Hi Jim, you mention using wider bandwidth at VHF but this isn't a realistic option for use in IARU region 1, where 12.5 KHz channel spacing was adopted back in 1996. It was always worrying that Bruce repeatedly referred to 9K6 data rates for his DV codec work but wasn't able to demonstrate a method to squeeze the data stream into a 12.5 KHz channel.
By using an AMBE chip and 4800 bps, D-Star DV just about fits into 12.5 KHz; take a look the work of the Utah VHF Society. The AMBE development work took place nearly two decades ago, so it doesn't seem unreasonable to expect any subsequent DV work to match this achievement or to significantly better it. At the most recent spectrum management meetings, there was a push for 6.25 KHz working to be introduced in IARU region 1. If Codec2 can deliver better spectral efficiency than the AMBE chipset, there will be a great demand to implement it within 6.25 KHz channel spacing systems. If Codec2 requires 9K6 and/or > 12.5 KHz then it will be just another technical solution, looking for a problem to solve. It seems strange to spend so much time getting torqued up about a codec when real effort could be put into exploring the design of the next generation of DV, perhaps with TDM (multiple users occupying the same RF channels by using a "time slicing" algorithm). Like you, I am cynical that anything will emerge from Codec2 soon but never say never and good luck to the team. 73 de Darren G7LWT On 11 June 2010 04:03, J. Moen <[email protected]> wrote: > > > When talking about DV hardware approaches, I have no problem with D-STAR's > use of the proprietary AMBE coded that sells for about $20 per chip in small > quantities. It was chosen because it was the best codec available. Most > other DV systems use AMBE chips too. > > But when talking about DV software approaches, the AMBE chip does limit > development, not so much because it's proprietary, but because you can only > get it at that inexpensive price on a chip. This greatly limits > experimentation. > > So a couple of new codecs legally available to amateurs would be very > welcome. David's codec2 web page also points out the value for amateur > satellites of having open code that could be uploaded to the sats. > > He advocates at least two new codecs, one with better audio quality and > wider bandwidth for use on VHF+, the other using narrow bandwidth (like > MELP) for HF. > > If this really happens, there will be a lot of happy amateurs worldwide. > But I am skeptical that it will happen anytime soon. We are told it is very > hard to write quality, workable codecs that work in a reasonable bandwidth. > David's site currently conjectures how to go about this archtecturally, but > this project needs more than good plans and good intentions. But, I wish > him luck. > > Jim - K6JM > > > ----- Original Message ----- > *From:* a cutler22 <[email protected]> > *To:* [email protected] > *Sent:* Sunday, June 06, 2010 5:18 PM > *Subject:* [DSTAR_DIGITAL] Codec2 development - open source vocoder > > Some of you may have heard of "codec2": www.codec2.org > > David Rowe, VK5DGR has been working on its development - it is an open > source alternative to the closed AMBE chip required for the current version > of the DSTAR protocol. His development site is: > http://www.rowetel.com/ucasterisk/codec2.html > > Current development status is available here: > http://www.rowetel.com/ucasterisk/codec2.html#plan > > He is currenty looking for assistance, either financially or coding. > Because of financial obligations he's had to take a hiatus from development > to pay bills with other work. > > His email is: [email protected] > > The prospect of an open-source vocoder, ham-developed would open a lot of > doors in the way of experimentation, and reduce the $$$ barrier. A DSTAR > protocol implementing Codec2 Digital Voice would significantly drop the > entrance and appeal to a much wider audience! > > -73 de Anthony, KE7HQY > > >
