NAME
sweepgen - an Ncurses based sweep generator program
SYNOPSIS
sweepgen [options]
DESCRIPTION
sweepgen is a simple sweep signal generator program, with an Ncurses
based user interface, that can digitally generate waveforms on the
LINUX /dev/dsp device. 8 or 16 bit samples can be generated depending
on the hardware.
sweepgen in MONO mode outputs the generated swept waveform. In STEREO
mode the swept waveform is output on one channel, and the sweeping
waveform is output on the second channel.
The sweeping frequency is by default specified as an integer number of
Hertz. Fractional Hertz frequencies, specifiable to 0.1Hz or 0.01Hz
resolution, are supported by use of the -res command line option, or
the resolution parameter in the configuration file(s). 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.
The swept waveform frequencies are specified either as a lower and
upper frequency, or as a centre frequency with a frequency variation.
1000 500
would signify a range of 1000-500 Hz to 1000+500 Hz, i.e. 500 to
1500 Hz
Of course, only frequencies less than half the samplerate (number of
samples/sec) can be generated. Although this is not checked.
The waveforms that can be used as either the sweeping or swept signals
are:
sine A standard sine wave
square a standard square wave with a 50% mark space ratio
triangle
a linear rise from 0 to peak, thru’ 0 to negative peak, and back
to 0
sawtooth
a ramp waveform with ’infinitely’ fast flyback (:-) An ideal
oscilloscope timebase signal.
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)
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.
At 1Hz resolution, sweepgen generates one seconds worth of 1 Hz samples
at the specified samplerate, for each waveform, and generates sweeping
frequency F by circularly sampling every Fth sample. These samples are
scaled to fit the swept frequency range and are used to sample the
swept waveform to generate the swept signal. Each buffer fragment is
generated for the parameter(s) set at that moment. By default, buffer
fragment sizes are set so that aprox. 10 fragments/sec are generated.
Changing a generation parameter, e.g. waveform, frequency, 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.
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.
siggen -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.
sweepgen looks for configuration values BUFFERSPERSEC, CHANNELS,
DACFILE, FRAGMENTS, RESOLUTION, SAMPLERATE, SAMPLESIZE, VERBOSE,
VI_KEYS.
BUFFERSPERSEC
The aprox. number of sound buffer fragments to play every second
(Sound buffersize is always a power of 2).
CHANNELS
sets the number of channels, mono or stereo.
DACFILE
allows the name of the DAC/DSP/PCM device to be changed from
/dev/dsp
FRAGMENTS
The number of Audio Buffers to configure in the driver.
RESOLUTION
The minimum change possible to the frequency setting. Only 3
values allowed: 1Hz , 0.1Hz or 0.01Hz
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.
VI_KEYS
if set then the VI cursor moving keys "HJKL" are enabled
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 mode
-res n set resolution of frequency generation. Valid values are: 1Hz,
0.l1Hz or 0.01Hz
EXAMPLES
FILES
SEE ALSO
swgen, signalgen, siggen, tones
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