Hi Alfred, > In local experiments, I have heared, that the codec 700c sounds quite > comparable with the 1600, the audio is quite "voluminous" in contrast to > 700 and 700b. To me, this is a question only of the features of the > codec2 but not of the modulation. Is that true?
True, with no channel impairments there are no bit errors and the codec performance determines the speech quality. > On the other hand, the modulation decides, wether the codec2-data can be > successfully decoded even in critical HF conditions. Is it true, that > the decoding mainly depends on the demodulation capability of the > selected modulation? True, the modem performance is a big factor in how it handles difficult channels like HF. > Is it true then, that one can concentrate on the modem technique for > best HF results? Or is the relation between the codec2 and the modem so > entangled, that one has to see both at the same time? I tend to move back and forth between development of the codec and the modem. For example a 700 bit/s codec gives us more energy/bit than a high bit rate codec, and makes techniques like diversity possible. As we have control over both the modem and the codec, we have a better chance of developing an optimal system. > The question arouse, when Helmut and I used the codec2 in 700c, but > switched from 700c to 800xa, which in my understanding is just a > different modem, not a different codec2. Yes 700c and 800xa use the same codec, but different modems. 700b and 700c use different codecs, but same modem. What would be useful for me is a recording of the the FreeDV 700C signal you receive off air in wave file format. In particular at a SNR that is just "breaking" the mode. I can then replay this here. Gerhard also send me some samples recently - thanks Gerhard. I will also work on "instrumenting" the FreeDV 700C mode so we can measure performance as it runs. Cheers, David ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
