A detailed description of each synth parameter follows:
len is the length of audio to synthesise expressed as a time or
as a number of samples; 0=inputlength, default=0.
The format for specifying lengths in time is hh:mm:ss.frac. The
format for specifying sample counts is the number of samples
with the letter ‘s’ appended to it.
type is one of sine, square, triangle, sawtooth, trapezium, exp,
[white]noise, pinknoise, brownnoise; default=sine
combine is one of create, mix, amod (amplitude modulation), fmod
(frequency modulation); default=create
freq/freq2 are the frequencies at the beginning/end of synthesis
in Hz or, if preceded with ‘%’, semitones relative to A
(440 Hz); for both, default=%0. If freq2 is given, then len
must also have been given. Not used for noise.
off is the bias (DC-offset) of the signal in percent; default=0.
ph is the phase shift in percentage of 1 cycle; default=0. Not
used for noise.
p1 is the percentage of each cycle that is ‘on’ (square), or
‘rising’ (triangle, exp, trapezium); default=50 (square,
triangle, exp), default=10 (trapezium).
p2 (trapezium): the percentage through each cycle at which
‘falling’ begins; default=50. exp: the amplitude in percent;
p3 (trapezium): the percentage through each cycle at which
‘falling’ ends; default=60.
tempo [-q] factor [segment [search [overlap]]]
Change the audio tempo (but not its pitch) using a ‘WSOLA’ algo-
rithm. The audio is chopped up into segments which are then
shifted in the time domain and overlapped (cross-faded) at
points where their waveforms are most similar (as determined by
measurement of ‘least squares’).
By default, linear searches are used to find the best overlap-
ping points; if the optional -q parameter is given, tree
searches are used instead, giving a quicker, but possibly lower
factor gives the ratio of new tempo to the old tempo.
The optional segment parameter selects the algorithm’s segment
size in milliseconds. The default value is 82 and is typically
suited to making small changes to the tempo of music; for larger
changes (e.g. a factor of 2), 50 ms may give a better result.
When changing the tempo of speech, a segment size of around
30 ms often works well.
The optional search parameter gives the audio length in mil-
liseconds (default 14) over which the algorithm will search for
overlapping points. Larger values use more processing time and
do not necessarily produce better results.
The optional overlap parameter gives the segment overlap length
in milliseconds (default 12).
See also stretch for a similar effect.
treble gain [frequency [width[s|h|o|q]]]
Apply a treble tone-control effect. See the description of the
bass effect for details.
tremolo speed [depth]
Apply a tremolo (low frequency amplitude modulation) effect to
the audio. The tremolo frequency in Hz is given by speed, and
the depth as a percentage by depth (default 40).
Note: This effect is a special case of the synth effect.
trim start [length]
Trim can trim off unwanted audio from the beginning and end of
the audio. Audio is 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. 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 or
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 ½ seconds into the audio. 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.
vol gain [type [limitergain]]
Apply an amplification or an attenuation to the audio signal.
Unlike the -v option (which is used for balancing multiple input
files as they enter the SoX effects processing chain), vol is an
effect like any other so can be applied anywhere, and several
times if necessary, during the processing chain.
The amount to change the volume is given by gain which is inter-
preted, according to the given type, as follows: if type is
amplitude (or is omitted), then gain is an amplitude (i.e. volt-
age or linear) ratio, if power, then a power (i.e. wattage or
voltage-squared) ratio, and if dB, then a power change in dB.
When type is amplitude or power, a gain of 1 leaves the volume
unchanged, less than 1 decreases it, and greater than 1
increases it; a negative gain inverts the audio signal in addi-
tion to adjusting its volume.
When type is dB, a gain of 0 leaves the volume unchanged, less
than 0 decreases it, and greater than 0 increases it.
See  for a detailed discussion on electrical (and hence audio
signal) voltage and power ratios.
Beware of Clipping when the increasing the volume.
The gain and the type parameters can be concatenated if desired,
e.g. vol 10dB.
An optional limitergain value can be specified and should be a
value much less than 1 (e.g. 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 the audio that needed to be limited.
See also compand for a dynamic-range compression/expansion/lim-