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

To: "[email protected]" <[email protected]>
Subject: Re: LF: SlowJT9 averaging (in conversion to JT9-1)
From: Andy Talbot <[email protected]>
Date: Wed, 21 Nov 2018 16:11:59 +0000
Cc: [email protected], rsgb_lf_group <[email protected]>
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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.

On Wed, 21 Nov 2018 at 15:53, Rik Strobbe <[email protected]> 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

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