ARLA/CLUSTER: WinDRM, DRMDV e FDMDV mudam os códigos por causa dos direitos de autor.

[João Gonçalves Costa]

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WinDRM, DRMDV and FDMDV sound card programs get codec change

Several popular digital voice programs that were pulled from distribution have returned with a different digital coding and decoding scheme. This following major rewrites to avoid problems dealing with intellectual property rights.

Amateur Radio Newsline's Gary Pearce, KN4AQ, is in Cary, North Carolina, with the details:

Hams who tried to download any of the sound-card based Digital Voice programs - WinDRM, DRMDV and FDMDV - this past week, found them gone, as were the Google-Groups message boards that supported them.

The problem was licensing, or lack of it, for the codec that all the programs shared. That codec was developed for the US military and NATO, but was never licensed for free distribution. Several companies shared the intellectual property rights, and finally, one of them complained.

This caused a quick re-write of WinDRM and FDMDV with an open-source codec. At air-time, the new version of FDMDV was available again at the download site, N1SU dot COM, and WinDRM is expected to be back soon. DRMDV, little used since FDMDV was developed, has been dropped.

Digital Voice users will need to download the new version of FDMDV to maintain compatibility.

The new codec isn't quite as good as the old one, so audio quality, a hallmark of the Digital Voice programs, will suffer a bit. The old codec, called MELP, was designed for high quality, low data-rate communication, and was particularly well suited for HF radio applications.

WinDRM occupies about 2.5 kHz of spectrum and sounds like FM with few artifacts when signals are good. FDMDV, uses only 1.1 kHz of spectrum. It sounds a little rougher, but still remarkable for that low bandwidth. It works closer to the noise level, and has almost no latency. Both programs use OFDM multiple carrier modulation schemes, and work with ordinary single-sideband transceivers.

This episode points out the need for someone - somewhere - to develop a codec for low-bandwidth digital voice on Amateur Radio. The sound-card based digital-voice programs have been a continuous "work in progress." But they need a codec for that work to continue.

Note that the AOR digital voice modems, and D-STAR radios, use a commercial product, the AMBE 2020 vocoder, so they are not affected by this license situation.

Gary Pearce, KN4AQ

Fonte: Amateur Radio Newsline
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