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.
--- On Thu, 5/31/12, Ed W <[email protected]> wrote:
From: Ed W <[email protected]>
Subject: Re: [Freetel-codec2] Asterisk Feedback and tips
To: [email protected]
Date: Thursday, May 31, 2012, 3:19 PM
On 31/05/2012 19:25, Ed W wrote:
> Hi Folks
>
> Now that we kindly have an Asterisk codec provided, it's great for
> testing out voice quality.
...
> I setup prefixes so that I can dial:
> 40xxx dials the number using Codec2
> 41xxx dials the number using LPC10
> 42xxx dials the number using G732.1 5kbit
>
> This is great for comparing quality of codecs quickly.
I have tested using
- the asterisk echo test
- calling between two snom phones on g711
- calling between a DECT handset and a nokia wifi phone (g711 & ilbc)
- compared with Inmarsat/Iridium satellite (4/3 kbit ish each)
- Codec2 at 2,500 baud
My observation are:
- Codec2 is distinctly superior to LPC10. Both are a bit buzzy, but
LPC10 is distinctly more so. Voicing is somewhat similar with each though.
- Codec2 is substantially lower quality than 5kbit G723.1. Actually
quite amazing how good G723.1 is!! (6kbit G723.1 is MOS 3.9 !)
- Codec2 gives me a bit of earache after just a few mins. Not measured
it, but wondering if there is some harmonic distortion generated?
- Unsurprisingly multiple low quality codecs together are additively
poor. Dect + Codec2 has a noticable extra buzziness
- Quite a wide range of voice pitches are handled very nicely. I can
listen to my kids, wife and myself (British english speakers) without
any problems. Upper end of my kids and wife's voice goes distinctly
harsh and buzzy (guys talk in a falsetto to repro).
- Extremely understandable speech with that 8khz kinda feeling, ie not
nasally
- Codec2 deals quite badly with music on hold and ring tones. OK, even
GSM deals badly with music on hold, but the ring tones and other call
progress tones on the PSTN turn into farts and pops (amusing)
- Compared with Iridium/Inmarsat, those are both less buzzy and somewhat
easier to listen to
- Iridium I believe is somewhere between 2.4 and 3.4 Kbits (not clear
which). It is much more nasally sounding, but it's also smoother
sounding (less buzz). I believe they use a narrower freq filter range
(hence the nasally sound), but the vocoder is less buzzy, on the flip
side Iridium is less easy to hear the non plosive sounds and is often a
little "honky" compared with codec2. Overall codec2 is easier to
understand, iridium is smoother on the ear.
- Inmarsat is far superior to either and usually sounds extremely clear
when the signal is good, normally close to G723.1. However, it also
degrades very well with packet loss and sounds something like Iridium
under stress. I believe they use a 4+Kbit voice codec, but not sure
Overall seems very impressive. I guess I wish for a touch more voice
quality at the 2,400 level. What I mean by that is that it tends to
oscillate and "buzz" at pitches that are easily found in female and even
high voices - the actual voicing is great, satisfactory identification
of speaker from their voice, clear consonant sounds and non nasally
sounding - excellent. Kids voices are a tough challenge and codec2 does
an admirable job, not much worse than GSM, but I think probably the same
as above - higher pitched voices might be slightly falling outside of
the oscillator prediction area and tend to buzz a little too much?
(could the predictor follow the voice range?)
I haven't tested in the presence of significant background noise. Which
is to say I stood next to a noisy road and the tv, but it seems the
handsets I own or the input filters are killing the background noise
enough that it wasn't audible, nor a problem at the levels I tried. I'm
presuming this would be a tough challenge on any codec, but it seems
"normal" noise levels are no issue at all.
David, do you want to take a voice call over the PSTN using Codec2 just
for kicks? I'm on GMT, propose a time and tel number offlist if so. I
can also call on Iridium/Inmarsat
Thanks for your wonderful work!
Ed W
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