Mobile HDVoice; A Post In Three Acts

Act 1: The Future – Sprint To Offer HDVoice Nationwide in July

Sprint,  the nation’s number #3 mobile carrier, has announced nationwide rollout of HDVoice in early July. At present they have just a few test markets HDVoice enabled. While some met the announcement with enthusiasm, HDVoice observer Doug Mohney has taken a justifiable wait-and-see approach to this news as Sprint has made such promises more than once in recent years.

Ever curious, I thought it worth looking into what kind of HD Voice-capable devices they would be offering. The list of twenty handsets seems quite comprehensive. That bodes well for customers someday actually getting to experience HDVoice.

Just as significantly, the HD Voice capable handsets was easy to identify. The company lists “HD Voice” as a key feature that can be used to search through the entirety of their handset offering. Thus new customers can easily reference this feature while in the process of selecting their new handset.

That brings me to…

Act 2: The Present – T-Mobile Support for HDVoice One Year Later

It’s been some time since I bothered trying to get T-Mobile to reveal anything further about their support for HDVoice. You may recall that it was their big announcement of CES213. Since that time they’ve had basically nothing to say about it.

At the time of the announcement they offered a very short list of supported handsets, along with the promise that the list would be updated as new hardware was offered. That list was eventually abandoned and is no longer available.

At the present time if you want to know if any T-Mobile handset is HDVoice-capable you must visit the support section of their web site. There you will find a page for every phone that they offer. In the “Tech Specs” for each handset you can find a status for “HDVoice capable” indicating Yes or No.

For example, the following image is a composite of parts of the page on the Nexus 5. It clearly indicates that the Nexus 5 is HDVoice capable.

This information is basically hidden from customers. If you don’t know what you’re looking for there is no way that you’re going to find it! There is certainly no practical way for a new customer to choose between handsets  using HDVoice as part of their selection criteria.

Even now, over a year later, Google searches for “T-Mobile and HDVoice” return little or no actionable information. The results returned are merely are the marketing blurbs about how great HDVoice sounds, and links to support forum posts where existing customers, including myself, have inquired about HDVoice.

Very clearly, for T-Mobile, the matter of HDVoice was purely a ploy for a moment’s attention at CES2103. Also, their web presence is a study in inconsistency, where a focus on the visual presentation renders any real, useful information very difficult to find.

In this instance, the uncarrier is uncommunicative, or at least uncooperative.

Act 3: The Past – A Misleading Nexus 5 Review

When T-Mobile launched their oh-so-mired-in-marketecture-but-not-so-burdened-by-facts HDVoice service I futilely sought to determine if my Nexus 4 was going to make the list of supported devices. It was the Android flagship at the time.

Later, when my wife’s Nexus 4 failed she purchased a Nexus 5, which prompted me to again look at whether we might be able to take advantage of HDVoice. This time the hunt lead me to what appears to be some bad information over at www.anandtech.com.

Yes, over at www.anandtech.com you can find a December 2013 review of the Nexus 5 by Brian Klug. That review makes specific mention of HDVoice support on T-Mobile as follows:

“I’m actually very impressed with how well the Nexus 5 performed at rejecting noise using the normal babble distractor track I use. In addition this was a T-Mobile AMR-WB “HD Voice” call between two Nexus 5s, illustrating that the Nexus 5 is indeed in the T-Mobile whitelist for HD Voice.”

…and…

“As an aside, the Nexus 4 oddly enough still hasn’t been green lit for HD Voice on T-Mobile, and given its age probably never will at this point, although the hardware is entirely capable.”

Of particular interest was the use of the term “whitelist” as a carriers means of enabling HDVoice. It had always been my impression that the carrier was required to do something to enable HDVoice for particular hardware, even if that hardware was BYOD. BYOD was T-Mobile’s earlier look-at-me-I’m-different horn-blast, from a time before they had access to the iPhone.

David Frankel, the CEO of ZipDX, who certainly knows a thing or two about HDVoice, now carries a Nexus 5 on T-Mobile. So does one of his close associates. He told me that he didn’t think that he was hearing wideband audio on his Nexus 5. This even though T-Mobile’s web site is quite clear on the matter.

Brian Klug supported his review with an audio recording intended to both be an example of the audio quality of the handset and profile its background noise reduction capabilities. In addition to the sample audio he included a screen capture of a spectrum measurement created using Spek, a freeware spectrogram tool. While the background noise reduction is, I think, indisputably good, the recording did not sound wideband to my ears. Further, I find that his interpretation of the Spek image is questionable.

I’ve long used Adobe Audition to take such measurements. Early on I learned that the display configuration needs to be tweaked to ensure that noise in the recording doesn’t appear as voice energy in the spectrogram image. Audition allows the user to calibrate the display where Spek does not.

I expect that what Brian saw as energy beyond 4KHz is simply noise. To prove this to myself, and you also, I’ve created a little comparison. I took the sample audio from Brian’s review and converted it to 16 KHz sample rate. This is consistent with an HDVoice call, but allows Spek to use the full; vertical height of its window to create the spectrogram image. I then compared that to a known HDVoice file recorded on my Polycom VVX-600.

The image shown is much smaller than the 1920×1080 pixel original. The difference is quite clear. The audio that accompanies the Nexus 5 review (pictured left) has no voice energy above 4 KHz. The faint purple color above 4 KHz is merely the noise floor of the recording.

In contrast, the recording made using the Polycom desk phone (pictured right) has pronounced voice energy all the way to the 8 KHz top of the vertical scale. This is a textbook comparison of narrowband vs. wideband.

In addition, there is a brief period before the audio starts at the beginning of the wideband spectrogram image. You can see that there is some purple tinge to that area. That too is just the noise floor. The presence of noise reflects the capability of the measurement process, not the presence of wideband audio in the recording.

Given this comparison I think that Mr. Klug merely misinterpreted what he was seeing in Spek. This calls into question his assertion that the Nexus 5 supports HD Voice when used on T-Mobile’s network. That is a question that I intend to answer definitively in a future post.