of each input as well as a master volume (output
side).
soxmix defaults the value of the -v option for each input
file to 1/input_file_count. This means if your mixing two
input files together then each input file’s volume is
adjusted by 0.5. This is done to prevent clipping of audio
data during the mixing operation. Users will most likely not
be happy with this large of a volume adjustment and can spec-
ify the -v option to override this default value.
Note: For the non-mixing case, see the stat effect for infor-
mation on finding the maximum volume adjustment that can be
done with this option without causing audio data to be
clipped.
-x The sample data is in XINU format; that is, it comes from a
machine with the opposite word order than yours and must be
swapped according to the word-size given above. Only 16-bit
and 32-bit integer data may be swapped. Machine-format
floating-point data is not portable.
-s/-u/-U/-A/-a/-i/-g/-f
The sample data encoding is signed linear (2’s complement),
unsigned linear, u-law (logarithmic), A-law (logarithmic),
ADPCM, IMA_ADPCM, GSM, or Floating-point.
U-law (actually shorthand for mu-law) and A-law are the U.S.
and international standards for logarithmic telephone sound
compression. When uncompressed u-law has roughly the preci-
sion of 14-bit PCM audio and A-law has roughly the precision
of 13-bit PCM audio.
A-law and u-law data is sometimes encoded using a reversed
bit-ordering (ie. MSB becomes LSB). Internally, SoX under-
stands how to work with this encoding but there is currently
no command line option to specify it. If you need this sup-
port then you can use the psuedo file types of ".la" and
".lu" to inform sox of the encoding. See supported file
types for more information.
ADPCM is a form of sound compression that has a good compro-
mise between good sound quality and fast encoding/decoding
time. It is used for telephone sound compression and places
were full fidelity is not as important. When uncompressed it
has roughly the precision of 16-bit PCM audio. Popular ver-
sion 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 a standard used for telephone sound compression in
European countries and its gaining popularity because of its
quality. It usually is CPU intensive to work with GSM audio
data.
-b/-w/-l/-d
The sample data size is in bytes, 16-bit words, 32-bit long
words, or 64-bit double long (long long) words.
FILE TYPES
SoX attempts to determine the file type of input files automatically by
looking at the header of the audio file. When it is unable to detect
the file type or if its an output file then it uses the file extension
of the file to determine what type of file format handler to use. This
can be overridden by specifying the "-t" option on the command line.
The input and output files may be read from standard in and out. This
is done by specifying ’-’ as the filename.
File formats which have headers are checked, if that header doesn’t
seem right, the program exits with an appropriate message.
The following file formats are supported:
.8svx Amiga 8SVX musical instrument description format.
.aiff AIFF files used on Apple IIc/IIgs and SGI. Note: the AIFF
format supports only one SSND chunk. It does not support
multiple sound chunks, or the 8SVX musical instrument
description format. AIFF files are multimedia archives and
can have multiple audio and picture chunks. You may need a
separate archiver to work with them.
.alsa ALSA /dev/snd/pcmCxDxp device driver
This is a pseudo-file type and can be optionally compiled
into SoX. Run sox -h to see if you have support for this
file type. When this driver is used it allows you to open up
the ALSA /dev/snd/pcmCxDxp file and configure it to use the
same data format as passed in to SoX. It works for both
playing and recording sound samples. When playing sound
files it attempts to set up the ALSA driver to use the same
format as the input file. It is suggested to always override
the output values to use the highest quality samples your
sound card can handle. Example: sox infile -t alsa -w -s
/dev/snd/pcmC0D0p
.au SUN Microsystems AU files. There are apparently many types
of .au files; DEC has invented its own with a different magic
number and word order. The .au handler can read these files
but will not write them. Some .au files have valid AU head-
ers and some do not. The latter are probably original SUN u-
law 8000 hz samples. These can be dealt with using the .ul
format (see below).
.avr Audio Visual Research
The AVR format is produced by a number of commercial packages
on the Mac.
.cdr CD-R
CD-R files are used in mastering music on Compact Disks. The
audio data on a CD-R disk is a raw audio file with a format
of stereo 16-bit signed samples at a 44khz sample rate.
There is a special blocking/padding oddity at the end of the
audio file and is why it needs its own handler.
.cvs Continuously Variable Slope Delta modulation
Used to compress speech audio for applications such as voice
mail.
.dat Text Data files
These files contain a textual representation of the sample
data. There is one line at the beginning that contains the
sample rate. Subsequent lines contain two numeric data
items: the time since the beginning of the first sample and
the sample value. Values are normalized so that the maximum
and minimum are 1.00 and -1.00. This file format can be used
to create data files for external programs such as FFT ana-
lyzers or graph routines. SoX can also convert a file in
this format back into one of the other file formats.
