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 independent 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 specifying 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