Hi Bruce,
Yes. I'm still alive. :-)
As it has been quite busy at work, I try to use my time coding instead
of posting/reading the lists.
I have been rewriting the modem and the additional tools a couple of
time with the goal to make them more generic and less dependant on one
particular platform. The audio-tools (i.e. to do capture/playback of the
voice) now run on portaudio and do samplerate conversion (I noticed that
a lot of the USB audiodongles do not support 8Khz sampling).
That code is already on github.
For the modem, there is a kind-of pre-alpha version of it using
portaudio (which would mean it should run on other platforms, like on
MacOSX), but the main change I am working on now so that I am converting
it into an API. There has been a request to get the GMSK modem
incorperated into FreeDV.
I have not done this kind of programming before so this is a bit new to me.
One of the advantages is that it should also make the modem more
modular, and this should make it more easy to replace certain parts of
the code (like the modulator, FEC-code, ...) and therefor would make it
a lot more easy to use it for experimenting with different protocols,
modulation methodes, FEC systems, ...
Anycase, once the API is ready and I have a test-application, I will
probably post a message if something is willing to evaluate it. I have
never written an API before and I think it will be to much designed for
my style of programming instead of a "generic" API design.
BTW.
One of the things I have in the back of my head is to convert the modem
it to a GNU radio module. I currently have no idea how to get started
with that. Does anybody think if this would be usefull or not?
I image it would make sence to simulate new versions of a protocol.
Does anybody have any experience with this? How easy / difficult is this?
So, yes ... I'm still alive, still enough to do and enoughj plans; but
sometimes, writing a modem is more about dealing with the "programming"
stuff and dealing with issues like the RPi dropping audio frames or
dongles not supported certain samplerates then with developing the modem
itself. :-(
73
Kristoff - ON1ARF
On 10-02-13 21:05, Bruce Perens wrote:
Hi Samuel,
Since this an an Open Source project we're not really worried about
"conflict" with our GMSK modem, we expect to have many modems.
Actually, that developer may have gotten busy as he's not posted to
the list for a while. Our assumption has been that the VHF/UHF radios
would be purpose-built, and I am hoping to show a prototype portable
VHF/UHF SDR at Hamvention. GMSK might be most appropriate for that.
But a mode that can be carried over FM radio audio is of course
useful. I'd encourage you to contribute the code under an Open Source
license.
Thanks
Bruce
On 02/10/2013 10:38 AM, Samuel Hunt wrote:
Hi all.
I have for some time been looking for an alternative to the "AMBE" type
vocoders which seem to dominate the low bitrate arena. Having found
Codec2, I am very impressed with the quality. Being open source is the
main interest, however.
I have had much experience with VHF/UHF data, and have devised systems
for RTK (Differential GPS), which is in use by one of the top 5
Agricultural manufacturers.
I also have much experience with VoIP, having developed my own higher
bitrate (8kbit/sec) codec.
I have been thinking for a long time about a project similar to this,
but have never had the time nor the inclination to get involved with
developing low bitrate codecs. However, I have a great deal of interest
in the lower bitrate data side of things.
I notice that you have already started on a VHF modem, which appears to
use GMSK. I guess you have selected GMSK because at 2400 baud it would
permit 6.25khz channel spacing?
I have always been more of a fan of FFSK, particularly 2400 baud,
because it readily passes through existing transmitters, receivers,
repeaters, etc, without any real modification, and seems to be more
forgiving than GMSK.
I also have written my own Windows 2400 baud FFSK modem, with error
correction, etc, for other projects, and this could probably be easily
interfaced to the Windows Codec2 DLL.
I also have experience with PIC programming, and see huge potential with
this codec ported out to a DSPIC, with a modem on the end.
I make PCB boards, etc, and own a commercial production facility, so
would also be interested in looking into porting to DSPIC and making a
nice little PCB to go into radios to retro-convert them to digital.
Anyway, I do not know if any of this is of any interest to anyone on the
list. I think what you are doing is great, and would be more than happy
to look at making a 2400 baud FFSK Soundcard based interface for this
Codec2. It would obviously work best with an external circuit to switch
audio around.
However, I suspect that this would conflict with the GMSK modem you are
already working on?
Sam Hunt
------------------------------------------------------------------------------
Free Next-Gen Firewall Hardware Offer
Buy your Sophos next-gen firewall before the end March 2013
and get the hardware for free! Learn more.
http://p.sf.net/sfu/sophos-d2d-feb
_______________________________________________
Freetel-codec2 mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/freetel-codec2
------------------------------------------------------------------------------
Free Next-Gen Firewall Hardware Offer
Buy your Sophos next-gen firewall before the end March 2013
and get the hardware for free! Learn more.
http://p.sf.net/sfu/sophos-d2d-feb
_______________________________________________
Freetel-codec2 mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/freetel-codec2
------------------------------------------------------------------------------
Free Next-Gen Firewall Hardware Offer
Buy your Sophos next-gen firewall before the end March 2013
and get the hardware for free! Learn more.
http://p.sf.net/sfu/sophos-d2d-feb
_______________________________________________
Freetel-codec2 mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/freetel-codec2