.gsm GSM 06.10 Lossy Speech Compression
A standard for compressing speech which is used in the Global
Standard for Mobil telecommunications (GSM). Its good for
its purpose, shrinking audio data size, but it will introduce
lots of noise when a given sound sample is encoded and
decoded multiple times. This format is used by some voice
mail applications. It is rather CPU intensive.
GSM in SoX is optional and requires access to an external GSM
library. To see if there is support for gsm run sox -h and
look for it under the list of supported file formats.
.hcom Macintosh HCOM files. These are (apparently) Mac FSSD files
with some variant of Huffman compression. The Macintosh has
wacky file formats and this format handler apparently doesn’t
handle all the ones it should. Mac users will need your
usual arsenal of file converters to deal with an HCOM file
under Unix or DOS.
.maud An Amiga format
An IFF-conform sound file type, registered by MS MacroSystem
Computer GmbH, published along with the "Toccata" sound-card
on the Amiga. Allows 8bit linear, 16bit linear, A-Law, u-law
in mono and stereo.
.mp3 MP3 Compressed Audio
MP3 audio files come from the MPEG standards for audio and
video compression. They are a lossy compression format that
achieves good compression rates with a minimum amount of
quality loss. Also see Ogg Vorbis for a similar format. MP3
support in SoX is optional and requires access to either or
both the external libmad and libmp3lame libraries. To see if
there is support for Mp3 run sox -h and look for it under the
list of supported file formats as "mp3".
.nul Null file handler. This is a fake file hander that act as if
its reading a stream of 0’s from a while or fake writing out-
put to a file. This is not a very useful file handler in
most cases. It might be useful in some scripts were you do
not want to read or write from a real file but would like to
specify a filename for consistency.
.ogg Ogg Vorbis Compressed Audio.
Ogg Vorbis is a open, patent-free CODEC designed for com-
pressing music and streaming audio. It is similar to MP3,
VQF, AAC, and other lossy formats. SoX can decode all types
of Ogg Vorbis files, but can only encode at 128 kbps. Decod-
ing is somewhat CPU intensive and encoding is very CPU inten-
sive.
Ogg Vorbis in SoX is optional and requires access to external
Ogg Vorbis libraries. To see if there is support for Ogg
Vorbis run sox -h and look for it under the list of supported
file formats as "vorbis".
ossdsp OSS /dev/dsp device driver
This is a pseudo-file type and can be optionally compiled
into SoX. Run sox -h to see if you have support for this
file type. When this driver is used it allows you to open up
the OSS /dev/dsp file and configure it to use the same data
format as passed in to SoX. It works for both playing and
recording sound samples. When playing sound files it
attempts to set up the OSS driver to use the same format as
the input file. It is suggested to always override the out-
put values to use the highest quality samples your sound card
can handle. Example: sox infile -t ossdsp -w -s /dev/dsp
.prc Psion record.app
Used in some Psion devices for System alarms. This format is
newer then the .wve format that is used in some Psion
devices.
.sf IRCAM Sound Files.
Sound Files are used by academic music software such as the
CSound package, and the MixView sound sample editor.
.sph
SPHERE (SPeech HEader Resources) is a file format defined by
NIST (National Institute of Standards and Technology) and is
used with speech audio. SoX can read these files when they
contain u-law and PCM data. It will ignore any header infor-
mation that says the data is compressed using shorten com-
pression and will treat the data as either u-law or PCM.
This will allow SoX and the command line shorten program to
be ran together using pipes to uncompress the data and then
pass the result to SoX for processing.
.smp Turtle Beach SampleVision files.
SMP files are for use with the PC-DOS package SampleVision by
Turtle Beach Softworks. This package is for communication to
several MIDI samplers. All sample rates are supported by the
package, although not all are supported by the samplers them-
selves. Currently loop points are ignored.
.snd
Under DOS this file format is the same as the .sndt format.
Under all other platforms it is the same as the .au format.
.sndt SoundTool files.
This is an older DOS file format.
sunau Sun /dev/audio device driver
This is a pseudo-file type and can be optionally compiled
into SoX. Run sox -h to see if you have support for this
file type. When this driver is used it allows you to open up
a Sun /dev/audio file and configure it to use the same data
type as passed in to SoX. It works for both playing and
recording sound samples. When playing sound files it
attempts to set up the audio driver to use the same format as
the input file. It is suggested to always override the out-
put values to use the highest quality samples your hardware
can handle. Example: sox infile -t sunau -w -s /dev/audio or
sox infile -t sunau -U -c 1 /dev/audio for older sun equip-
ment.
.txw Yamaha TX-16W sampler.
A file format from a Yamaha sampling keyboard which wrote
IBM-PC format 3.5" floppies. Handles reading of files which
do not have the sample rate field set to one of the expected
by looking at some other bytes in the attack/loop length
fields, and defaulting to 33kHz if the sample rate is still
unknown.
.vms More info to come.
Used to compress speech audio for applications such as voice
mail.
