Monthly Archives: January 2025

FreeDV 2.0.0-20250130 released

This is the second preview release of FreeDV containing the new RADE mode. For more information about RADE’s development, check out the blog posts on the FreeDV website:

Changes versus the first preview release:

* Signal to noise ratio (SNR) is now displayed while receiving RADE signals.
* Received signals are now reported to FreeDV Reporter (without callsigns) once per second. Once a callsign is received (at the end of the transmission), the callsign is reported to both FreeDV Reporter and PSK Reporter.
* Fixed bug preventing sync indicator from turning green with RADE.
* Visual Studio Redistributable is now installed if your PC does not already have it. (This is required for the Python packages FreeDV uses.)
* Fixed bug preventing Request QSY button from being enabled in RADE mode.
* RADE has been renamed to RADEV1 in the UI and FreeDV Reporter.
* macOS binaries are now signed and notarized, avoiding the need for the workaround in the previous build.
* Fixed issue causing FreeDV to segfault on exit when RADE is running.
* Python files are now precompiled to improve startup time.
* Core RADE code is now in C (versus Python).
* Uninstaller now fully cleans up after Python.
* Audio chain is cleaned up to improve audio quality.
* README has been updated to clarify Linux instructions and to provide a link to a script to auto-build with RADE support. (Thanks @barjac!)
* Maximum SNR displayed in the main window is now 40 dB to reflect real-world testing.
* “devel” in the version string is shortened to “dev” and incremented to “dev2” to reflect the second preview build.

Limitations:

* Multiple RX mode is not supported. If you choose RADE and push Start, that’s the only mode you can work; you’ll need to stop, choose another mode and start again to work FreeDV with the existing modes.
* Squelch cannot currently be disabled with RADE. It’s unknown at this time whether disabling squelch is possible.
* Due to compilation problems, 2020/2020B modes are disabled.
* There is currently no Windows ARM build; this will hopefully be included in a future preview build. You may be able to use the 64-bit Intel/AMD Windows build in the meantime.
* Minimum hardware requirements haven’t been fully outlined, so your system currently may not be able to use RADE. Future planned optimizations may improve this.

Other notes:

* The below builds are significantly bigger than previous releases. This is due to needing to include Python and the modules that RADE requires. Planned porting to C/C++ will eventually negate the need for Python.
* The Windows build includes Python but not the modules that RADE requires. As part of the install process, the version of Python built into FreeDV will go out to the internet to download the needed modules.
* As development is expected to happen quickly, these preview builds have a six month expiry date (currently July 30, 2025).
* 32-bit Windows is no longer supported due to its likely inability to work with RADE.

More information and download links can be found at https://github.com/drowe67/freedv-gui/releases/tag/v2.0.0-20250130.

David Dec 2024 – Testing RADE with Automatic Speech Recognition

An important goal of our project is improved speech quality over SSB and both low and high SNRs. We have anecdotal reports of good performance of RADE compared to SSB, but need an objective, controlled way of comparing performance. For speech systems this generally means ITU-T P.800 or P.808 standards based subjective testing. However this is complex and requires skills, experience and resources not available to our team.

A few months ago Simon, DJ2LS suggested the use of Automatic Speech Recognition (ASR). More recently, when discussing the issue of subjective testing, Jean Marc Valin also suggested ASR and provided suggestions for a practical test system. So I spent much of December building up a framework for ASR tests.

The general idea is to take a dataset of speech samples, pass them through simulations of SSB and RADE over HF radio channels, then use a ASR engine to detect the words in the received speech. A post processing system then compares the detected words to the original words and determines the Word Error rate (WER) as a performance metric. Our work uses the Librispeech dataset, and the Whisper ASR system.

These sentences are complex English sentences, spoken quickly with no contextual cues. I have trouble understanding many of them on the first listen. This is a much tougher test than the typical low SNR Amateur Radio contact where someone shouts their callsign 5 times then reports “5 by 9”. For example, here is one sample from the Librispeech dataset processed with SSB/RADE/original (listen to the original last); SSB and RADE were at about 6dB SNR on a MPP (fading) channel.

The plot below show some initial results over 500 sentences. The x-axis is receiver SNR measured in a 3kHz noise bandwidth. The y-axis is the word error rate WER). Green is RADE, and blue SSB. The solid lines are for a AWGN channel, the dashed lines the multi-path poor (MPP) fading channel. The dots (placed arbitrarily on the x-axis) in the lower right are controls, e.g. the FARGAN synthesizer used by RADE with no encoding, 4kHz band limited speech, and the original, clean speech.

A low word error rate (WER), say 5%, would correspond to an effortless “armchair copy”; a 30% WER could be the limits of practical voice communication (1 in 3 words can’t be understood). The distance between the RADE and SSB curves shows the benefits of RADE, at least using this test.

For example, if you draw a line across the 10% WER level, RADE achieves this (dashed MPP curves) at 3dB, SSB at 12dB. The x-axis doesn’t include the PAPR advantage of RADE, which is roughly an additional 5dB when using a transmitter with the same peak power output (depending on how hard the SSB is compressed).

Also this month I have been working on SNR measurement of received RADE signals. This is quite challenging, due to the lack of structure in the ML-generated RADE constellation. At present I’m attempting to use a classical DSP approach using the pilots symbols. This will be the last feature we will add to RADE V1, as we’d like to use the lessons learned to start designing RADE V2.

Mooneer’s FreeDV Update – December 2024

This month involved more improvements to the FreeDV GUI application. One improvement involved the unit test framework; it’s now possible to capture the features decoded by RADE (prior to being fed into the FARGAN codec). This is useful for quantifying changes in the receive pipeline and ensuring that what’s encoded by RADE is also mostly returned by the decoder on a clean channel.

The biggest improvement, however, is the implementation of the same LDPC based callsign encoding and decoding system that’s used in the legacy FreeDV modes. This data is placed in what’s known as the End Of Over (EOO) block at the end of the RADE transmission and allows the application to report received callsigns to FreeDV Reporter and PSK Reporter, albeit only at the end of the transmission. FreeDV Reporter specific logic was added to mitigate this by reporting that a RADE signal is being received once a second while still in sync (just with no callsign), hopefully still allowing people to see that someone’s possibly decoding them in real time.

Since we’re touching the FreeDV Reporter logic, it was also a good opportunity to make some significant changes to the FreeDV Reporter service and website. First, the “left the chat”/”entered the chat” messages were removed by PLT request in order to make it easier to see actual chat messages. Next, the separate popup window for viewing who’s in the chat was removed in favor of an always-visible bar at the bottom of the chat tab containing the callsigns of the users that are logged into chat. The message backlog was also extended to 30 days (from 7 days) and preserved into a database so that the chat messages aren’t lost in the event that the FreeDV Reporter server needs to be restarted.

Besides the above, there were some other minor fixes with the Windows installer/uninstaller along with logic added to detect whether microphone permissions have been granted. RADE is also now called RADEV1 in the FreeDV application to differentiate it versus a future version 2 of RADE. Some infrastructure was also added to be able to sign macOS builds (required to avoid errors involving “damaged” applications in newer versions of macOS).

In any case, we’re now going to focus on additional testing prior to releasing a new preview build of FreeDV for general usage. Hopefully we’ll have additional updates on that soon.

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