NAME
siggen - an Ncurses based signal generator program
SYNOPSIS
siggen [-s samplerate] [-8|-16|-b 8|-b 16] [-1|-2]
DESCRIPTION
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
hardware.
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
hear them!
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
triangle
a ramp waveform with ’infinitely’ fast flyback (:-) An ideal
oscilloscope timebase signal.
sawtooth
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
noise generation.
pulse 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).
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
external attenuator.
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.
Defaults
output to /dev/dsp, 22050 samples/sec, stereo if stereo card
else mono, 16 bit samples if possible, else 8 bit, 3 audio
buffer fragments.
OPTIONS
-h display usage and help info
-v be verbose
-s samples
generate with samplerate of samples/sec
-8|-16 or -b 8|16
force 8 bit or 16 bit mode.
-1|-2 mono or stereo
EXAMPLES
FILES
SEE ALSO
signalgen, swgen, tones, sweepgen
BUGS
COPYING
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 this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be included in
translation instead of in the original English.
AUTHOR
Jim Jackson
Email: jj@franjam.org.uk