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SUMMARY:
xfreq is a spectrum analyzer program by Philip VanBaren. If you have
X11 this file will show you how to run both xoscope and xfreq together
to see signals in the time and frequency domains simultaneously in two
windows. Of course doing this will slow things down since Linux will
need to split processing time across the two processes. But it works
quite well for repetitive signals.
WHAT YOU NEED:
* The "freq51" distribution from sunsite.unc.edu or a mirror.
ftp://sunsite.unc.edu/pub/Linux/apps/sound/freqs/
* "libsrgp" from the "srgp" distribution, also available at sunsite.
ftp://sunsite.unc.edu/pub/Linux/libs/X/
INSTALLATION:
Patch xfreq so that it can run as an external "ofreq" math command
from xoscope:
* tar zxvf freq51.tar.gz
* cd freq51/source
* patch < /path/to/oscope/source/patch.f51
* edit the "DEFINES" line of makefile.srgp_linux if you put your
ofreq.ini file somewhere other than /usr/local/lib/oscope/ofreq.ini
* make -f makefile.srgp_linux clean
* make -f makefile.srgp_linux dep
* make -f makefile.srgp_linux all
* cp -p xfreq /usr/local/bin (or wherever you want xfreq)
* ln -s /usr/local/bin/xfreq /usr/local/lib/oscope/ofreq
(fix the paths if necessary)
USAGE:
You should now have a modified xfreq that has an option to use xoscope
as a "soundcard input device". Run `xfreq -h` to see the complete
usage. This new "ofreq" command can now be launched from xoscope as
an external math command.
By default, xfreq looks for a "freq.ini" file in the current directory
for initial configuration. When the new xfreq is launched with the
name "ofreq", it will instead look for the ini file in the path
specified in the makefile (/usr/local/lib/oscope/ofreq.ini). This is
so the needed parameters can be set correctly independent of where you
happen to be running xoscope. I have included an ofreq.ini file that
sets the minimum parameters you will need to use when running ofreq
from xoscope. These are (with command-line equivalents):
Soundcard: 2 (-C2)
To use xoscope (stdin/stdout pipe) as the "soundcard" input
Sample rate: 44000 (-S44000)
Most likely sample rate. You must use the same rate in both xoscope
and xfreq or the results will be wrong.
FFT length: 512 (-F512)
The FFT length must be a power of 2 and less than xoscope's sample
depth (screen width). Since xoscope's width is 640 by default,
512 is the best number to use. If you use 1024 (the default), the
programs will hang as they wait for samples from each other.
Background color: 0,0,0
To give xfreq a black background like xoscope.
* Now start xoscope.
* Select channel 3 or above and make it visible.
* Hit '$' or click on "Extern..."
* enter "ofreq" in the dialog.
This should launch ofreq in a separate window, displaying the FFT of
channel 1. Now all the normal keys should work; hit 'h' to display
what the keys are. Use '[' to switch the input channel, 'x' and 'y'
to change the axis scales, etc. You will need to hit 'r' and correct
the sampling rate if you change the sampling rate in xoscope.
That's it!
Tim Witham <twitham@pcocd2.intel.com>
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