- sweepgen [options]
DESCRIPTIONsweepgen 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:
- A standard sine wave
- 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) 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.
- output to /dev/dsp, 22050 samples/sec, stereo if stereo card else mono, 16 bit samples if possible, else 8 bit.
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:
- is the LOCAL config file.
- is the HOME config file.
- 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.
- The aprox. number of sound buffer fragments to play every second (Sound buffersize is always a power of 2).
- sets the number of channels, mono or stereo.
- 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
- display usage and help info
- be verbose
- -s samples
- generate with samplerate of samples/sec
- -8|-16 or -b 8|16
- force 8 bit or 16 bit mode.
- mono or stereo mode
- -res n
- set resolution of frequency generation. Valid values are: 1Hz, 0.l1Hz or 0.01Hz
COPYINGCopyright 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.
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