.voc Sound Blaster VOC files.
VOC files are multi-part and contain silence parts, looping,
and different sample rates for different chunks. On input,
the silence parts are filled out, loops are rejected, and
sample data with a new sample rate is rejected. Silence with
a different sample rate is generated appropriately. On out-
put, silence is not detected, nor are impossible sample
rates. Note, this version now supports playing VOC files
with multiple blocks and supports playing files containing u-
law and A-law samples.
vorbis See .ogg format.
.vox A headerless file of Dialogic/OKI ADPCM audio data commonly
comes with the extension .vox. This ADPCM data has 12-bit
precision packed into only 4-bits.
.wav Microsoft .WAV RIFF files.
These appear to be very similar to IFF files, but not the
same. They are the native sound file format of Windows.
(Obviously, Windows was of such incredible importance to the
computer industry that it just had to have its own sound file
format.)
Normally .wav files have all formatting information in their
headers, and so do not need any format options specified for
an input file. If any are, they will override the file
header, and you will be warned to this effect. You had bet-
ter know what you are doing! Output format options will cause
a format conversion, and the .wav will written appropriately.
SoX currently can read PCM, ULAW, ALAW, MS ADPCM, and IMA (or
DVI) ADPCM. It can write all of these formats including the
ADPCM encoding. Big endian versions of RIFF files, called
RIFX, can also be read and written. To write a RIFX file,
use the -x option with the output file options.
.wve Psion 8-bit A-law
These are 8-bit A-law 8khz sound files used on the Psion
palmtop portable computer.
.raw Raw files (no header).
The sample rate, size (byte, word, etc), and encoding
(signed, unsigned, etc.) of the sample file must be given.
The number of channels defaults to 1.
.ub, .sb, .uw, .sw, .ul, .al, .lu, .la, .sl
These are several suffices which serve as a shorthand for raw
files with a given size and encoding. Thus, ub, sb, uw, sw,
ul, al, lu, la and sl correspond to "unsigned byte", "signed
byte", "unsigned word", "signed word", "u-law" (byte), "A-
law" (byte), inverse bit order "u-law", inverse bit order "A-
law", and "signed long". The sample rate defaults to 8000 hz
if not explicitly set, and the number of channels defaults to
1. There are lots of Sparc samples floating around in u-law
format with no header and fixed at a sample rate of 8000 hz.
(Certain sound management software cheerfully ignores the
headers.) Similarly, most Mac sound files are in unsigned
byte format with a sample rate of 11025 or 22050 hz.
.auto This is a ‘‘meta-type’’ and is the default file type if the
user does not specify one. This file type attempts to guess
the real type by looking for magic words in the header. If
the type can’t be guessed, the program exits with an error
message. The input must be a plain file, not a pipe. This
type can’t be used for output files.
EFFECTS
Multiple effects may be applied to the audio data by specifying them
one after another at the end of the command line.
avg [ -l | -r | -f | -b | -1 | -2 | -3 | -4 | n,n,...,n ]
Reduce the number of channels by averaging the samples, or
duplicate channels to increase the number of channels. This
effect is automatically used when the number of input chan-
nels differ from the number of output channels. When reduc-
ing the number of channels it is possible to manually specify
the avg effect and use the -l, -r, -f, -b, -1, -2, -3, -4,
options to select only the left, right, front, back chan-
nel(s) or specific channel for the output instead of averag-
ing the channels. The -l, and -r options will do averaging
in quad-channel files so select the exact channel to prevent
this.
The avg effect can also be invoked with up to 16 double-pre-
cision numbers, seperated by commas, which specify the pro-
portion (0.0 = 0% and 1.0 = 100%) of each input channel that
is to be mixed into each output channel. In two-channel
mode, 4 numbers are given: l->l, l->r, r->l, and r->r,
respectively. In four-channel mode, the first 4 numbers give
the proportions for the left-front output channel, as fol-
lows: lf->lf, rf->lf, lb->lf, and rb->rf. The next 4 give
the right-front output in the same order, then left-back and
right-back.
It is also possible to use the 16 numbers to expand or reduce
the channel count; just specify 0 for unused channels.
Finally, certain reduced combination of numbers can be
specified for certain input/output channel combinations.
In Ch Out Ch Num Mappings
_____ ______ ___ _____________________________
2 1 2 l->l, r->l
2 2 1 adjust balance
4 1 4 lf->l, rf->l, lb->l, rb-l
4 2 2 lf->l&rf->r, lb->l&rb->r
4 4 1 adjust balance
4 4 2 front balance, back balance
band [ -n ] center [ width ]
Apply a band-pass filter. The frequency response drops loga-
rithmically around the center frequency. The width gives the
slope of the drop. The frequencies at center + width and
center - width will be half of their original amplitudes.
