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