Justin, VK7TW, has published a video of my recent presentation at the Gippstech conference:
https://www.youtube.com/watch?v=nAJ9s2Di084 Good summary of FreeDV, the SM1000, and the exciting possibilities for VHF Digital Voice. Thanks Justin :-) - David On 03/08/15 10:11, Jean-Marc Valin wrote: > Any reason you can't just use the Speex resampler? It's implemented in > both fixed-point and float, has reasonable complexity (with a quality vs > CPU knob) and it's easy to rip out of the Speex source code. The > resampling ratio can be any rational number, so 7500 Hz is no problem. > > Cheers, > > Jean-Marc > > On 08/02/2015 08:33 PM, glen english wrote: >> I'll do this. easy. >> >> Interpolation is usually cubic. Leave that up to me. >> >> There wouldnt be any implementation loss. just a few more MIPS. >> >> platform ? >> >> though, I would STRENUOUSLY suggest changing the modem symbol rate. >> >> 7500 Hz is .. well, a pain ....and will be a pain forever unless it is >> nipped in the bud now. >> >> >> >> On 3/08/2015 10:03 AM, David Rowe wrote: >>> Thanks Glen, >>> >>> We are stuck with the 7500Hz for the moment (an integer ratio of the >>> modem symbol rate, details in octave/cohpsk_frame_design.ods). >>> >>> Yes I had in mind something like your latter suggestion, up sample to 16 >>> kHz, then linear interpolation. It would need to be tested in terms of >>> modem implementation loss. >>> >>> However I know what needs to be done, brainstorming that is the fun >>> part. What would be wonderful is someone stepping forward to carefully >>> code and test. >>> >>> Any volunteers? I'll work with you to help code, review, and test. You >>> need C coding skills with an interest in DSP, some time, and determination. >>> >>> Thanks, >>> >>> David >>> >>> On 03/08/15 09:09, glen english wrote: >>>> David >>>> for resampling... >>>> >>>> so you want to go from 8000 to 7500 Hz ? >>>> >>>> I've always picked my modems to be integer divisors of 48k . makes life >>>> easy. >>>> However, if we are stuck with 7500... >>>> >>>> 1) SRC using 120kHz as the common sample rate (polyphase resampler >>>> interpolator/decimator) >>>> cleanest, highest MIPS usage, easiest to understand. >>>> >>>> 2) Farrow interpolator. >>>> Best if passband is a small fraction of the sample rate. >>>> Most used for fractional sample rate conversion for mismatched clocks. >>>> >>>> A counter is used counting samples in and out, the fraction determined, >>>> and the resampling FIR coefficients are calculated on the fly. >>>> >>>> given a big chunk of the Nyquist BW is used, perhaps upsample to 16k , >>>> convert to 15k, >>>> and then crash-downsample/undersample to 7500 (cheap). >>>> >>>> >>>> -- >>>> >>>> I can do this. >>>> --- >>>> >>>> >>>> >>>> On 3/08/2015 9:20 AM, David Rowe wrote: >>>>> Further to this thread (started on the digitalvoice list) James has >>>>> provided a patch to implement his suggested changes to the FreeDV API, >>>>> which is now checked into codec2-dev. >>>>> >>>>> So wonderful for me to have some one step up and contribute some code. >>>>> >>>>> Thanks James! >>>>> >>>>> Now I need to go to work on the FreeDV GUI program to support these >>>>> changes. >>>>> >>>>> Down the track I'd like to see the FreeDV API accept a 8000 Hz sample >>>>> rate for the 700 mode (its currently 7500Hz). I have some ideas on how >>>>> to do this if anyone would like to work on the C code. But right now my >>>>> focus is on tuning the FreeDV 700 mode. >>>>> >>>>> On that subject I'm getting some great reports from people working >>>>> across the Atlantic on FreeDV 700 on as little as 5W - thanks Gerhard, >>>>> Walter, and Mel! The new modem is really working well on the HF fading >>>>> channel, and we have several examples of 80% DV copy when SSB was >>>>> unusable. I feel the speech codec needs some work, but we will get there. >>>>> >>>>> Exciting times for HF DV! >>>>> >>>>> - David >>>>> >>>>> ------------------------------------------------------------------------------ >>>>> _______________________________________________ >>>>> Freetel-codec2 mailing list >>>>> [email protected] >>>>> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >>>>> >>> ------------------------------------------------------------------------------ >>> _______________________________________________ >>> Freetel-codec2 mailing list >>> [email protected] >>> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >>> >> > > ------------------------------------------------------------------------------ > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > ------------------------------------------------------------------------------ _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
