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So the on-air audio might suffer some with the new version. Pearce said that none of the available open-source codecs work as well as the old one: ' MELP, or Mixed Excitation Linear Prediction, was designed specifically for high-quality, low data-rate voice communication. FDMDV works with weaker signals than WinDRM.' The main problem with HF digital voice is that it needs fairly strong signals. They both use OFDM modulation, a set of close-spaced carriers that are each modulated with a little bit of data to add up to the final digital signal. FDMDV sounds a little rougher, but uses only 1.1 kHz of spectrum. WinDRM, the best sounding program, uses 2.5 kHz of spectrum. Pearce said these three programs all allow hams to transmit and receive digital voice by connecting their PC sound card to an ordinary SSB transceiver: 'The result has been surprisingly high quality audio, with virtually no noise - sort of like listening to FM, but in the narrow bandwidth of a sideband signal. WinDRM could always use the open-source Speex codec, but FDMDV users will need to download the new version.' ' DRMDV, an intermediate program between the other two, has been abandoned. 'Lanza did a quick rewrite to use an open-source codec, and now WinDRM and FDMDV are back,' Pearce said. According to Gary Pearce, KN4AQ, the companies have 'winked' at ham radio use for several years, but a recent complaint caused the programs to be pulled from the download site.

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Rights to various forms of the codec are held by several companies they have never been released for free distribution and use by hams. WinDRM, DRMDV and FDMDV, all written by Cesco Lanza, HB9TLK, used a codec that was developed for the US Department of Defense and NATO.

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Citing codec (coding/decoding) licensing issues, three free Windows programs for sound card-based HF digital voice were yanked from their download site for a short time recently, surprising hams who are interested in HF digital voice operation several online groups that supported the software were also closed for a short time.

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