SYNOPSIS

siggen [-s samplerate] [-8|-16|-b 8|-b 16] [-1|-2]

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!

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

triangle

a ramp waveform with 'infinitely' fast flyback (:-) An ideal oscilloscope timebase signal.

sawtooth

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.

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).

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 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.

If your sounds periodically 'breaks' up with clicks or breaks, it is usually a sign that siggen is not being scheduled sufficiently often. Either up 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.

Defaults

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.

OPTIONS

-h

display usage and help info

-v

be verbose

-s samples

generate with samplerate of samples/sec

-8|-16 or -b 8|16

force 8 bit or 16 bit mode.

-1|-2

mono or stereo

EXAMPLES

FILES

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: [email protected]