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Re: [RTTY] RttyCompare

To: "VE3NEA" <alshovk@dxatlas.com>
Subject: Re: [RTTY] RttyCompare
From: Jerry Flanders <jeflanders@comcast.net>
Date: Tue, 01 Feb 2005 04:02:51 +0000
List-post: <mailto:rtty@contesting.com>
Hello Alex

Can you distribute the simulated audio files?

I have WSCGen, PathSym, and RttyCompare working fine. I can generate audio files and add the distortion effects to them with PathSim. Amazing how genuine the flutter effects sound!

I couldn't get Virtual Audio Cable 2.04 installed under XP Pro, so downloaded the current V3.something, which appears to work, but I have no confidence in it because I can hear a buzzing in the RTTY audio files when I route them through it. No buzzing otherwise. I was finally able to patch a file through it and into MMTTY and see copy (even with the buzz) , so I am encouraged that this is going to be a valid test procedure when I learn all the tricks and eliminate the buzz.

Since I have two sound cards in the computer my next step will be to try to avoid using VAC (and the buzzing) by just patching externally from one card to the other with a hardware cable. A guy with two computers could also just patch between them in the same way. (Guys with just one standard computer could probably play the files into an external audio recorder and then feed it back into the program under test via the sound card .)

In the process of learning how to use the various pieces, it occurred to me that if you just packaged and distributed the final path-simulated audio files, it would cut out much of the work and uncertainty for the test preparation process. It would also cut out many hours of the next guy trying to learn to use WSCGen, Pathsim, and VAC and possibly coming up with bad data due to a preparation error of some kind. Having standardized audio files ready to go should also help to standardize the tests.

Jerry W4UK

At 18:17 1/29/2005, you wrote:
I was wondering how the popular RTTY programs compare to each other in terms
of decoding accuracy. To my surprise, a search on the Internet proved that
such a comparison had never been performed, and I had no choice but running
a series of tests myself. I downloaded PathSim from the AE4JY web site and
generated a set of messages with AWGN, flat and selective fading, flutter,
and multi-path delay. Then I decoded these messages with MMTTY, MixW and
TrueTTY, and tried to count the errors.

It was immediately obvious why no one did such tests before. Counting errors
was a very time consuming task and, more importantly, was possible only at
low error rates. At CER = 10% or so it was virtually impossible to match the
two sequences of characters and tell the correct letters from the wrong
ones.

To solve this problem, I wrote an RTTY message comparison tool, RttyCompare.
The program converts the transmitted and received text to the Baudot code
and compares the two sequences using the standard dynamic programming
algorithm, counts the missing and incorrect codes, and instantly calculates
CER. It is robust enough at error rates as high as 50% and even higher.

Equipped with RttyCompare, I had no problems completing my tests. The
comparison results are available at http://www.dxatlas.com/rtty with a
description of the testing procedures. RttyCompare can be downloaded from
the same site, with source code.

I am far from drawing any conclusions from the tests, this is just a request
for a discussion. The procedures that I used must be verified by other hams,
and the results must be independently reproduced. Now that the testing
procedure is documented and a complete list of required tools is identified,
everyone can do a similar test - perhaps with longer messages, more
realistic PathSim profiles, and for a wider variety of RTTY programs
(cocoaModem ?).

73 Alex VE3NEA


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