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siggen(1) Linux System Manual siggen(1)

NAME

siggen - an Ncurses based signal generator program

SYNOPSIS

DESCRIPTION

siggen is a simple signal generator program, with an Ncurses based user interface, that can digitally generate standard waveforms on the LINUX /dev/dsp device. 8 or 16 bit samples can be generated depending on the hardware.

siggen allows two independent waveforms to be generated. In stereo the two signals appear on different channels. In mono the two signals are digitally mixed onto the one mono channel.

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) are accurately meaningful. Higher frequencies can be specified, but don't expect to hear them!

On screen values for individual fields can be locked to prevent accidental changes. The unlock facility unlocks all locked fields.

Corresponding values for the 2 channels can be set to track, the values are made equal and a change to one causes a change to the other. e.g. making the frequency values track will make both channels the same frequency, and altering one freq. value alters both simultaneously.

The waveforms that can be generated are:

A standard sine wave
a sine wave with a 90 degree phase shift
a standard square wave with a 50% mark space ratio
a linear rise from 0 to peak, thru' 0 to negative peak, and back to 0
a ramp waveform with 'infinitely' fast flyback (:-) An ideal oscilloscope timebase signal.
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.
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).

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 leave the gain setting at 100(%). 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, by specifying a gain of > 100%. In fact a trapezoid signal can be made by generating a clipped sawtooth wave. The greater the gain, the closer the signal approaches a square wave (the rise and fall times decrease).

siggen ordinarily generates one seconds worth of 1 Hz samples at the specified samplerate, for each waveform, and generates frequency F by circularly sampling every Fth sample. Each buffer fragment is generated for the parameter(s) set at that moment. Buffer fragment sizes are set so that aprox. 10 fragments/sec are generated. Changing a generation parameter, e.g. waveform, frequency, gain, will impact the next buffer fragment generated, and hence changes appear to be almost immediate.

The -res option can be used to make siggen generate signals with 0.1Hz resolution, or 0.01Hz resolution. However be warned at 0.1Hz resolution the basic waveform sample buffers generated are each 10 times (and at 0.01Hz resolution 100 times) as big as the samplerate. It typically requires 5.5Mbytes of memory to run at 0.1Hz resolution, 16bit 32000 samples/sec. and 55Mbytes of memory to run at 0.01Hz resolution. Because of the large buffer sizes, the initial waveform calculation time can also be lengthy. Remember also that the waveforms are re-calculated whenever the playing parameters, 8/16bit, mono/stereo, samplerate are changed.

If your sounds periodically 'breaks' up with clicks or breaks, it is usually a sign that siggen is not being scheduled sufficiently often. Either increase the priority (see nice et al.), kill off other processes, get a faster processor, or increase the number of audio buffer fragments that siggen uses. This last will make siggen respond more sluggishly to changes in generation parameters. syslogd and crond are two processes that I've found useful to kill off - YMMV.

output to /dev/dsp, 22050 samples/sec, stereo if stereo card else mono, 16 bit samples if possible, else 8 bit, 3 audio buffer fragments.

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.
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.

siggen looks for configuration values BUFFERSPERSEC, CHANNELS, DACFILE, FRAGMENTS, RESOLUTION, SAMPLERATE, SAMPLESIZE, VERBOSE, VI_KEYS.

The aprox. number of sound buffer fragments to play every second (Sound buffersize is always a power of 2).
sets the number of channels, see '-c' option.
allows the name of the DAC/DSP/PCM device to be changed from /dev/dsp
The number of Audio Buffers to configure in the driver.
The minimum change possible to the frequency setting. Only 3 values allowed: 1Hz , 0.1Hz or 0.01Hz
sets the number of samples/sec for the DAC device
sets whether 8 or 16 bit samples to be generated
sets whether or not to run in verbose mode.
if set then the VI cursor moving keys "HJKL" are enabled

OPTIONS

display usage and help info
configure to play aprox. n audio buffers per second.
Use configfile as the LOCAL configuration file.
set number of audio buffers to n
be verbose
generate with samplerate of samples/sec
-8|-16 or -b 8|16
force 8 bit or 16 bit mode.
-1|-2
mono or stereo
set resolution of frequency generation. Valid values are: 1Hz, 0.l1Hz or 0.01Hz

EXAMPLES

FILES

SEE ALSO

signalgen, swgen, tones, sweepgen, siggen.conf

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

20 Aug 1999 Release 2