Band defaults to a mode oriented to pitched signals, i.e.
voice, singing, or instrumental music. The -n (for noise)
option uses the alternate mode for un-pitched signals. Warn-
ing: -n introduces a power-gain of about 11dB in the filter,
so beware of output clipping. Band introduces noise in the
shape of the filter, i.e. peaking at the center frequency and
settling around it. See filter for a bandpass effect with
steeper shoulders.
bandpass frequency bandwidth
Butterworth bandpass filter. Description coming soon!
bandreject frequency bandwidth
Butterworth bandreject filter. Description coming soon!
chorus gain-in gain-out delay decay speed depth
-s | -t [ delay decay speed depth -s | -t ... ]
Add a chorus to a sound sample. Each quadtuple
delay/decay/speed/depth gives the delay in milliseconds and
the decay (relative to gain-in) with a modulation speed in Hz
using depth in milliseconds. The modulation is either sinu-
soidal (-s) or triangular (-t). Gain-out is the volume of
the output.
compand attack1,decay1[,attack2,decay2...]
in-dB1,out-dB1[,in-dB2,out-dB2...]
[gain [initial-volume [delay ] ] ]
Compand (compress or expand) the dynamic range of a sample.
The attack and decay time specify the integration time over
which the absolute value of the input signal is integrated to
determine its volume; attacks refer to increases in volume
and decays refer to decreases. Where more than one pair of
attack/decay parameters are specified, each channel is
treated separately and the number of pairs must agree with
the number of input channels. The second parameter is a list
of points on the compander’s transfer function specified in
dB relative to the maximum possible signal amplitude. The
input values must be in a strictly increasing order but the
transfer function does not have to be monotonically rising.
The special value -inf may be used to indicate that the input
volume should be associated output volume. The points
-inf,-inf and 0,0 are assumed; the latter may be overridden,
but the former may not.
The third (optional) parameter is a post-processing gain in
dB which is applied after the compression has taken place;
the fourth (optional) parameter is an initial volume to be
assumed for each channel when the effect starts. This per-
mits the user to supply a nominal level initially, so that,
for example, a very large gain is not applied to initial sig-
nal levels before the companding action has begun to operate:
it is quite probable that in such an event, the output would
be severely clipped while the compander gain properly adjusts
itself.
The fifth (optional) parameter is a delay in seconds. The
input signal is analyzed immediately to control the compan-
der, but it is delayed before being fed to the volume
adjuster. Specifying a delay approximately equal to the
attack/decay times allows the compander to effectively oper-
ate in a "predictive" rather than a reactive mode.
copy Copy the input file to the output file. This is the default
effect if both files have the same sampling rate.
dcshift shift [ limitergain ]
DC Shift the audio data, with basic linear amplitude formula.
This is most useful if your audio data tends to not be cen-
tered around a value of 0. Shifting it back will allow you
to get the most volume adjustments without clipping audio
data.
The first option is the dcshift value. It is a floating
point number that indicates the amount to shift.
An option limtergain value can be specified as well. It
should have a value much less then 1.0 and is used only on
peaks to prevent clipping.
deemph Apply a treble attenuation shelving filter to samples in
audio cd format. The frequency response of pre-emphasized
recordings is rectified. The filtering is defined in the
standard document ISO 908.
earwax Makes sound easier to listen to on headphones. Adds audio-
cues to samples in audio cd format so that when listened to
on headphones the stereo image is moved from inside your head
(standard for headphones) to outside and in front of the lis-
tener (standard for speakers). See
www.geocities.com/beinges for a full explanation.
echo gain-in gain-out delay decay [ delay decay ... ]
Add echoing to a sound sample. Each delay/decay part gives
the delay in milliseconds and the decay (relative to gain-in)
of that echo. Gain-out is the volume of the output.
echos gain-in gain-out delay decay [ delay decay ... ]
Add a sequence of echos to a sound sample. Each delay/decay
part gives the delay in milliseconds and the decay (relative
to gain-in) of that echo. Gain-out is the volume of the out-
put.
fade [ type ] fade-in-length
[ stop-time [ fade-out-length ] ]
Add a fade effect to the beginning, end, or both of the audio
data.
For fade-ins, this starts from the first sample and ramps the
volume of the audio from 0 to full volume over fade-in-length
seconds. Specify 0 seconds if no fade-in is wanted.
For fade-outs, the audio data will be truncated at the stop-
time and the volume will be ramped from full volume down to 0
starting at fade-out-length seconds before the stop-time. If
fade-out-length is not specified, it defaults to the same
value as fade-in-length. No fade-out is performed if the
stop-time is not specified.
All times can be specified in either periods of time or sam-
ple counts. To specify time periods use the format
hh:mm:ss.frac format. To specify using sample counts, spec-
ify the number of samples and append the letter ’s’ to the
sample count (for example 8000s).
