Re: LF: SlowJT9 averaging (in conversion to JT9-1)

[Rik Strobbe <rik.strobbe@kuleuven.be>]

​Hello Andy,

no I am not sure it is THE best way, it is just MY best way.

Adapting the WSJT-X JT9 decoder might be a better option.

Creating a nice interface is within my range but I am not sure I am capable of changing the WSJT-X JT9 decoder (agree, there is only one way to find out about that ...).

Basicaly I was looking for a fast way to get JT9-2 and eventually JT9-5 and JT9-10 rolling again, as I am convinced that these modes (certainly JT9-2) can contribute to more long distance QSO's (I plead guilty to be one of these old school hams that still want to make QSO's, the further the better).

And as far as I understand, in theory "speeding up" (with averaging) to JT9-1 should get the same result as adapting the decoder software.

 

But suggestions to do it another (preferable better) way are welcome. 

And if someone feels the itch to adapt the JT9 decoder (or write an own decoder) I will be happy to implement that in SlowJT9.

73, Rik  ON7YD - OR7T

---

Van: owner-rsgb_lf_group@blacksheep.org <owner-rsgb_lf_group@blacksheep.org> namens Andy Talbot <andy.g4jnt@gmail.com>
Verzonden: woensdag 21 november 2018 17:11
Aan: rsgb_lf_group@blacksheep.org
CC: 600MRG@mailman.qth.net; rsgb_lf_group
Onderwerp: Re: LF: SlowJT9 averaging (in conversion to JT9-1)

 

Rik

Are you sure you are going about this the best way?   If you want to stay with the original JT9-slow values, then wouldn't it be better to go to the WSJT repository and find the original source code.   Or dive inside the decoding software and change the numbers, instead of speeding things up and averaging

ALTERNATIVELY, if you wish to stay with the speeded up version and the latest decoder, then go back to your original idea of integer ratios.   Forget backwards compatibility.  After all, no one is likely to be using the old WSJT-X 1 suite with these modes so there is no need for backwards compatibility.   You can start with a fresh and the simpler approach

The only thing I suggest is that you change the name of the mode slightly.   Stay with JT9 for the normal one, but instead of JT9-2 and JT9-5 call it , say JT9-R2 and JT9-R4   (R for Rik :-)  That way no one can think it is backwards compatible.

Andy

www.g4jnt.com

On Wed, 21 Nov 2018 at 15:53, Rik Strobbe <rik.strobbe@kuleuven.be> wrote:

For those interested:

in order to get JT9-2, JT9-5 and JT9-10 signals decoded with a JT9 decoder (from the WSJT-X suite), the JT9-2, JT9-5, JT9-10 audio is "speeded up" to JT9-1. During the process the signal is also averaged (otherwise ther would be no S/N improvement).

In the initial versions of SlowJT9 the ratios were integer values: 2 for JT9-2 anf 5 for JT9-5, making averaging very simple.

In SlowJT9 v0.9.10 however the original parameters for JT9-2, JT9-5 and JT9-10 are used, resulting in some non-integer conversion rates: 2.2222 (15360/6912) for JT9-2 and 5.9259 (40960/6912) for JT9-5.

So, how to average with for example each 2.2222 incoming samples are converted to 1 outgoing sample?

Not finding relevant information about this on the web, I did it quite straigh forward:

Assuming I1, I2, I3, I4, ... are the incoming JT9-2 samples and O1, O2, O3, O4, ... are the outgoing JT9(-1) samples

O1 = (I1+I2+0.222*I3)/2.222

O2 = (0.778*I3+I4+0.444*I5)/2.222

O3 = (0.556*I5+I6+0.667*I7)/2.222

O4 = (0.333*I7+I8+0.889*I9)/2.222

and so on.

I am by no means sure that this is the best way to average for non-integer conversion rates (it was just the best I could think of), so any suggestion to do this better is welcome.

73, Rik  ON7YD - OR7T