Mooneer’s FreeDV Update – September 2024

This month was spent continuing the RADAE prototyping and testing efforts started last month. I focused primarily on creating a prototype of the FreeDV application that is able to route audio to/from separate processes that can actually handle the RADAE modulation and demodulation. By doing so, technically-inclined users can get an idea as to how RADAE would work with actual two way QSOs on the air.

One major challenge was getting transmit working reliably. With the prototype scripts, there was a few seconds delay on startup before a modulated signal could actually go out over the air. This was fixed by simply never stopping the TX or RX scripts. There’s still a delay at the beginning but for the current test effort, it’s tolerable.

Another challenge is that forking processes on Windows works significantly differently than on Unix/Linux (especially if you want to route stdin/stdout through your application). RADAE has a feature where on the end of transmission, a special signal is sent out that immediately causes squelch to close. This prevents the R2D2 sounding audio at the end of transmissions that’s common with the existing FreeDV software. Unfortunately, I wasn’t able to get this working on Linux during my testing as something was still keeping file handles open and not in an EOF state (despite my efforts to force the latter).

Regardless, I was able to get enough of a prototype working (along with instructions) to have a two way communication with Walter K5WH, audio of which is below:

Several other users in the test campaign were also able to successfully set up this prototype and have two way contacts as well, helping to prove out RADAE in real-world conditions. We did discover that some of us were accidentally using voice keyer files encoded at 8 kHz sample rate, which impacted audio quality on RADAE (since it was trained on 16 kHz samples).

Additionally, for the above contact (and other testing done during the campaign), Speex noise suppression was disabled. This caused some background noise to enter my side of the contact. One possible future avenue of investigation is the use of rrnoise for noise suppression instead of Speex, as it promises better performance than the latter.

Next up on the list is to actually integrate RADAE in a manner that doesn’t require significant setup (i.e. by just installing FreeDV as is the case today). This will require at least an API wrapper written in C/C++ to accomplish, with possibly some additional C code as required to maintain reasonable performance.

More information can be found in the commit history below:

(Note that all commit logs above were generated with the following command line:)

git log --author="member@email" --after "Month 1, 2024" --before "Month 31, 2024" --all > commit.log

3 Replies to “Mooneer’s FreeDV Update – September 2024”

  1. Very good work!
    It would be great if there was a bin file for the SM1000 .
    best regards

  2. I LOVED, the k6 station’s audio the best, it was fantastic!!!! K5WH’s audio was not as good. 73, Trippy

    1. FreeDV’s recording feature records both sides of the QSO in a single WAV file. Because of this, the “local” side is inevitably going to have a higher SNR (and possibly better quality) than the “remote” side of the contact. Hope this helps!

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