Ubuntu Manpage: swgen - a simple swept frequency signal generator

NAME

       swgen - a simple swept frequency signal generator

SYNOPSIS

       swgen [-2] [-s samples] [-8/-16|-b 8/16] [sweepwaveform]
              sweepfreq [sweptwaveform] minfreq maxfreq

       swgen [-2] [-s samples] [-8/-16|-b 8/16] [sweepwaveform]
              sweepfreq [sweptwaveform] centrefreq percent%

       waveform, either sweep or swept,
              is sine, cosine, square, triangle, sawtooth, noise

       for full list of options see below.

DESCRIPTION

swgen generates a swept frequency waveform on the LINUX /dev/dsp device. The swept and sweep waveform can
be separately specified, as can the sweep frequency range and the sweeping frequency. Sweep frequency
range can be specified either by giving the minimum (start) and maximum (end) frequency in Hertz; or by
giving the centre frequency and the percentage frequency variation below and above. The percentage is
given as an integer value from 0 to 100.

The default sweep waveform is a sawtooth (ramp), and the default swept waveform is a sine. If the
soundcard can do 16 bit samples, swgen will do 16 bit by default.

8 or 16 bit samples can be generated, in mono or stereo. In stereo, one channel carries the swept
frequency signal, while the second channel carries the sweeping signal. This can be useful fed to the X
input of an oscilloscope when displaying frequency response curves etc.

The samples can be written in raw or WAV format to files instead of to the sound device.

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 'infinitely' 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.

swgen 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

       -f,-a  force overwrite/append of/to file.

       -C file
              use "file" as the local configuration file (see below).

       -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.

       -s samples
              generate with samplerate of samples/sec

       -8/-16 or -b 8|16
              force 8 bit or 16 bit mode.

       -1,-2  mono (def), or special stereo mode (see above).

       -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

       swgen -v 2 100 1000
              sweep a sin wave from 100Hz to 1000Hz using a sawtooth wave twice a second, at 22050  samples/sec,
              16bit samples on 16 bit card, 8 bit samples on an 8 bit card.

       swgen -v -s 44100 -w sweep.wav 2 100 1000
              as  above  but  at  a  samplerate  or  44100/sec  and save one second of samples as a WAVE file in
              sweep.wav

       swgen -v -2 squ 10 1000 20%
              generate a sine wave switched by a 10Hz squarewave between 800Hz and 1200Hz.  The swept signal  is
              on one channel and the 10Hz square wave is on the second channel.

       swgen -v -x10 5 4400 4500
              generate  a swept sine wave from 440Hz (4400/10) to 450Hz (4500/10), being swept at a frequency of
              0.5Hz (5/10). Yes it's a royal pain remembering to scale all freqs. up 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.

swgen -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.

swgen 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.

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