make
./grothe carrier_freq pixelclock horizontal_total < some_input.txt
Put on your “electronic ears” and then try:
./try.sh
You may find using a tunable scanning electronic ear helps.
Most of the time, interference is annoying. This entry is the exception that proves the rule. What is a bug to some is a feature to this entry. :-)
The program draws patterns on the screen that can be picked up by a
shortwave radio. It emulates
the frequencies for an old fashion touch tone phone, so old songs can be played
by hitting 0-9
,#
, and *
.
To be able to run the program you need to determine the following parameters:
carrier_freq - base frequency used to host music
pixelclock - refresh rate of the monitor
horizontal_total - total scan along the horizontal axis
If you have xvidtune
installed you can get the pixelclock
and
horizontal_total
with the following command
xvidtune -show | head -n 1 | awk '{ print "pixelclock " $2 * 1000000 " horizontal_total = " $6 }'
Example from my laptops:
./grothe 65000000 10000000 1344 < twinkle.txt
Even if the user gets a setting off, the sound will usually be able to be heard on AM at a multiple of the original frequency.
The core idea of using a machine to play music on AM radio goes all the way back to the Altair computers and Timex Sinclair ZX-81s.
Olympics Fanfare - from antang@phakt.usc.edu
- Tony:
4-9-91231,2222-321123123-9-91231,2222-32112321
Twinkle Twinkle Little Star - from fsufunkyb@aol.com
- Ben Schmidt:
1199##9-6633221-9966332-9966332-1199#9-6633221-
Generic Arabian Tune - from rdippold@qualcomm.com
- Ron “Asbestos” Dippold:
453,54,4569564459,9#95458,8987453 54
Others can be found by doing a search for “touch tone phone songs”.
Some numbers expressed in Octal, some in hex and some in decimal: “A foolish consistency is the hobgoblin of little minds” - Ralph Waldo Emerson.
Funky scoping, looking at the nanosleep section and XsetWindowAttributes
declares local variables.
Algorithm is very weird, uses y
dimension to draw carrier frequency
and x
dimension to draw audio frequency, based on Erik
Thiele’s
Tempest for Eliza.
lack of #define
s confuses many people :-)
figuring out your pixelclock
and horizontal_total
and which carrier_freq
to use can be an exercise in obfuscation for the user.
use of commas in various places, confuses most C code beautifiers sometimes making the beautified code harder to read
use of static
to ensure initialization is EVIL and done in several
places
uses static
declarations & void
function returns we don’t care about
making the code harder to read.
does sound using only X11 libs, no other libs required.
demonstrates tempest emissions in a fun/easy way.
follows good programming practices of actually setting exit codes and giving usage when run with incorrect parameters.
Tempest for Eliza - Basis for Algorithms.
Tempest
AM
- Another early program in this field. See
here
for a bit more information on the program (search for Tempest-AM Radio Signal Transmitter
).
The paper Soft Tempest: Hidden Data Transmission Using Electromagnetic Emanations by Markus G. Kuhn’s and Ross J. Anderson’s.