.TH signalgen 1 "20 Feb 1998" "Release 2.3" "Linux System Manual"
.I signalgen \- a simple signal generator program
.IP signalgen\ [flags]\ waveform\ freq
waveform is sine, cosine, square, triangle, sawtooth, noise
.IP signalgen\ [flags]\ pulse\ freq\ [Mark/Space]
pulse has extra param Mark/Space % - def. is 10 (%)
is a simple signal generator program, that can digitally generate standard
waveforms on the LINUX /dev/dsp device. 8 or 16 bit samples can be generated,
in mono or stereo. In stereo the two signals can be in phase or in anti-phase
(180 degrees). The frequency is specified as an integer number of Hertz.
Fractional Hertz frequencies are not supported. Of course, only frequencies
less than half the samplerate (number of samples/sec) can be generated.
The waveforms that can be generated are:
A standard sine wave
a sine wave with a 90 degree phase shift
a standard square wave with a 50% mark space ratio
a ramp waveform with 'infinately' fast flyback (:-) An ideal oscilloscope
shaped like equally spaced teeth on a saw (:-)
This is weak. All it consists of is one second of pseudo-randomly generated
samples, played repeatedly. I'd love to do proper white/pink noise,
but I don't know enough, and I don't think the structure of the program
is conducive to accurate noise generation.
A square waveform where the mark/space ratio (as a percentage) can be
specified. The default value is 10% (mark/space ratio of 1:9).
creates one second's worth of generated output in a buffer and plays the
buffer repeatedly, until it is terminated.
A lot of thought has gone into the algorithms for generating the waveforms.
I believe the sin/cos wave to be very pure (modulo your sound card :-), but
I don't have access to a THD meter to measure it. For best signal accuracy
use the gain factor option (\-A). The generator will then make the wave's
peak value fit the maximum digital values allowed. Use a mixer program to
control the output volume, or an external attenuator.
The gain factor option can be useful for simulating a signal that has been
subject to clipping. Specify a gain of > 100%. In fact a trapezoid signal
can be made by generating a clipped triangular wave. The greater the gain,
the closer the signal approaches a square wave (the rise and fall times
output to /dev/dsp, 22050 samples/sec, mono, 16 bit
samples if possible, else 8 bit.
display usage and help info
.IP -o\ file
write digital sample to file ('-' is stdout)
.IP -w\ file
as '\-o' but written as a WAVE format file. \-a (append) is not valid
with this option.
force overwrite/append of/to file.
.IP -C\ file
use "file" as the local configuration file (see below).
.IP -s\ samples
generate with samplerate of samples/sec
.IP -8/-16\ or\ -b\ 8|16
force 8 bit or 16 bit mode.
mono (def), stereo or stereo in antiphase
.IP -A\ n
scale samples by n/100, def. n is 100 (i.e. percentage of full scale output)
.IP -t\ N|Nm
generate output for either N secs or Nm millisecs only.
.IP -x10\ or\ -x100
Scale frequencies down by a factor of 10 or 100. This allows fractional
Hz values to be generated. See EXAMPLES below for its use. It is
.IP signalgen\ -v\ sin\ 440
generate a sin wave of 440Hz at 22050 samples/sec, 16bit samples on 16 bit
card, 8 bit samples on an 8 bit card.
.IP signalgen\ -v\ -s\ 44100\ -w\ sin444.wav\ sin\ 440
as above but at a samplerate or 44100/sec and save a one second of samples
as a WAVE file in sin440.wav
.IP signalgen\ -v\ -A\ 500\ saw\ 1000
generate a 1000Hz sawtooth wave severely clipped. The waveform will look like
a square wave with a rise and fall time of one tenth of the wave period. (I
think that's what the scribbled calculation on the back of this envelope
.IP signalgen\ -v\ -2a\ sin\ 1000
generate 2 1000Hz sine waves out of phase by 180 degrees, one on each
.IP signalgen\ -v\ pulse\ 1000\ 95
generate a 1000Hz pulse wave with the 'on' period being 95% of the
waveform period, i.e. a mark/space ratio of 19:1.
.IP signalgen\ -v\ -x10\ sin\ 2616
generate middle C 261.6Hz (2616/10) from the equally tempered scale. Yes
it's a royal pain remembering to scale all freqs. by a factor of 10, but
I needed it in a hurry and didn't have time to do it better.
.SH CONFIGURATION\ FILES
Three possible configuration files can be used: a LOCAL config file (usually
in current directory), a HOME config file in user's $HOME directory and a
GLOBAL config file.
All the siggen suite of programs are compiled with the names of the config
files built in. By default the configuration files are:
is the LOCAL config file.
is the HOME config file.
is the GLOBAL config file.
.IP signalgen\ -h
will indicate which config files will be searched for.
The config files do not have to exist. If they exist and are readable by the
program they are used, otherwise they are simply ignored.
The config files are always searched for configuration values in the order
LOCAL, HOME, GLOBAL. This allows a scheme where the sysadmin sets up default
config values in the GLOBAL config file, but allows a user to set some or
all different values in their own HOME config file, and to set yet more
specific values when run from a particular directory.
If no configuration files exist, the program provides builtin
default values, and most of these values can be set
by appropriate command line switches and flags.
See siggen.conf(5) for details of the configuration files.
looks for configuration values CHANNELS, DACFILE, SAMPLERATE,
sets either mono or stereo mode like the '\-1|\-2' options.
allows the name of the DAC/DSP/PCM device to be changed from /dev/dsp
sets the number of samples/sec for the DAC device
sets whether 8 or 16 bit samples to be generated
sets whether or not to run in verbose mode.
.SH SEE ALSO
.I Copyright\ 1995-2008\ Jim\ Jackson
The software described by this manual is covered by the GNU General
Public License, Version 2, June 1991, issued by :
Free Software Foundation, Inc.,
675 Mass Ave,
Cambridge, MA 02139, USA
Permission is granted to make and distribute verbatim copies of
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Permission is granted to copy and distribute modified versions of this
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Permission is granted to copy and distribute translations of this
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translation instead of in the original English.
.I Jim Jackson
.I Email: firstname.lastname@example.org