Hi all, There are experimental FreeDV 1.8.0 builds now available that introduce two new possible modes as well as modifications to the existing 2020 mode. From the updated user manual:
1. Compression (clipping) of the 2020x modem waveforms has been added, which is worth about 4dB. This should also improve the original FreeDV 2020 mode. The Clipping checkbox is located on Tools-Options-Modem. As per the other warnings in this manual please make sure you transmitter can handle the higher RMS power. 2. 2020A uses the same waveform as 2020, but an unequal error protection scheme. The most important 11 bits of the 52 bit LPCNet codec payload are heavily protected, the other bits not protected at all. This changes the "slope" of the speech quality against SNR curve. Compared to 2020, it may work (with poor speech quality) at lower SNRs, but still have a few audible errors even at higher SNRs. 3. 2020B is like 700E to 700D - it works with fast fading but requires a few more dB of SNR. This will make it usable in European Winter (or over the South Pole Argentina to Australia) type channels - if you have enough SNR. The challenge with this mode is squeezing all the information we need (enough pilots symbols for fast fading, LPCNet, FEC bits) into a 2100 Hz channel - we are pushing up again the edges of many SSB filters. It also uses unequal FEC, just the most important 11 bits are protected, but not as well as 2020A. Note that these modes may or may not be included in future releases depending on how well they perform in live on the air use. Multi-RX is also disabled for 2020A and 2020B; selecting those modes before pushing Start will cause FreeDV to only decode the selected mode. Comments and other feedback would definitely be appreciated. Having said all of that, Windows and macOS builds are available at https://www.dropbox.com/sh/qbkt4hq32e3wx4b/AACvuWyJPkYOmeR_1V4e4rV6a?dl=0 and for those on Linux, the pull request at https://github.com/drowe67/freedv-gui/pull/211 can be built to get these modes. Thanks, -Mooneer K6AQ
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