On 06/03/2012 02:58 AM, David Rowe wrote: > Steve - I doubt any Self/Codebook excited Linear Prediction type codec > (which I presume the SELP in PSELP stands for) could work at 2.4 kbit/s The named PSELP puzzled us from the time Iridium was first announced, for the reason you give. Even though I was at Motorola then, and doing speech work, I never saw the name expanded from its initials. Googling PSELP doesn't seem to bring up any hits at all. A lot of low bit rate military codecs have been based on some from of LPC, even as low as 1200bps. > > 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. > > - David > > On Sat, 2012-06-02 at 21:46 +0800, Steve Underwood wrote: >> On 06/02/2012 05:01 PM, Ed W wrote: >>> - 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 don't know if they changed, but the original spec for Iridium used a >> codec called PSELP at 2.4kbps. Iridium came from Motorola's defence >> group, and a lot of what they did reused things developed for the >> military. I believe PSELP was among those things. >> >> Steve >> Steve
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