[WARC] Fw: Exerpt from the ARRL Letter, Vol 27, No 30 (Friday, August 1, 2008)

[Leslie Hittner]

Thought I would pass along this SNIPpet of the most recent ARRL
Letter. It discusses other CODEC licensing issues that the
amateur radio community is facing with respect to digital voice
systems. It seems D-Star, with the CODEC embedded in a chip, is
at lease useable (by purchasing the chip) whereas those CODECs
that have been implemented in software cannot be used at all (at
least until some sort of licensing arrangement can be obtained).

As the article states, it is important at this point for some
competent amateurs to design an open source CODEC that will
perform well in amateur HF as well as VHF/UHF applications.

Might be a good project for AMSAT or TAPR.

-Les, K0BAD


> ***************
> The ARRL Letter
> Vol. 27, No. 30
> August 1, 2008
> ***************
>
> IN THIS EDITION:

<SNIP>

> * + HF Digital Voice Programs Once Again Available for
Download

<SNIP>

> ==> HF DIGITAL VOICE PROGRAMS ONCE AGAIN AVAILABLE FOR
DOWNLOAD
>
> Citing codec (coding/decoding) licensing issues, three free
Windows
> programs for sound card-based HF digital voice were yanked
from their
> download site for a short time recently, surprising hams who
are
> interested in HF digital voice operation; several online
groups that
> supported the software were also closed for a short time.
>
> WinDRM, DRMDV and FDMDV, all written by Cesco Lanza, HB9TLK,
used a
> codec that was developed for the US Department of Defense and
NATO.
> Rights to various forms of the codec are held by several
companies.
> According to Gary Pearce, KN4AQ, the companies have "winked"
at ham
> radio use for several years, but a recent complaint caused the
programs
> to be pulled from the download site. "Lanza did a quick
rewrite to use
> an open-source codec, and now WinDRM and FDMDV are back,"
Pearce said.
> "DRMDV, an intermediate program between the other two, has
been
> abandoned. WinDRM could always use the open-source Speex
codec, but
> FDMDV users will need to download the new version."
>
> Pearce said these three programs all allow hams to transmit
and receive
> digital voice by connecting their PC sound card to an ordinary
SSB
> transceiver: "The result has been surprisingly high quality
audio, with
> virtually no noise -- sort of like listening to FM, but in the
narrow
> bandwidth of a sideband signal. WinDRM, the best sounding
program, uses
> 2.5 kHz of spectrum. FDMDV sounds a little rougher, but uses
only 1.1
> kHz of spectrum. They both use OFDM modulation, a set of
close-spaced
> carriers that are each modulated with a little bit of data to
add up to
> the final digital signal. The main problem with HF digital
voice is that
> it needs fairly strong signals. FDMDV works better with weaker
signals
> than WinDRM."
>
> Pearce said that none of the available open-source codecs work
as well
> as the old one: "MELP <http://en.wikipedia.org/wiki/MELP>, or
Mixed
> Excitation Linear Prediction, was designed specifically for
> high-quality, low data-rate voice communication. So the on-air
audio
> might suffer some with the new version. Digital voice users
have been
> waiting and hoping for someone to concentrate on developing a
codec
> optimized for ham radio use, but none has been forthcoming."
>
> FDMDV and WinDRM can both be downloaded from Jason Buchanan's,
N1SU, Web
> site <http://www.n1su.com/>.
>
> The AOR digital voice modems and D-STAR radios both use the
AMBE 2020
> vocoder, and are not affected by the coding changes; the AMBE
2020
> vocoder is a proprietary chip that is embedded in each unit.
>
> For more information on WinDRM, check out QST Editor Steve
Ford's,
> WB8IMY, article ["Life Could Be a DReaM," pages 38-40] in the
April 2007
> issue of QST.

<SNIP>