In what appears to be a clever marketing trick, system and soundcard manufacturers have used the moniker "HD" and attached the words High Definition to the letters.
It really stands for Half Duplex. Since rat expects a chip set that can simultaneously send out signals while receiving them, these new devices do not get recognized. The HD devices appear to do some sort of fast switching so that the user hears and speaks apparently at the same time. I'll leave it to UCL folks to correct/add to what I've just said. Joe Joseph Stone Senior Informatics Manager Family Medicine Community Health, Medical School, Univ. of Minnesota Suite 220 Dinnaken 925 Delaware St. SE Minneapolis, MN 55414 (612) 624-3192 stone...@umn.edu