Re: [DSTAR_DIGITAL] Re: Codec2 development - open source vocoder
At 11:56 PM 6/11/2010, you wrote: >The answer to why there's a push for 6.25 KHz, >could best be answered during a chat with G4TSN, >who will fill you in on how hard it is to get >new kit on the air on VHF, especially near >conurbations. This problem exists across much of >Europe and the US, it's not a local issue. It is a problem across much of the world. Here, the situation is slightly different, but again one where narrow bandwidth helps. We're pretty much our of 2m repeater pairs here in Melbourne. However, despite there being a bit of spectrum for simplex, as while we have 4MHz on 2m, unlike the US, we don't have any repeaters below 146 MHz. This leaves quite a bit of simplex room from around 145.2 (top of the digital/packet sub band) to 145.8 (bottom of the satellite segment), minus a couple of "special purpose" frequencies (ARDF/foxhunting, Morse practice beacon, RTTY). However, this simplex room is quite full, with several IRLP/Echolink nodes, as well as various clubs and groups, who regular use simplex frequencies. In fact, the simplex part of the band is often busier than the repeaters down here. Even with D-STAR's (effective) 12.5 kHz bandwidth, we're able to slip D-STAR in between the 25 kHz spaced FM channels. 6.5 kHz bandwidth would make this even neater. >TDM would have the benefit of reusing the >precious spectrum (see above) and the valuable >hill top sites/equipment, that volunteers spend >so much effort financing and maintaining. TDM could be particularly valuable for repeaters, especially as sites become more limited in availability, so if one site can carry more than one stream of traffic, that would work to our advantage. >TDM is also something to experiment with. To >say, "Why do TDM?", could encourage others to >say, "Why do sound card based GMSK?". Both of >the items above are valid for experimental >purposes and self training. There are >undoubtedly many amateurs that have not worked >on TDM systems professionally and some might >enjoy learning about TDM, just as some amateurs li >ke to use a PC, soundcard & software to do the >job of a GMSK modem chip and a PIC. That's a good enough reason for me to play. In this part of the world, we'd also be looking at playing with methods to increase the coverage area of TDM, such as optimising the duration of the time slices and pre-compensating for propagation delay. This was one of the well known limitations of GSM, the 30-35km cell radius limit (of the basic GSM system, without any cell extenders). Open terrain and low population densities meant this became a real issue in rural areas. >As it happens, there is already a well developed >open source stack for GSM that could be adapted >to our needs... but now we're heading rather OT. That would be a good starting point. Hmm, maybe we need to move to another digital voice experimenters group. ;) >I agree that Codec2 is a neat project and one to >be encouraged. Whether Codec2 has any place >within D-Star or even if D-Star will still be >the preferred DV mode when Codec2 matures, are >entirely different questions altogether. I agree. I can't see Codec2 and D-STAR having any significant roles together (because of the amount of D-STAR gear already out in the field), but I do see Codec2 as having a lot of potential for experimentation, particularly in new VHF/UHF modes, as well as HF DV, if the developers can get the bitrate into the 1000bps and below region (to make Shannon's Law work in our favour). Codec2 will allow the next generation of DV modes to be developed on a PC, which is a low cost way of getting a lot of people into the mode. Look at what PCs did for PSK-31 and SSTV years ago. 73 de VK3JED / VK3IRL http://vkradio.com
Re: [DSTAR_DIGITAL] Re: Codec2 development - open source vocoder
