On 31/05/2012 23:24, Robert Staton wrote:
I believe Inmarsat has more than one type of phone, with different
codecs at different rates. I have an Inmarsat Pro phone, and the
bitrate is 2.4kbps. I think the older phones use a higher bitrate.
See I'm not so sure on that..? Certainly the data pipe is 2,400
effective, but that doesn't mean it's the same used for voice
For example my uncertainty on the Iridium is that they have nearly a
3.5Kbit connection to the satellite, but they use a ton of FEC and frame
packing on the data connection giving you the effective 2,400 pipe for
user data. However, on the voice channel they may well use a different
encoding. Some very brief notes in the sidebar here (google the numbers
to get the source):
http://www.mailasail.com/Support/Iridium-Bandwidth
I believe the Fleetbroadband (FBB) and ISatphone pro use the same voice
codec? The FBB has quite variable voice quality depending on whether
you have the antenna static or rolling around on a boat. Static quality
is extremely high - I would say competitive with cellular and so perhaps
equiv to G723.1. However, it degrades reasonably under stress and
sounds more like Iridium, however, I have no idea what level of error
correction and loss of bandwidth that actually means in practice -
certainly it's not doing a skype like loss concealment, it just
continues at lower quality...
It seems hard to believe that the ISatphone Pro is using only 2.4kbit,
but if so then it would very much be a benchmark to emulate...
Note I haven't heard dstar quality to compare
Should we propose a standard paragraph of speech to have a similarity on
bunch of voice samples?
Ed W
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