So as someone that doesnt know much about telephony I want to confirm that how I think codecs work is indeed how they work.
So I am using Obi200 set up via custom provisioning (obifirmware). It supports the following 4 codecs:
G711U - 64kbit/sec
G711A - 64kbit/sec
G729 - 8kbit/sec
G726R32 - 32kbit/sec
iLBC - configurable 13kbit/sec or 15kbit/sec
Now here come the questions:
1) Am I understanding correctly that the codec encodes the data between me and google voice service. And so from the standpoint of compatibility with people calling me it shouldnt matter. As in, my choice of codec is not going to somehow make it so that I cant hear people calling me. Right?
2) Higher bitrate is not always better, 711 has been around since 1972 at 64kbits we can probably squeeze better sounding audio into 32kbit audio with modern advancements? So kbits is probably not a good metric?
3) I found samples for 711 here - http://www.en.voipforo.com/audio/g711-ulaw-25s.wav
unfortunately I cant find samples for others. But from reading about iLBC (googles codec now) is maybe a better choice? This kind of goes back to Question #1. Can I experiment/change codecs willy nilly without worrying about calls not working properly? Its just audio quality will change but calls should still be fine right?
EDIT - Found samples for all of the codecs. I uploaded them here http://www.mediafire.com/file/rkd307sa0kumlr4/Obi200_CodecSamples.zip
from listening to them, they sound very very close. I think using 1/4 of the bandwidth plus a huge bonus of being able to recover from packet loss iLBC would be a good way to go. But the more Im reading the more I am starting to think Google Voice doesnt support anything except G711U :(
4) This is what Google Voice supports:
PCMA - Im guessing this is 711A??
PCMU - And this is 711U??
G.722 - not an option for me right?
GSM - Not an option either?
iLBC
Speex - not an option either?
So does that mean that I cant use G729 or G726R32 ?
Also, are those current? Because the same doc that lists them also talks about XMPP, did SIP changeover change these (add/remove any?) https://developers.google.com/talk/open_communications
5) Does the phone being plugged into Obi via RJ11 have to worry about codecs? Or does that just get some standard PCM stream regardless of the codec picked because codec is only used between Obi200 and Google Voice server?
Thanks!
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