The G.726 codec is the current Asterisk 1.2 version (revision 7221). I
am using G.711a (alaw) between a Sipura ATA and Asterisk at each end of
the link and am testing alternative codecs on an IAX link (not in trunk
mode) between the two Asterisk servers. (Yes, I know that the Sipura can
do G.726-32 also).
When I have G.726 switched in as the codec, it seems to add a little
gain as well as the clipping clicks. If I use G.711 on the
Asterisk-Asterisk link there is no problem. ADPCM seems to behave better
than G.726 but is percepibly "fuzzy".
GSM as I expected sounds like an old pre-EFR mobile phone. And the rest
are worse or like G.729 or Speex, eat processor power. I have G.723 and
G.729 compiled from the Intel distro.
Peter
Steve Underwood wrote:
Whisker, Peter wrote:
I have been looking at the medium-rate codecs in Asterisk - ADPCM and
G.726. Both of these are adaptive PCM codecs - the G.726 one is a little
more expensive in processing power, however both are 32k bit-rate.
I am experiencing problems using G.726 where the audio level is high. It
produces loud clicks as if clipping. For quiet audio however, it seems
fine.
ADPCM (Digilogic VOX?) seems to be better in this respect without the
clicks but has slight artifacts audible.
Anybody had the same problems with G.726? I can't find any comparisons
out there between the two codecs - does anyone have a link?
Thanks
Peter
If it does strange things at high volume the G.726 codec is buggy.
G.726 has a number of bells and whistles, such that DTMF and some
lower speed modems will pass through OK, and so tandem operation does
not become progressively worse. The OKI/Dialogic ADPCM doesn't have
these, and as a result cause far less CPU loading. However, for
typical speech only use they should offer comparable quality.
Regards,
Steve
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