On 01/06/2012 08:45, Ed W wrote:
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.
So some light digging suggests:
- Inmarsat Mini-M uses a 3.6Kbit AMBE codec with FEC bringing total up
to 4.8Kbit (older M might have been IMBE)
- Inmarsat FleetBroadband uses what they call 3.1Khz 4kbit AMBE+2
(definitely better quality than Mini-M to my ear)
- Inmarsat Isatphone Pro is not clear. Lots of blurb simply says 2.4Kbit
voice. Decent quality in practice, probably lower than FBB
- Iridium is not clear on codec. They certainly have data channels of a
touch under 3.5kbit before framing, and a user data channel is 2.4kbit +
FEC. I would guess that like the mini-M they use a 2.4Kbit+FEC AMBE codec.
I can go ask some engineers to confirm the above, but mainly I was
interested just so that I can use them as sensible benchmarks. No point
getting over excited about a comparison with vastly larger kbit
streams. From this it seems like Iridium and Isatphone Pro are sensible
benchmarks.
(I guess it's obvious to those who work in this business that DVSI
produced all the above (and quite a lot of the other low bandwidth
codecs in use). Seems like they are your go to for low bandwidth stuff)
I will look at recording some samples on different equipment and
combinations.
Ed W
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