NAME
signalgen - a simple signal generator program
SYNOPSIS
signalgen [flags] waveform freq
waveform is sine, cosine, square, triangle, sawtooth, noise
signalgen [flags] pulse freq [Mark/Space]
pulse has extra param Mark/Space % - def. is 10 (%)
DESCRIPTION
signalgen 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:
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
sawtooth
a ramp waveform with ’infinately’ fast flyback (:-) An ideal
oscilloscope timebase signal.
triangle
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).
signalgen 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 NEVER 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 decrease).
Defaults
output to /dev/dsp, 22050 samples/sec, mono, 16 bit samples if
possible, else 8 bit.
OPTIONS
-h display usage and help info
-v be verbose
-o file
write digital sample to file (’-’ is stdout)
-w file
as ’-o’ but written as a WAVE format file. -a (append) is not
valid with this option.
-f,-a force overwrite/append of/to file.
-C file
use "file" as the local configuration file (see below).
-s samples
generate with samplerate of samples/sec
-8/-16 or -b 8|16
force 8 bit or 16 bit mode.
-1,-2,-2a
mono (def), stereo or stereo in antiphase
-A n scale samples by n/100, def. n is 100 (i.e. percentage of full
scale output)
-t N|Nm
generate output for either N secs or Nm millisecs only.
-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 a Kludge.
EXAMPLES
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.
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
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 gives :-)
signalgen -v -2a sin 1000
generate 2 1000Hz sine waves out of phase by 180 degrees, one on
each stereo channel.
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.
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.
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:
./.siggen.conf
is the LOCAL config file.
$HOME/.siggen.conf
is the HOME config file.
/etc/siggen.conf
is the GLOBAL config file.
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.
signalgen looks for configuration values CHANNELS, DACFILE, SAMPLERATE,
SAMPLESIZE, VERBOSE.
CHANNELS
sets either mono or stereo mode like the ’-1|-2’ options.
DACFILE
allows the name of the DAC/DSP/PCM device to be changed from
/dev/dsp
SAMPLERATE
sets the number of samples/sec for the DAC device
SAMPLESIZE
sets whether 8 or 16 bit samples to be generated
VERBOSE
sets whether or not to run in verbose mode.
SEE ALSO
siggen.conf(5)
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