I a working on such a scheme for PSKmail, with tables of 32k standard words (1 for each language), each word huffman coded as 2-3 bytes for downloading mail over a 100 Hz link. Experiments have shown that this is the maximum compression which can be accomplished.
73, Rein PA0R By the way, the Commodore C64 already featured an excellent text-to-voice program called Software Artificial Mouth... > -----Ursprüngliche Nachricht----- > Von: digitalradio@yahoogroups.com > Gesendet: 12.10.06 01:00:07 > An: digitalradio@yahoogroups.com > Betreff: Re: [digitalradio] Re: Digital Voice: Some thoughts after one week. > Hello Rick, > > > > >Does anyone have any "inside" information that would suggest that we > >will be able to lower the required S/N ratios for a given speed or are > >we already too close to the Shannon Limit as it is? > > The only solution to do voice exchange with a low S/N would be to translate > all the pronounced words in symbols (through some program able to > "understand" voice, the symbols being phonemes or words), to code these > symbols through a Varicode with, for example 40.000 different symbols, to > transmit these symbols and to reverse the process at reception: decoding of > the symbols and pronunciation through an auxiliary program handling an > artificial voice. > > The transmission mode would be some MFSK16 or Contestia mode (rapid and > reliable). > > > > I have listened some test in spanish with artificial voice reading words. It > was not too bad. The real problem is to translate voice in symbols, in a > reliable way. > > > > I think that, in this way, the compression of the information would be close > to the maximum. > > > > 73 > > Patrick > > > > ----- Original Message ----- > > From: KV9U > > To: digitalradio@yahoogroups.com > > Sent: Wednesday, October 11, 2006 10:54 PM > > Subject: Re: [digitalradio] Re: Digital Voice: Some thoughts after one week. > > > > > > The one common theme I see with much of the digital modes that require > the higher level of speed is that the required minimum S/N ratio hovers > around 10 db S/N. It seems to be true with DV voice, with SCAMP, and > also with high baud rate modes (such as trying to exceed a few hundred > baud on HF). > > To me there is a dividing line between real time voice and high speed > digital texting vs. slower modes that get through under difficult > conditions. Actually, difficult conditions tend to be more of the norm > on HF. > > Does anyone have any "inside" information that would suggest that we > will be able to lower the required S/N ratios for a given speed or are > we already too close to the Shannon Limit as it is? > > If we can not do this, I don't see how any of the higher speed digital > modes will ever be able to replace analog communications for weak signal > and general amateur radio communications with modest power levels and > modest antennas. In other words, what most of us do most of the time. > > Of course this would not be true for VHF and up, only for the restricted > BW's of HF. > > 73, > > Rick, KV9U > > DuBose Walt Civ AETC CONS/LGCA wrote: > > >Ed, > > > >Back in the fall of 1989, we started using a unit called the TacTerm for DV. > >The best modem was a 39 parallel tone modem (Mil-Std-188-110?) and 2400 BPS. > >On HF it sounded funny...robotic like...and while it did work on about the > >same SNR as a ~S3 SSB signal ...the SNR had to be about 10 dB, it worked > >much better on VHF and UHF FM as well as UHF AM. > > > >In Jan-Feb 1990, after Operation Just Cause, I got to play with a Harris > >Mil-Std-188-110? modem and DV at 2400 BPS AND 4800 BPS. The 2400 bps DV > >still sounded a bit robotic but worked quite well at S2-S3 signals and even > >when the SNR was at or I think slightly below 10 dB. The modem had ALE and > >provided a SNR figure and my old ham radio ear figured an S2-3 signal. > > > >When we switched to 4800 bps, the DV sounded just like the individual > >speaking over a telephone...better than SSB voice but it required a slightly > >better SNR. > > > >Data with the TacTerm 39 tone modem was really good...text came through at > >about a page a minute with a signal that you could hear. When the signal got > >down close to the noise...where you had to strain to hear it, the throughput > >went down to maybe 20-30 lines per minute....but still near 100% copy (could > >have been typing errors). The actual computer software was KA9Q NOS running > >on a BIG military laptop computer. > > > >When we went to the Harris modem and 2400 BPS/4800 BPS, the copy at 2400 BPS > >was about the same with a good signal but better than the TacTerm with lower > >qualitity signals. > > > >4800 bps screemed unless the signal got below 10 dB SNR or so. > > > >During Operations Desert Shield and Desert Storm, the U.S. Marine Corp used > >a Hughes RT-1209 and Harris AM-6545A 400 watt amplifier to make up the > >GRC-193A (http://www.nj7p.org/millist/pic/grc-193.gif) used in some of the > >last productions Jeeps and Humvees. Most were using a 15-16 ft fold over > >whip. The whip went up just about 18" higher then the Humvee top and then > >tilted over and ran horizontal the remainder of the length. This provided a > >good NVIS antenna radiation pattern. > > > >The Marine Corp did connect the Harris MIL-STD-188-110x modem to the GRC-193 > >and used a computer to send data from the field back to their command center. > > > >For digital voice I believe that some units used the Navy's version of the > >TacTerm and some may have been using the later ITT MinTerm DV unit. The > >TacTerm (KY-57) can accept signal fades of up to 12 seconds without losing > >synchronization with the transmitting station. > > > >I never noticed any delays or words that were not understandable using the > >TacTerm or MinTerm or Harris Modem using LCP-10 and UG-??? encryption unit. > >There were of course a second or two between transmissions, but certainly > >not enough to prevent artillary spotting or fire control. > > > >The PRC-109/GRC-193 systems were used at least in 1985 and perhaps before > >with the TacTerm. The TacTerm was used in the Viet Nam war on HF SSB, VHF > >and UHF AM and as far as I know without problems. The C-130s tracking and > >Navy vessel captured by North Korea used Tacterm's on HF and the crew of the > >C-130 never mentioned to me that there were communications using the TecTerm. > > > >So when the Marine Corp have problems with DV must have been shortly after > >the capture of the USS Pubelo which I believe was in 1968. > > > >A good reference on the ANDVT modem may be _HF modem evaluations for the > >Advanced Narrowband Digital Voice Terminal (ANDVT)_ by Chase, D.; Bello, P. > >A.; Boardman, C.; Pickering, L.; Pinto, R. published in Nov 1978 > > > >Abstract: > >"During this program, the specifications for the ANDVT HF modem have been > >refined and detailed evaluation and simulation of the new technical features > >within this modem have been conducted. These include a multiple-tone signal > >detection format with an adaptive threshold, a multiple-tone/multiple-stage > >Doppler estimation algorithm, a matched filter frame estimation algorithm > >utilizing PN correlation properties, a low-rate error-correction coding > >approach for protection of the KG sync sequences, an error-correction coding > >approach specifically designed to protect the critical speech parameters, > >use of soft-decision (channel measurement) information obtained from the > >demodulator, and decision-directed Doppler tracking utilizing information > >from all data tones. The analytical and simulation results provide the > >desirable result that the preamble can be successfully received at a lower > >SNR than is required for the reception of high-quality 2400-b/s digitized > >voice." > > > >Walt/K5YFW > > > > > > > > > -- http://pa0r.blogspirit.com Need a Digital mode QSO? 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