An optional type can be specified to change the type of enve-
lope. Choices are q for quarter of a sinewave, h for half a
sinewave, t for linear slope, l for logarithmic, and p for
inverted parabola. The default is a linear slope.
filter [ low ]-[ high ] [ window-len [ beta ] ]
Apply a Sinc-windowed lowpass, highpass, or bandpass filter
of given window length to the signal. low refers to the fre-
quency of the lower 6dB corner of the filter. high refers to
the frequency of the upper 6dB corner of the filter.
A lowpass filter is obtained by leaving low unspecified, or
0. A highpass filter is obtained by leaving high unspeci-
fied, or 0, or greater than or equal to the Nyquist fre-
quency.
The window-len, if unspecified, defaults to 128. Longer win-
dows give a sharper cutoff, smaller windows a more gradual
cutoff.
The beta, if unspecified, defaults to 16. This selects a
Kaiser window. You can select a Nuttall window by specifying
anything <= 2.0 here. For more discussion of beta, look
under the resample effect.
flanger gain-in gain-out delay decay speed < -s | -t >
Add a flanger to a sound sample. Each triple
delay/decay/speed gives the delay in milliseconds and the
decay (relative to gain-in) with a modulation speed in Hz.
The modulation is either sinodial (-s) or triangular (-t).
Gain-out is the volume of the output.
highp frequency
Apply a single pole recursive high-pass filter. The fre-
quency response drops logarithmically with I frequency in the
middle of the drop. The slope of the filter is quite gentle.
See filter for a highpass effect with sharper cutoff.
highpass frequency
Butterworth highpass filter. Description coming soon!
lowp frequency
Apply a single pole recursive low-pass filter. The frequency
response drops logarithmically with frequency in the middle
of the drop. The slope of the filter is quite gentle. See
filter for a lowpass effect with sharper cutoff.
lowpass frequency
Butterworth lowpass filter. Description coming soon!
mask Add "masking noise" to signal. This effect deliberately adds
white noise to a sound in order to mask quantization effects,
created by the process of playing a sound digitally. It
tends to mask buzzing voices, for example. It adds 1/2 bit
of noise to the sound file at the output bit depth.
mcompand "attack1,decay1[,attack2,decay2...]
in-dB1,out-dB1[,in-dB2,out-dB2...]
[gain [initial-volume [delay ] ] ]" xover_freq
Multi-band compander is similar to the single band compander
but the audio file is first divided up into bands and then
the compander is ran on each band. See the compand effect
for definition of its options. Compand options are specified
between double quotes and the crossover frequency for that
band is specefied seperately with xover_fre. This can be
repeated multiple times to create multiple bands.
noiseprof [profile-file]
noisered profile-file [threshold]
Noise reduction filter with profiling. This filter is moder-
ately effective at removing consistent background noise such
as hiss or hum. To use it, first run the noiseprof effect on
a section of silence (that is, a section which contains noth-
ing but noise). The noiseprof effect will print a noise pro-
file to profile-file, or to stdout if no profile-file is
specified. If there is sound output on stdout then the pro-
file will instead be directed to stderr.
To actually remove the noise, run SoX again with the noisered
filter. The filter needs one argument, profile-file, which
contains the noise profile from noiseprof. thershold speci-
fies how much noise should be removed, and may be between 0
and 1 with a default of 0.5. Higher values will remove more
noise but present a greater possibility of distorting the
desired audio signal. Experiment with different threshold
values to find the optimal one for your sample.
pan direction
Pan the sound of an audio file from one channel to another.
This is done by changing the volume of the input channels so
that it fades out on one channel and fades-in on another. If
the number of input channels is different then the number of
output channels then this effect tries to intelligently han-
dle this. For instance, if the input contains 1 channel and
the output contains 2 channels, then it will create the miss-
ing channel itself. The direction is a value from -1.0 to
1.0. -1.0 represents far left and 1.0 represents far right.
Numbers in between will start the pan effect without totally
muting the opposite channel.
phaser gain-in gain-out delay decay speed < -s | -t >
Add a phaser to a sound sample. Each triple
delay/decay/speed gives the delay in milliseconds and the
decay (relative to gain-in) with a modulation speed in Hz.
The modulation is either sinodial (-s) or triangular (-t).
The decay should be less than 0.5 to avoid feedback. Gain-
out is the volume of the output.
pick [ -1 | -2 | -3 | -4 | -l | -r | -f | -b ]
Pick a subset of channels to be copied into the output file.
This effect is just an alias of the "avg" effect but is left
here for historical reasons.
pitch shift [ width interpole fade ]
Change the pitch of file without affecting its duration by
cross-fading shifted samples. shift is given in cents. Use a
positive value to shift to treble, negative value to shift to
bass. Default shift is 0. width of window is in ms. Default
width is 20ms. Try 30ms to lower pitch, and 10ms to raise
pitch. interpole option, can be "cubic" or "linear". Default
is "cubic". The fade option, can be "cos", "hamming", "lin-
ear" or "trapezoid". Default is "cos".
polyphase [ -w < nut / ham > ]
[ -width < long / short / # > ]
[ -cutoff # ]
Translate input sampling rate to output sampling rate via
polyphase interpolation, a DSP algorithm. This method is
slow and uses lots of RAM, but gives much better results than
rate.
