signalgen - Online in the Cloud

PROGRAM:

NAME

signalgen - a simple signal generator program

SYNOPSIS

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

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

DESCRIPTION

signalgen 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 supported. Of course, only frequencies less than half the samplerate (number 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-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).

signalgen 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 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 NEVER use the gain factor option (-A). 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. 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

signalgen -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.

signalgen -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

signalgen -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 :-)

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

signalgen -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.

signalgen -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.

signalgen -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.

signalgen looks for configuration values CHANNELS, DACFILE, SAMPLERATE, SAMPLESIZE,
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.

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