[Asterisk-Users] ADPCM - vs - G.726

[Whisker, Peter]

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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