Codec2 is an awesome, new, award
winning, free as-in freedom, open source, digital voice codec. Codec2
was developed primarily by David Rowe Ph.D., VK5DGR, specifically to avoid
the intellectual property encumbrances of the digital voice codecs
currently in use.
By now you've probably heard of D-STAR.
What you may not know is that the voice encoding protocol (codec)
used by D-STAR, AMBE, is a proprietary patented trade secret.* Under
no circumstances may you inspect, dissect, examine, or modify the
codec. This is not in the spirit of amateur radio! Unfortunately most
of the other digital voice codecs in use today suffer from similar
encumbrances.
In 2008, well-known open source
advocate and Amateur Extra Bruce Perens, K6BP, recognized the danger
of closed codecs, and began to advocate and evangelize the need for a
free as-in freedom codec for hams. Thankfully, Bruce was able to
recruit successful open source codec developer David Rowe to our
cause. David has an impressive and extensive digital voice resume, and he co-developed the Speex codec, one of the most popular VoIP codecs on the
Internet today.
Dave et al have designed Codec2 and
created a free open source reference implementation, released under
the GNU Lesser General Public License, meaning that it's free and
easy to incorporate into other software, even commercial
applications. The reference implementation is written in C and
targets Linux, with work on Windows compatibility underway (Cygwin is
already supported). I was able to download it and easily compile it
on my Ubuntu Linux box and encode/decode some sample audio files. I
think it sounds GREAT, even at it's narrowest bandwidth!
The reference implementation includes
an FDMDV softmodem optimized for use with Codec2. Remember that a
codec converts one digital stream to another digital stream; it must
be modulated on an analog signal to be transmitted over the air. The
FDMDV modem works with your sound card, much like PSK31 or SSTV, and
is optimized for HF. The FDMDV modem may also be used with VHF+ FM
radios, although an optimized GMSK modem is planned for such
operation.
Not only is Codec2 free, but David has
managed to produce a codec of truly superlative technical quality. On
HF, Codec2 bandwidth is as narrow as 1.1khz; HALF of SSB! On VHF+,
3kHz channels should be easily attained, with 2kHz channels possible
depending on radio quality. That's ½ to ¼ the bandwidth of other
popular codecs such as AMBE. Power efficiency is easily double that
of existing codecs, and hence range is substantially improved. Sound
quality is excellent for a voice codec. Depending on the modem used
with the codec, amplifiers may be non-linear, hence cheaper and more
efficient. The bottom line is that Codec2 beats the snot out of all other digital radio voice codecs!
Because Codec2 is a free and open
specification, it is not an “unspecified digital code under
FCC rule 97.309(b)”, and may be legally used for international
communications. Contrast this with the situation in France, which has
completely banned D-STAR due to the closed nature of AMBE.
On July 24 the ARRL announced David
Rowe as the recipient of the 2012 ARRL Technical Innovation Award for
his work on Codec2. The Board noted that Rowe “has been a major
leader and the primary technical author of an open-source CODEC2
protocol, designed to address the impediment to the development of
amateur digital voice posed by closed-source protocols.”
Codec2 and FDMDV are currently usable,
but are in an “alpha” stage. Development and testing are well
underway, including on the air testing. There's a GUI in the works, but right now it's just a
collection of command line utilities and libraries, so that's a bit
of a hurdle for less technical folks. I hope we soon start to see
Codec2 support in the popular PC SDR apps, and DSP radios like the K3
should be able to support it with a firmware upgrade. I for one am
looking forward to trying Codec2 on the air, and I'll be sure to
report my findings when I do.
For more information:
* If you were in the D-STAR presentation at the 2010 RANV HAMCON, you may have caught me giving the presenter, Cal Calvitto, WA1WOK, a little friendly heckling about AMBE (Sorry Cal, nothing personal, and I did enjoy your presentation). Yes, D-STAR takes a lot of heat. Yes, the
codec situation is unacceptable. It's also pretty lame that Icom
trademarked it even though JARL invented it. And the rigs cost a fortune. That said, I have reviewed the D-STAR specification, and
aside from those issues, I think it's actually a pretty good system.
If the issues can be surmounted, then I would be happy to see D-STAR
with Codec2 become widely adopted by the ham community.
1 comment:
Thank you for sharing the information.
I would like to inform that I too have recently came across a site called two-way radio who is providing the service of two-way radio for communication purpose.
Two Way Radio Accessories, TwoWay-Radio Australia
Post a Comment