sgen(1)                       Linux System Manual                      sgen(1)



NAME
       sgen - a simple signal generator program

SYNOPSIS
       sgen [flags] waveform freq
              waveform is sine, cosine, square, triangle, sawtooth, noise

       sgen [flags] pulse freq [Mark/Space]
              pulse has extra param Mark/Space % - def. is 10 (%)

DESCRIPTION
       sgen  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 sup
       ported. Of course, only frequencies less than half the samplerate (num
       ber 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-ran
              domly  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).

       sgen 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 wave
       forms.  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 exter
       nal 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
       sgen -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.

       sgen -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

       sgen -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 :-)

       sgen -v -2a sin 1000
              generate 2 1000Hz sine waves out of phase by 180 degrees, one on
              each stereo channel.

       sgen -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.

       sgen -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.

       sgen -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.

       sgen looks for configuration values CHANNELS, DACFILE, SAMPLERATE, SAM
       PLESIZE, 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 per
       mission notice identical to this one.

       Permission is granted to copy and distribute translations of this  man
       ual into another language, under the above conditions for modified ver
       sions, except that this permission notice may be included  in  transla
       tion instead of in the original English.

AUTHOR
       Jim Jackson

       Email: jj@franjam.org.uk



Release 2.3                       20 Feb 1998                          sgen(1)
