swgen(1)							Linux System Manual							  swgen(1)

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 max-
       imum  (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 chan-
       nel 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 genera-
       tor 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 trape-
       zoid 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.

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

Release 2.3							    20 Feb 1998 							  swgen(1)