On Fri, Mar 21, 2008 at 04:23:00PM -0500, Rick Parrish wrote:
> Jeff Brower wrote:
> >All the standardized codecs that I know of, both ones with IP rights
> >requirements and free ones, provide a reference design, typically
> >fixed-point C code plus test vectors. I wonder why DVSI has not done
> >the same.
>
> Perhaps the APCO and TIA committees did not require it when the
> algorithm was published ten years ago.
I'm sure there was a bit of negotiation to get the best
available vocoder technology and still preserve MIT's and DVSI's
interests. A full reference implementation in C would have been
immediately employed by a variety of entities seeking to use the
technology without the royalties and control DVSI and MIT wanted -
anything published like that would have been impossible to control.
And history indicates they made a choice that served their
interests well - radio hobby and hacker and far east clone (read
"Chinese copy") use of P25 IMBE on a PC or in unlicensed hardware has
not been a major issue for 10 years, though no doubt more than a few
versions do exist outside of official DVSI licensees. It is hard to
believe this would have been true if the standard came with C source
code... regardless of its license status and the formal restrictions on
using it.
And this has no doubt made it easier to collect revenue from the
hefty fees for licenses... if only because at least some major users
haven't been as annoyed by hobby software that scares their law
enforcement customers away from P25 + IMBE as they no doubt would have
been if unofficial copies of the C from the standard were available and
in wide use in PC radio hobby software. It is at least probably true
that at least two common VHF/UHF non P25 digital radio systems that
currently are not supported by readily purchased scanner would be
readily monitorable by the general public if IMBE source was available,
even with the potential patent infringement involved - and I am sure
this hasn't escaped notice.
--
Dave Emery N1PRE/AE, [EMAIL PROTECTED] DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."
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