Hello List,
OK, so we have FreeDV 700D which is competitive to SSB at low SNRs.
This is comprised of the Codec 2 700C speech, powerful Forward Error
Correction (FEC), and the new OFDM modem.
I am now taking a look at improving speech quality with some new Codec 2
modes, the idea is to drop these new modes into the LDPC/OFDM modem
framework that is working so well.
Modes I am considering:
i) A higher quality mode in the 2400 bit/s range. Maybe wideband audio.
We could get this into 2000 Hz of RF and SNRs of less than 10dB.
2400 bit/s would also be useful for UHF/VHF work, if competitive to FM
and AMBE.
ii) Improving the 700C Codec quality, in particular robustness to
different microphones and speakers.
Here is a first pass, comparing Codec 2 1300 (the codec used for FreeDV
1600), a simulation of SSB at 10dB SNR, and a prototype of a new 2400
bit/s (ish) mode:
http://rowetel.com/downloads/codec2/proto/
Readers who are fans of SSB noise cancellation, please run the SSB
sample through your system and post results here.
Cheers,
David
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