I've simulated adding a powerful, but reasonably short, LDPC code developed by Bill vk5dsp to Codec 2 700C. Early days, but looks like a 5dB improvement on a HF channel:
http://www.rowetel.com/?p=5485 Next step is porting to a new FreeDV 700D mode that can be tested over the air. - David On 18/03/17 16:08, David Rowe wrote: > Hello Steve, > > Listening to the unquantised vocoder model is a good test. If the > quantisers are perfect, then the quantised and unquantised should sound > the same, but usually we trade off some quality in that step. > > There is also some resampling going on, like moving between 10 and 40ms > frame updates. > > c2sim can be used to simulate various stages of quantisation, for > example completely unquantised, codec 2 model: > > $ ./c2sim hts1a.raw -o - | aplay -f S16_LE > > is very high quality, and consists of one amplitude and phase for each > harmonic, and the number of harmonics is time varying. > > I have attached the (unquantised) _uq versions for comparison to 1300. > > Cheers, > > David > > On 18/03/17 15:06, Steve wrote: >> Well, the weird experiment today, was to remove all of the Codec2 >> quantization, so I could hear what it sounds like before high >> compression. >> >> It definitely sounds like a vocoder even sans compression :-) >> >> Instead of packed bytes I just sent a class (structure) back and forth >> with all the parameters as floats or booleans. Billions and billions of >> bits per second :-) >> >> Codec2Test <https://github.com/ObjectToolworks/Codec2Test> >> >> Alas, it's Java, but it's a way to rapid application development for me. >> I started with the 1300 vocoder, and then removed all the quantization >> stuff. >> >> The thing is, I think the raw vocoder sounds a lot like 1300 mode. That >> is, most of the warble is already there before the compression and bit >> errors. >> >> Now admittedly, the Java code might not be perfect, so there is that >> error to think about. >> >> Steve >> >> >> >> ------------------------------------------------------------------------------ >> >> 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 >> > > > ------------------------------------------------------------------------------ > 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 > ------------------------------------------------------------------------------ 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
