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 > -- - Glen English RF Communications and Electronics Engineer CORTEX RF & Pacific Media Technologies Pty Ltd ABN 40 075 532 008 PO Box 5231 Lyneham ACT 2602, Australia. au mobile : +61 (0)418 975077 ------------------------------------------------------------------------------ _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