-w < nut / ham > : select either a Nuttal (~90 dB stopband)
or Hamming (~43 dB stopband) window. Default is nut.
-width long / short / # : specify the (approximate) width of
the filter. long is 1024 samples; short is 128 samples.
Alternatively, an exact number can be used. Default is long.
The short option is not recommended, as it produces poor
quality results.
-cutoff # : specify the filter cutoff frequency in terms of
fraction of frequency bandwidth, also know as the Nyquist
frequency. Please see the resample effect for further infor-
mation on Nyquist frequency. If upsampling, then this is the
fraction of the original signal that should go through. If
downsampling, this is the fraction of the signal left after
downsampling. Default is 0.95. Remember that this is a
float.
rate Translate input sampling rate to output sampling rate via
linear interpolation to the Least Common Multiple of the two
sampling rates. This is the default effect if the two files
have different sampling rates and the preview options was
specified. This is fast but noisy: the spectrum of the orig-
inal sound will be shifted upwards and duplicated faintly
when up-translating by a multiple.
Lerp-ing is acceptable for cheap 8-bit sound hardware, but
for CD-quality sound you should instead use either resample
or polyphase. If you are wondering which rate changing
effects to use, you will want to read a detailed analysis of
all of them at http://leute.server.de/wilde/resample.html
repeat count
Repeats the audio data count times. Requires disk space to
store the data to be repeated.
resample [ -qs | -q | -ql ] [ rolloff [ beta ] ]
Translate input sampling rate to output sampling rate via
simulated analog filtration. This method is slower than
rate, but gives much better results.
By default, linear interpolation is used, with a window width
about 45 samples at the lower of the two rate. This gives an
accuracy of about 16 bits, but insufficient stopband rejec-
tion in the case that you want to have rolloff greater than
about 0.80 of the Nyquist frequency.
The -q* options will change the default values for rolloff
and beta as well as use quadratic interpolation of filter
coefficients, resulting in about 24 bits precision. The -qs,
-q, or -ql options specify increased accuracy at the cost of
lower execution speed. It is optional to specify rolloff and
beta parameters when using the -q* options.
Following is a table of the reasonable defaults which are
built-in to SoX:
Option Window rolloff beta interpolation
------ ------ ------- ---- -------------
(none) 45 0.80 16 linear
-qs 45 0.80 16 quadratic
-q 75 0.875 16 quadratic
-ql 149 0.94 16 quadratic
------ ------ ------- ---- -------------
-qs, -q, or -ql use window lengths of 45, 75, or 149 samples,
respectively, at the lower sample-rate of the two files.
This means progressively sharper stop-band rejection, at pro-
portionally slower execution times.
rolloff refers to the cut-off frequency of the low pass fil-
ter and is given in terms of the Nyquist frequency for the
lower sample rate. rolloff therefore should be something
between 0.0 and 1.0, in practice 0.8-0.95. The defaults are
indicated above.
The Nyquist frequency is equal to (sample rate / 2). Logi-
cally, this is because the A/D converter needs at least 2
samples to detect 1 cycle at the Nyquist frequency. Frequen-
cies higher then the Nyquist will actually appear as lower
frequencies to the A/D converter and is called aliasing.
Normally, A/D converts run the signal through a highpass fil-
ter first to avoid these problems.
Similar problems will happen in software when reducing the
sample rate of an audio file (frequencies above the new
Nyquist frequency can be aliased to lower frequencies).
Therefore, a good resample effect will remove all frequency
information above the new Nyquist frequency.
The rolloff refers to how close to the Nyquist frequency this
cutoff is, with closer being better. When increasing the
sample rate of an audio file you would not expect to have any
frequencies exist that are past the original Nyquist fre-
quency. Because of resampling properties, it is common to
have aliasing data created that is above the old Nyquist fre-
quency. In that case the rolloff refers to how close to the
original Nyquist frequency to use a highpass filter to remove
this false data, with closer also being better.
The beta parameter determines the type of filter window used.
Any value greater than 2.0 is the beta for a Kaiser window.
Beta <= 2.0 selects a Nuttall window. If unspecified, the
default is a Kaiser window with beta 16.
In the case of Kaiser window (beta > 2.0), lower betas pro-
duce a somewhat faster transition from passband to stopband,
at the cost of noticeable artifacts. A beta of 16 is the
default, beta less than 10 is not recommended. If you want a
sharper cutoff, don’t use low beta’s, use a longer sample
window. A Nuttall window is selected by specifying any
’beta’ <= 2, and the Nuttall window has somewhat steeper cut-
off than the default Kaiser window. You will probably not
need to use the beta parameter at all, unless you are just
curious about comparing the effects of Nuttall vs. Kaiser
windows.