Hi Jonathan, fortunately the AMBE chip is so efficient that we don't have to start running QPSK/OFDM and changing over to ultra linear PAs, like we have for Digital ATV. It seems churlish to suggest that everyone change their radios, repeaters and power amplifiers, just to cope with the deficiencies of open source codecs. The answer to why there's a push for 6.25 KHz, could best be answered during a chat with G4TSN, who will fill you in on how hard it is to get new kit on the air on VHF, especially near conurbations. This problem exists across much of Europe and the US, it's not a local issue. TDM would have the benefit of reusing the precious spectrum (see above) and the valuable hill top sites/equipment, that volunteers spend so much effort financing and maintaining. TDM is also something to experiment with. To say, "Why do TDM?", could encourage others to say, "Why do sound card based GMSK?". Both of the items above are valid for experimental purposes and self training. There are undoubtedly many amateurs that have not worked on TDM systems professionally and some might enjoy learning about TDM, just as some amateurs like to use a PC, soundcard & software to do the job of a GMSK modem chip and a PIC. As it happens, there is already a well developed open source stack for GSM that could be adapted to our needs... but now we're heading rather OT. I agree that Codec2 is a neat project and one to be encouraged. Whether Codec2 has any place within D-Star or even if D-Star will still be the preferred DV mode when Codec2 matures, are entirely different questions altogether. 73 de Darren G7LWT On 11 June 2010 12:59, Jonathan Naylor wrote: > > > Getting 9600 Bd into 12.5 kHz isn't too difficult as long as you're willing > to sacrifice weak signal performance, Shannons law tells us that. I would > imagine OFDM or even m-ary PSK would be capable of providing the required > throughput. > > The big advantage that GMSK has for manufacturers is that they can use the > same class C output stages as they do for FM. PSK and particularly OFDM > require extremely linear amplifiers. > > If we go over to TDM then we're in the land of GSM or NexEdge > re-implementation and why should we do that? > > I think the development of codec2 should be encouraged as it represents > something fun, rather than just plugging in black boxes which seems all too > prevalent these days. > > BTW why is there a push to 6.25 kHz channel spacing, the 2m band is hardly > that busy these days. A better argument for that could have been made in the > early-80s when the channels were choc-a-bloc but not now. We almost went > 12.5 kHz then (remember S20x?) but we didn't. > > Jonathan G4KLX > > >
[DSTAR_DIGITAL] Re: Codec2 development - open source vocoder
Getting 9600 Bd into 12.5 kHz isn't too difficult as long as you're willing to sacrifice weak signal performance, Shannons law tells us that. I would imagine OFDM or even m-ary PSK would be capable of providing the required throughput. The big advantage that GMSK has for manufacturers is that they can use the same class C output stages as they do for FM. PSK and particularly OFDM require extremely linear amplifiers. If we go over to TDM then we're in the land of GSM or NexEdge re-implementation and why should we do that? I think the development of codec2 should be encouraged as it represents something fun, rather than just plugging in black boxes which seems all too prevalent these days. BTW why is there a push to 6.25 kHz channel spacing, the 2m band is hardly that busy these days. A better argument for that could have been made in the early-80s when the channels were choc-a-bloc but not now. We almost went 12.5 kHz then (remember S20x?) but we didn't. Jonathan G4KLX
Re: [DSTAR_DIGITAL] Codec2 development - open source vocoder
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 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 > *To:* dstar_digital@yahoogroups.com > *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: da...@rowetel.com > > 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 > > >
[DSTAR_DIGITAL] Codec2 Developer InterviewInterview
There's also a really great interview with David Rowe, VK5DGR that gives a lot of background on his history, extensive experience in codecs and his future aspirations. The interview is from Oct. 2008: http://www.cio.com.au/article/264806/open_source_identity_free_telephony_project_founder_david_rowe/?fp=4&fpid=51241 -73, KE7HQY
Re: [DSTAR_DIGITAL] Codec2 development - open source vocoder
