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New Member

G726 for fax

I know we use G729 and G711 for fax in most cases. Can we actually use G726 with either relay or pass through?Here is the scenario. Thanks



Re: G726 for fax

we can add latency by changing the playout buffer size. Fax pass-through will be problematic (if it works at all) with


New Member

Re: G726 for fax


any codec which uses compression tehcniques (g729, g726, g723) is unsuitable for fax pass through as the tones representing each sample on the original bitmap from the fax needs to reach the other end of the connection exactly as sent, and the only codec cabable of this is g711.

You can configure g729 codec on ATA and IOS devices for voice calls and switch to G711 as needed (called upspeeding on some documentation) but that doesn't mean your faxes are being carried by a g729 codec which is in fact impossible because this codec works upon the fact that the human hear is incapable of interpeting all the frequencies on the audio spectrum which on a regular phone line are limited to the 4 khz upper range, but fax machines do use precise tones which are turned into garbage by lossy codecs like G.729.

Hope this helps.


New Member

Re: G726 for fax

Thanks. Actually I did verift the g729 upspeed to g711 and worked fine. What I am trying to ask now is that G726 should also be able to upspeed to g711 right?