This is the default effect if the two files have different
sampling rates. Default parameters are, as indicated above,
Kaiser window of length 45, rolloff 0.80, beta 16, linear
interpolation.
NOTE: -qs is only slightly slower, but more accurate for
16-bit or higher precision.
NOTE: In many cases of up-sampling, no interpolation is
needed, as exact filter coefficients can be computed in a
reasonable amount of space. To be precise, this is done when
input_rate < output_rate
&&
output_rate/gcd(input_rate,output_rate) <= 511
reverb gain-out reverbe-time delay [ delay ... ]
Add reverberation to a sound sample. Each delay is given in
milliseconds and its feedback is depending on the reverb-time
in milliseconds. Each delay should be in the range of half
to quarter of reverb-time to get a realistic reverberation.
Gain-out is the volume of the output.
reverse Reverse the sound sample completely. Included for finding
Satanic subliminals.
silence above_periods [ duration threshold[ d | % ]
[ below_periods duration
threshold[ d | % ]]
Removes silence from the beginning, middle, or end of a sound
file. Silence is anything below a specified threshold.
The above_periods value is used to indicate if sound should
be trimmed at the beginning of the audio file. A value of
zero indicates no silence should be trimmed from the begin-
ning. When specifing an non-zero above_periods, it trims
audio up until it finds non-silence. Normally, when trimming
silence from beginning of audio the above_periods will be 1
but it can be increased to higher values to trim all data up
to a specific count of non-silence periods. For example, if
you had an audio file with two songs that each contained 2
seconds of silence before the song, you could specify an
above_period of 2 to strip out both silence periods and the
first song.
When above_periods is non-zero, you must also specify a dura-
tion and threshold. Duration indications the amount of time
that non-silence must be detected before it stops trimming
data. By increasing the duration, burst of noise can be
treated as silence and trimmed off.
Threshold is used to indicate what sample value you should
treat as silence. For digital audio, a value of 0 may be
fine but for audio recorded from analog, you may wish to
increase ths value to account for background noise.
When optionally trimming silence from the end of a sound
file, you specify a below_periods count. In this case,
below_period means to remove all audio data after silence is
detected. Normally, this will be a value 1 of but it can be
increased to skip over periods of silence that are wanted.
For example, if you have a song with 2 seconds of silence in
the middle and 2 second at the end, you could set
below_period to a value of 2 to skip over the silence in the
middle of the audio file.
For below_periods, duration specifies a period of silence
that must exist before data is not copied any more. By spec-
ifying a higher duration, silence that is wanted can be left
in the audio. For example, if you have a song with an
expected 1 second of silence in the middle and 2 seconds of
silence at the end, a duration of 2 seconds could be used to
skip over the middle silence.
Unfortunetly, you must know the length of the silence at the
end of your audio file to trim off silence reliably. A work
around is to use the silence effect in combination with the
reverse effect. By first reversing the audio, you can use
the above_periods to reliably trim all audio from what looks
like the front of the file. Then reverse the file again to
get back to normal.
To remove silence from the middle of a file, specify a
below_periods that is negative. This value is then treated
as a positive value and is also used to indicate the effect
should restart processing as specified by the above_periods,
making it suitable for removing periods of silence in the
middle of the sound file.
The period counts are in units of samples. Duration counts
may be in the format of hh:mm:ss.frac, or the exact count of
samples. Threshold numbers may be suffixed iwth d, or % to
indicate the value is in decibels or a percentage of maximum
value of the sample value (0% specifies pure digital
silence).
speed [ -c ] factor
Speed up or down the sound, as a magnetic tape with a speed
control. It affects both pitch and time. A factor of 1.0
means no change, and is the default. 2.0 doubles speed, thus
time length is cut by a half and pitch is one octave higher.
0.5 halves speed thus time length doubles and pitch is one
octave lower. If the optional -c parameter is used then the
factor is specified in "cents".
stat [ -s n ] [-rms ] [ -v ] [ -d ]
Do a statistical check on the input file, and print results
on the standard error file. Audio data is passed unmodified
from input to output file unless used along with the -e
option.
The "Volume Adjustment:" field in the statistics gives you
the argument to the -v number which will make the sample as
loud as possible without clipping.
The option -v will print out the "Volume Adjustment:" field’s
value only and return. This could be of use in scripts to
auto convert the volume.
The -s n option is used to scale the input data by a given
factor. The default value of n is the max value of a signed
long variable (0x7fffffff). Internal effects always work
with signed long PCM data and so the value should relate to
this fact.
The -rms option will convert all output average values to
root mean square format.
