Twenty-ninth edition of the N&O column / Spooks newsletter

(Date: Fri, 01 Sep 2000 23:08:10 +0200)

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XPH decoder « XPERTA »

Valeriano Martin wrote a very nice DOS program with which you can translate the polytones to readable text. The first versions of the program, called « XPerta », did not run on various DOS and Windows machines, but the present version 2.01, seems to run smoothly on all pc's. All versions worked perfectly well on my pc's.

We elaborated on the decoding procedures in two articles that you can find in N&O #10 and #18. The tone codes mentioned in these articles differ slightly from the ones that XPerta uses. So, if you want to experiment yourself, use the following tone codes instead of the ones mentioned earlier.

XPerta works offline and uses an 8 or 16 bits PCM waveform (.wav) file as input. It can handle batches, so you decode can more files in one run. XPerta generates an ASCII text file with the results (see below).

The program needs some input before it starts decoding your files.

1. the name of the sound file or batch file.
2. the start position in seconds, where XPerta should start decoding.
3. the position in seconds where the decoding should stop.
4. threshold of acceptance: degree of distinctness that a tone should exceed to be perceived by the program. This value should be chosen according to reception quality. True tones may be ignored if this level is too high and, on the other hand, the noise may be masked as signs if this level is too low.
5. time step: interval between two serial measurements, expressed in milliseconds. A higher value increases the speed, but may decrease the accuracy.
6. output file: the name of the text file with the decoding results.

You can get your copy of XPerta from Valeriano's website.

There is also a link on the N&O site to XPerta and I uploaded a wav file of a complete XPH transmission in case you want to try Xperta but cannot find XPH.

Please let Valeriano know what you think about the program. His e-mail address: Valeriano Martin <tarabicu@worldonline.es>

Example of an output file:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
~                             XPERTA                                 ~ 
~                            ~~~~~~~~                                ~ 
~                          Version 2.01                              ~ 
~                                                                    ~ 
~            Valeriano Martin <tarabicu@worldonline.es>              ~ 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 

Sound file: xph.wav
Beginning: 0.000
End: 213.475
Thresold of acceptance: 0.15
Time step: 3.17


HEADER
343 343 343 1 343 343 343 1 343 343 343 1 343 343 343 1 
343 343 343 1 343 343 343 1 343 343 343 1 343 343 343 1 
343 343 343 1 

MESSAGE
>>>>>>>>>>>>>>>>>>>> _________01437 00095 27777 39755 37370 
00937 28393 55069 01410 93757 41417 72478 99956 65237 23597 
79272 70799 31987 39383 03288 32959 42466 88375 10278 62524 
05963 30513 96721 36094 86748 16957 99231 91641 89864 37132 
03772 61827 01506 68637 81623 50063 14681 30535 07714 58223 
14627 13364 72297 43475 63020 21898 36232 82418 81211 59939 
28612 42224 04948 07579 21895 45840 58678 30807 80592 52769 
16210 27084 35603 14149 48029 03249 72268 44338 52630 98513 
64462 02183 46315 40836 22696 76273 11030 56070 67471 71672 
51818 06607 38442 24582 45497 97593 31978 41790 01271 91253 
24127 25142<<<<<<<<<<<<<<<<<<<<

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