ADPCM - vs - G.726

[Steve Underwood <steveu (at) coppice.org>]

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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