There is also an optional parameter -d that will print out a
hex dump of the sound file from the internal buffer that is
in 32-bit signed PCM data. This is mainly only of use in
tracking down endian problems that creep in to SoX on cross-
platform versions.
stretch factor [window fade shift fading]
Time stretch file by a given factor. Change duration without
affecting the pitch. factor of stretching: >1.0 lengthen,
<1.0 shorten duration. window size is in ms. Default is
20ms. The fade option, can be "lin". shift ratio, in [0.0
1.0]. Default depends on stretch factor. 1.0 to shorten, 0.8
to lengthen. The fading ratio, in [0.0 0.5]. The amount of a
fade’s default depends on factor and shift.
swap [ 1 2 | 1 2 3 4 ]
Swap channels in multi-channel sound files. Optionally, you
may specify the channel order you would like the output in.
This defaults to output channel 2 and then 1 for stereo and
2, 1, 4, 3 for quad-channels. An interesting feature is that
you may duplicate a given channel by overwriting another.
This is done by repeating an output channel on the command
line. For example, swap 2 2 will overwrite channel 1 with
channel 2’s data; creating a stereo file with both channels
containing the same audio data.
synth [ length ] type mix [ freq [ -freq2 ]
[ off ] [ ph ] [ p1 ] [ p2 ] [ p3 ]
The synth effect will generate various types of audio data.
Although this effect is used to generate audio data, an input
file must be specified. The length of the input audio file
determines the length of the output audio file.
<length> length in sec or hh:mm:ss.frac, 0=inputlength,
default=0
<type> is sine, square, triangle, sawtooth, trapetz, exp,
whitenoise, pinknoise, brownnoise, default=sine
<mix> is create, mix, amod, default=create
<freq> frequency at beginning in Hz, not used for noise..
<freq2> frequency at end in Hz, not used for noise..
<freq/2> can be given as %%n, where ’n’ is the number of half
notes in respect to A (440Hz)
<off> Bias (DC-offset) of signal in percent, default=0
<ph> phase shift 0..100 shift phase 0..2*Pi, not used for
noise..
<p1> square: Ton/Toff, triangle+trapetz: rising slope time
(0..100)
<p2> trapetz: ON time (0..100)
<p3> trapetz: falling slope position (0..100)
trim start [ length ]
Trim can trim off unwanted audio data from the beginning and
end of the audio file. Audio samples are not sent to the
output stream until the start location is reached.
The optional length parameter tells the number of samples to
output after the start sample and is used to trim off the
back side of the audio data. Using a value of 0 for the
start parameter will allow trimming off the back side only.
Both options can be specified using either an amount of time
and an exact count of samples. The format for specifying
lengths in time is hh:mm:ss.frac. A start value of 1:30.5
will not start until 1 minute, thirty and 1/2 seconds into
the audio data. The format for specifying sample counts is
the number of samples with the letter ’s’ appended to it. A
value of 8000s will wait until 8000 samples are read before
starting to process audio data.
vibro speed [ depth ]
Add the world-famous Fender Vibro-Champ sound effect to a
sound sample by using a sine wave as the volume knob. Speed
gives the Hertz value of the wave. This must be under 30.
Depth gives the amount the volume is cut into by the sine
wave, ranging 0.0 to 1.0 and defaulting to 0.5.
vol gain [ type [ limitergain ] ]
The vol effect is much like the command line option -v. It
allows you to adjust the volume of an input file and allows
you to specify the adjustment in relation to amplitude,
power, or dB. If type is not specified then it defaults to
amplitude.
When type is amplitude then a linear change of the amplitude
is performed based on the gain. Therefore, a value of 1.0
will keep the volume the same, 0.0 to < 1.0 will cause the
volume to decrease and values of > 1.0 will cause the volume
to increase. Beware of clipping audio data when the gain is
greater then 1.0. A negative value performs the same adjust-
ment while also changing the phase.
When type is power then a value of 1.0 also means no change
in volume.
When type is dB the amplitude is changed logarithmically.
0.0 is constant while +6 doubles the amplitude.
An optional limitergain value can be specified and should be
a value much less then 1.0 (ie 0.05 or 0.02) and is used only
on peaks to prevent clipping. Not specifying this parameter
will cause no limiter to be used. In verbose mode, this
effect will display the percentage of audio data that needed
to be limited.
BUGS
Please report any bugs found in this version of SoX mailing list (sox-
users@lists.sourceforge.net)
SEE ALSO
play(1), rec(1), soxexam(1)
The SoX web page at http://sox.sourceforge.net/
LICENSE
Copyright 2006 by Chris Bagwell
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.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MER-
CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
Public License for more details.
AUTHORS
Chris Bagwell (cbagwell@users.sourceforge.net).
Additional Authors and contributors are listed in the Changelog file
that is distributed with the source code.
sox December 11, 2001 SoX(1)