The Case Against G.722

Posted on July 16, 2013 by

“Why don’t you support G.722?”

It’s a question we’ve heard more than once. People are very interested in G.722 wideband audio codec because voice communications can sound clearer.

There are several reasons Flowroute does not support G.722. Primarily, though, because we are an interface to the PSTN there is no benefit to us or to our customers by supporting G.722. I’ll explain why.

First, I want to provide the context for this reasoning by explaining the relationship between G.722, and G.711 and G.729 narrowband audio codecs used in digital voice transmission.

The frequency range of the human voice is roughly 80Hz to 14kHz. Audio transmitted over the telephone network is limited to frequencies between 300Hz and 3.4kHz, 4kHz including guard bands. In order to facilitate transmission of voice, phone systems compress voice audio to conform with the PSTN.

The telephone network carries G.711 and G.729 audio codecs, which were designed to deliver audio up to 4kHz. G.722 encodes audio at up to 8khz, which sounds great over VoIP networks that aren’t subject to compression and makes it easier for people to differentiate the sounds of certain consonants like ‘f’ and ‘s’. But once G.722 hits the PSTN, the frequencies encoded are cut down to the 4kHz range and quality is lost, rendering the audio inferior to that experienced with G.711 or even G.729.

So the big reason Flowroute does not support G.722 is that the traditional telephone network isn’t equipped to handle it. And once a call goes off net, there is no guarantee it won’t touch the PSTN, so quality cannot be guaranteed.

Until the PSTN catches up and supports 8khz audio end to end, G.722 will be transcoded out of G.722 and back during transmission. At each of those translation points, quality is damaged. Which is why Flowroute stays out of the audio path, to eliminate points of failure.

While it’s true that some carriers, like T-Mobile, are beginning to offer wideband service, narrowband codecs remain the standard. We’re in favor of supporting G.722 natively, where end-to-end wideband audio is possible. Otherwise, we’d have to get in the way of call audio and ultimately provide a lower quality audio going to the PSTN. And we’re not prepared to put the quality of your calls at risk by routing or accepting G.722 for calls where wideband audio is not supported.