Going strictly from emails I've exchanged with David, it sounds like he has some "grunt" work in C, which he could offload to someone else to take over while he focused on DSP programming, etc. Right on his website he states: "Not all of this project is DSP. There are many general C coding tasks like refactoring and writing a command line soft phone application for testing the codec over a LAN." Rather than dismiss potentially helping right off the bat, I would review his Developement roadmap: http://www.rowetel.com/ucasterisk/codec2.html#plan *and email him: da...@rowetel.com -73, KE7HQY From: Robbie De Lise To: dstar_digital@yahoogroups.com Sent: Fri, June 11, 2010 12:31:00 AM Subject: Re: [DSTAR_DIGITAL] Codec2 development - open source vocoder I know a little bit of C, no C++ though. And I think my knowledge would really not be suffice to do something like this. 73s Robbie ON4SAX On Fri, Jun 11, 2010 at 8:27 AM, a cutler22 wrote: > > > > > > > > > > > > > > > > >> > >> > >Nor do I know C that well... > > >that's why I'm getting the word out - anyone can help spread the word about >Codec2 and its development. > > >My overt zeal may have ticked a few people off, so I would recommend a more >cooler-headed approach :) > > >-73, KE7HQY > > > From: Tony Langdon > >To: dstar_digital@ yahoogroups. com >Sent: Fri, June 11, 2010 12:09:48 AM > >Subject: Re: [DSTAR_DIGITAL] Codec2 development - open source vocoder > > > > > >> > > > >>>If any of you speak the C language he could use your hand! At the >>>very least, getting Codec2 to a > >>Unfortunately, I don't. :( > >>> beta-testing stage would be exciting to say the least! However, it >>> won't happen without community support. > >>Well, when it gets to the point that some beta testing is needed, >>then I can offer my assistance. :) > >>73 de VK3JED / VK3IRL >http://vkradio. com > > >
Re: [DSTAR_DIGITAL] Codec2 development - open source vocoder
I know a little bit of C, no C++ though. And I think my knowledge would really not be suffice to do something like this. 73s Robbie ON4SAX On Fri, Jun 11, 2010 at 8:27 AM, a cutler22 wrote: > > > Nor do I know C that well... > > that's why I'm getting the word out - *anyone* can help spread the word > about Codec2 and its development. > > My overt zeal may have ticked a few people off, so I would recommend a more > cooler-headed approach :) > > -73, KE7HQY > > -- > *From:* Tony Langdon > > *To:* dstar_digital@yahoogroups.com > *Sent:* Fri, June 11, 2010 12:09:48 AM > > *Subject:* Re: [DSTAR_DIGITAL] Codec2 development - open source vocoder > > > > > >If any of you speak the C language he could use your hand! At the > >very least, getting Codec2 to a > > Unfortunately, I don't. :( > > > beta-testing stage would be exciting to say the least! However, it > > won't happen without community support. > > Well, when it gets to the point that some beta testing is needed, > then I can offer my assistance. :) > > 73 de VK3JED / VK3IRL > http://vkradio.com > > > >
Re: [DSTAR_DIGITAL] Codec2 development - open source vocoder
Nor do I know C that well... that's why I'm getting the word out - anyone can help spread the word about Codec2 and its development. My overt zeal may have ticked a few people off, so I would recommend a more cooler-headed approach :) -73, KE7HQY From: Tony Langdon To: dstar_digital@yahoogroups.com Sent: Fri, June 11, 2010 12:09:48 AM Subject: Re: [DSTAR_DIGITAL] Codec2 development - open source vocoder >If any of you speak the C language he could use your hand! At the >very least, getting Codec2 to a Unfortunately, I don't. :( > beta-testing stage would be exciting to say the least! However, it > won't happen without community support. Well, when it gets to the point that some beta testing is needed, then I can offer my assistance. :) 73 de VK3JED / VK3IRL http://vkradio.com
Re: [DSTAR_DIGITAL] Codec2 development - open source vocoder
>If any of you speak the C language he could use your hand! At the >very least, getting Codec2 to a Unfortunately, I don't. :( > beta-testing stage would be exciting to say the least! However, it > won't happen without community support. Well, when it gets to the point that some beta testing is needed, then I can offer my assistance. :) 73 de VK3JED / VK3IRL http://vkradio.com
