siggen - an Ncurses based signal generator program
siggen [-s samplerate] [-8|-16|-b 8|-b 16] [-1|-2]
siggen is a simple signal generator program, with an Ncurses based user
interface, that can digitally generate standard waveforms on the LINUX
/dev/dsp device. 8 or 16 bit samples can be generated depending on the
siggen allows two independant waveforms to be generated. In stereo the
two signals appear on different channels. In mono the two signals are
digitally mixed onto the one mono channel.
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) are accurately
meaningful. Higher frequencies can be specified, but don’t expect to
The waveforms that can be generated are:
sine A standard sine wave
cosine a sine wave with a 90 degree phase shift
square a standard square wave with a 50% mark space ratio
a ramp waveform with ’infinitely’ fast flyback (:-) An ideal
oscilloscope timebase signal.
shaped like equally spaced teeth on a saw (:-)
noise 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
pulse A square waveform where the mark/space ratio (as a percentage)
can be specified. The default value is 10% (mark/space ratio of
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 leave the gain setting at 100(%). 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
The gain factor option can be useful for simulating a signal that has
been subject to clipping, by specifing a gain of > 100%. In fact a
trapezoid signal can be made by generating a clipped sawtooth wave. The
greater the gain, the closer the signal approaches a square wave (the
rise and fall times decrease).
siggen generates one seconds worth of 1 Hz samples at the specified
samplerate, for each waveform, and generates frequency F by circularly
sampling every Fth sample. Each buffer fragment is generated for the
parameter(s) set at that moment. Buffer fragment sizes are set so that
aprox. 10 fragments/sec are generated. Changing a generation parameter,
e.g. waveform, frequency, gain, will impact the next buffer fragment
generated, and hence changes appear to be almost immediate.
If your sounds periodically ’breaks’ up with clicks or breaks, it is
usually a sign that siggen is not being scheduled sufficiently often.
Either up the priority (see nice et al.), kill off other processes, get
a faster processor, or increase the number of audio buffer fragments
that siggen uses. This last will make siggen respond more sluggishly to
changes in generation parameters. syslogd and crond are two processes
that I’ve found useful to kill off - YMMV.
output to /dev/dsp, 22050 samples/sec, stereo if stereo card
else mono, 16 bit samples if possible, else 8 bit, 3 audio
-h display usage and help info
-v be verbose
generate with samplerate of samples/sec
-8|-16 or -b 8|16
force 8 bit or 16 bit mode.
-1|-2 mono or stereo
signalgen, swgen, tones, sweepgen
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
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