T-Mobile has been supporting mobile HDVoice for over a year. However, my sense is that not very many people are actually experiencing HDVoice. If they are, they might not even know it.
For example, two of my associates have the Google/LG Nexus 5 handsets on T-Mobile’s network. Both are the sort of people who would hear and appreciate the difference that HDVoice makes. That said, both were initially of the impression that the Nexus 5 did not support HDVoice on T-Mobile!
This gave rise to the idea that we should devise a simple way to verify that a call was in HDVoice. If convenient, this would allow anyone interested to make a call between two handsets and know with certainty that the devices and call path was actually delivering HDVoice.
Devising such a test turns out to be very easy in a world of smart phones. All you need is a tone generator or a recording of a specific continuous tone.
Traditional narrowband calls a la PSTN standards are bandwidth constrained to pass only 300 Hz- 3.4 Khz. In contrast, wideband calls pass 50 Hz – 7 KHz. Therefore, a 5 KHz continuous tone can be heard across an HDVoice call, but not heard at all over a narrowband call.
A 5 KHz tone is easily generated using a freeware tools like JJ. Bunn’s AudioTool for Android, an app that I quite like, although there are numerous such apps available. A tool that created a tonal sweep from < 3KHz to > 5 KHz could also be useful in demonstrating the loss of tone across the upper boundary of a narrowband call path.
I recently used this simple test to verify that the Nexus 5 is HDVoice-capable on T-Mobile’s network. I took my wife’s N5 into one of the nearby T-Mobile stores and made a call from it to another Nexus 5. I then used my Nexus 4 to generate a 5 kHz tone in front of one of the Nexus 5’s. That tone was clearly and rather annoyingly heard coming from the other Nexus 5. This test works well enough even when using the speakerphone mode of the Nexus 5.
I didn’t want to try the patience of the store staff so I didn’t try making calls from the Nexus 5 to many other handsets while on-site. That said, I know for certain that calls from the Nexus 5 to my older (getting sad now) Nexus 4 do not pass the test tone, so are not HDVoice enabled.
In truth this little test would work for any two phones you care to try, even wireline desk phones. The simple fact that a smart phone app can be used as a reasonably precise tone generator makes the test conveniently portable, and a handy way to annoy the mobile carriers retails staff.
The more adventurous among you may wish to test further, trying various Bluetooth headsets to see if they fit into a mobile HDVoice ecosystem. I may yet try that…another day, once the ringing in my ears has passed.