Hi Bill,

I’m kind of stuck at the moment. Hoping that you will see something that I’m 
missing. In r6773, I am getting consistent decoding results using either 
msk144d or wsjt-x on linux, but on OS X I am getting different results between 
msk144d and wsjt-x, and also different results between either of these programs 
on OS X and linux.

If you get a chance, perhaps you can run on Windows and see what happens. Maybe 
we’ll find that the problem is specific to OS X? Dunno. In any case, here’s a 
link to a zipped batch of wav files. These are recordings of Joe sending MSK144:

https://dl.dropboxusercontent.com/u/33211132/msk144_test2_0604_k9an.zip

For the record, here’s what I get when I decode these files on linux using the 
following command (from within the wsjtx/build directory:

$ ./msk144d ~/Desktop/msk_test\ data/msk144_test2_0604_k9an/*.wav
115345   1  4.7 1497 & K9AN K1JT FN20                                          
115445   0  2.8 1492 & K9AN K1JT FN20                                          
115515   0  6.5 1491 & K9AN K1JT FN20                                          
115615   0  0.8 1493 & K9AN K1JT FN20                                          
115715   0 10.4 1493 & K9AN K1JT FN20                                          
115915   0  2.0 1492 & K9AN K1JT FN20                                          
120045   0 14.0 1491 & K9AN K1JT FN20                                          
120115  -3  1.5 1495 & K9AN K1JT FN20                                          
120245   4 10.3 1491 & K9AN K1JT FN20                                          
120315   0  2.1 1492 & K9AN K1JT FN20                                          
120345   3  9.2 1491 & K9AN K1JT FN20                                          
120415   2  2.6 1499 & K9AN K1JT FN20                                          
120945   1 12.7 1497 & K9AN K1JT FN20                                          
121045   1  2.4 1486 & K9AN K1JT FN20                                          
121115  -1 11.6 1493 & K9AN K1JT FN20                                          
121145   7  2.9 1491 & K9AN K1JT FN20                                          
121345   0  5.8 1495 & K9AN K1JT FN20                                          
121445   1  0.4 1497 & K9AN K1JT FN20                                          
121515   4 12.4 1496 & K9AN K1JT FN20                                          
121715   1 12.2 1488 & K9AN K1JT FN20                                          
121815   2 10.7 1494 & K9AN K1JT FN20                                          
121845   6  8.1 1492 & K9AN K1JT FN20

I get the same results if I decode from wsjt-x on linux. The results from 
running msk144d on OS X are almost the same, but there are a couple of 
differences. But if I run from within wsjt-x on OS X, I get the following:

115515   0  6.5 1491 & K9AN K1JT FN20
115615   0  5.9 1492 & K9AN K1JT FN20
115715   0 10.4 1493 & K9AN K1JT FN20
115915   0  2.0 1492 & K9AN K1JT FN20
120045   1 14.0 1493 & K9AN K1JT FN20
120245   4 10.3 1490 & K9AN K1JT FN20
120345   3  9.2 1490 & K9AN K1JT FN20
120415   2  2.7 1499 & K9AN K1JT FN20
120945   1 12.7 1496 & K9AN K1JT FN20
120945  -1 13.3 1492 & 9BVTCXFI4N5R
121115  -1 11.6 1492 & K9AN K1JT FN20
121145   7  2.9 1490 & K9AN K1JT FN20
121345   1  5.8 1496 & K9AN K1JT FN20
121515   4 12.4 1495 & K9AN K1JT FN20
121715   1 12.2 1488 & K9AN K1JT FN20
121815   2 10.7 1493 & K9AN K1JT FN20
121845   6  8.1 1492 & K9AN K1JT FN20

Instead of 22 decodes, I’m getting only 17 decodes, and one of them is a false 
decode. And some of the files that did decode on both platforms provide 
different results, i.e. different candidates decoded successfully, as can be 
seen for example in the different time stamps for the 115615 results given 
above. This suggests that there is some data corruption somewhere.

A while back, Joe added “srand(-1)” to the ldpc_decode routine located in 
/lib/ldpc/dec.c to ensure that the random number generator that is used to 
dither the soft-symbols would be initialized the same way across runs and 
platforms. This is the only “randomization” that this algorithm is doing - 
everything else should be deterministic. Comments/suggestions would be most 
welcome!

Steve k9an




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