On 03/06/2012 08:00, Steve Underwood wrote:
>> I Googled "Iridium Codec" and this came up:
>>
>> DVSI AMBE-2020™
>>
>> www.dvsinc.com/products/a2020.htmCached - Similar
>> You +1'd this publicly. UndoThe AMBE-2020™ Vocoder Chip is a low cost,
>> DSP-based voice codec for ... Satellite systems such as Iridium, ICO,
>> Inmarsat, Thuraya, ACeS, Optus and ...
> They must have changed, or at least provided more options. It seems
> several systems which started out with other codecs later changed to
> AMBE, or made it an option. In the case of Inmarsat and Iridium I
> suspect that may be for reasons of interworking with terrestrial
> emergency services, which all went with AMBE. At these bit rates you
> *really* don't want the quality loss that ensues from a transcode.
yes, I think there is little doubt that DVSI have done nearly all of the
codecs of anything of interest in "low bandwidth" in the last 10+
years. I'm reasonably sure that DVSI did the Iridium codec, but not
clear on the exact details, 2,400+FEC fits with what we know of the
actual system capabilities. If anyone really cares I can actually go ask
Iridium and Inmarsat for all the details, but I think we probably know
enough now to move on - it's of cursory interest to know the exact
details of someone else's system?
However, I haven't yet tried cascading Codec2 to satellite - this is one
of my interesting use cases so I will try shortly - however, I'm
expecting it to be rather poor..?
Oh, finally has everyone spotted this:
http://www.opus-codec.org/
It's not 100% clear what it really is, but it states that it's a
derivative of Skype SILK codec and Xiph's CELT codec. The benchmarks
all focus on the 64Kbit range and compare against stuff like AAC.
However, it claims to work down to 6kbit and offer automatic "music" or
"voice" implementations (might be of interest given the recent discussions?)
Ed W
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