For a while now, a regular feature in our smartphone reviews has been comparison of smartphone voice quality on different devices, air interfaces, and codecs. Until recently, improving voice quality has been something of a secondary objective for wireless carriers, and improvements in voice codec efficiency has been used to increase total call capacity rather than improve cellular voice quality. 

Today however Sprint announced the introduction of its HD Voice initiative which will launch in conjunction with the HTC EVO 4G LTE. Our own Jason Inofuentes is at the event and will have impressions of the device soon, which is based around a 1.5 GHz MSM8960 dual core Krait SoC. For the HTC EVO 4G LTE, HD Voice consists of one part common mode noise rejection using two microphones (something we've seen ship on high-end smartphones for a while now), and one part 1x-Advanced.

Part of the CDMA 1x-Advanced specification is inclusion of support for higher quality EVRC voice encoding. At present, virtually all the CDMA2000 carriers in the USA use EVRC-B for their voice calls, which has adaptive bitrates of between 4 and 8 kbps and sampling of up to 8 KHz. Sprint has talked rather publicly in the past about upgrading its CDMA2000 1x network to 1x-Advanced, and that brings me to HD Voice.

I reached out to Qualcomm and asked what voice codec was being used in conjunction with Sprint's HD Voice branding on the HTC EVO 4G LTE, and learned that EVRC-NW (Service Option 73) is being used. EVRC-NW (Narrowband-Wideband), as the name suggests, includes both the EVRC-B rates with narrowband 8 KHz sampling, and EVRC-WB rates with 16 KHz sampling all under one umbrella.

The end result is double the frequency bandwidth for voice calls, and after Nyquist you get 50 Hz - 7 KHz  of frequency response. That's still a ways away from the widely cited 20 KHz upper bound for human auditory perception, but dramatically better than the present 50 Hz to 4 KHz of frequency range. In fact, 7 KHz of bandwidth should be sufficient to replicate human voice completely. EVRC-NW is superficially analogous to AMR-WB, and I've listened to a number of AMR-WB versus AMR-NB demos that are pretty compelling. Sprint moving on to wideband audio is definitely a welcome move here, and we look forward to testing it out. The only remaining question is just how aggressive and quick Sprint will be with its 1x to 1x-Advanced update. 

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  • fic2 - Wednesday, April 4, 2012 - link

    So, does this only do good for the person that I call with an HTC EVO 4G LTE? Seems like it wouldn't effect what I am able to hear. (As always I might be wrong.)
  • Solidstate89 - Wednesday, April 4, 2012 - link

    Unless they're using an "HD voice" compatible handset it does neither you or the person you're calling any good.
  • apinkel - Wednesday, April 4, 2012 - link

    The phone calling from and calling too both need to support it and the network in between must have been upgraded as well.

    I don't expect it to be something that's going to come into play for the avg user for quite a while but I like that sprint is moving in that direction and that their flagship phone supports it.
  • fic2 - Thursday, April 5, 2012 - link

    Thanks for the info.
    I would agree that it is good that Sprint is moving in that direction.
  • Solidstate89 - Wednesday, April 4, 2012 - link

    I must say, even though it's only compatible with the CDMA upgrade, the fact they're planning on rolling out this "HD Voice" feature over their 3G network is pretty nice. Verizon (and I assume AT&T) is trying to do the same thing but their implementation will ONLY be possible by using VoLTE. That this phone (and I'm assuming any future handsets to come on Sprint) will be able to use this HD voice over not only their upcoming LTE network, but also their CDMA network is pretty impressive.
  • mcnabney - Thursday, April 5, 2012 - link

    Yup, all I heard from this article is that Sprint isn't planning on moving to VoLTE anytime soon, which is really really bad. That means Sprint is commited to selling more of their infrastructure to raise funds and also not really interested in expanding LTE to cover their entire footprint like Verizon claims they will do by the end of next year. All this really means is that Sprint is choosing to make-do with old technology and provide the minimum service required. Fine, if you never leaves your suburban community, not so good if you ever go anywhere.
  • apinkel - Thursday, April 5, 2012 - link

    Sprint is moving CMDA into the 800 mhz spectrum as part of their network vision upgrades. That spectrum has better long distance propagation then the 1900mhz frequencies they are using for LTE so putting voice (the highest priority, lowest bandwidth) in CDMA makes a lot of sense for them.

    My understanding is that they don't have enough contiguous spectrum to deploy LTE at 800mhz.

    For most markets they should have good LTE coverage... similar to what their current cdma coverage at 1900mhz gives you today for voice.

    They do have areas where their spectrum holdings aren't as good... mostly in the southeast US... coverage may be more spotty in those areas.
  • xcharles718 - Friday, April 6, 2012 - link

    Currently, Sprint is in the process of ending iDEN services(which is on the 800MHz ESMR spectrum). Sprint plans to slowly thin out iDEN coverage and shut everything down in 2013. With the dropping iDEN subscribers over the years, some spectrum on 800MHz is opened up. It's not enough to deploy a 5x5 LTE setup(which they plan to do after iDEN is fully shutdown), but enough for 1 or 2 1x Advanced channels. This CDMA service would offer voice and 2G data. Both 1xA and LTE will co-exist on the 800MHz band after Network Vision is complete.
  • apinkel - Friday, April 6, 2012 - link

    Yup. Moving LTE into 800mhz requires advancements in LTE technology that aren't available today.

    One other thing to add... their initial LTE deployment will be in the 10 mhz (5x5) PCS G-Block. They have pretty much national coverage for this spectrum so their LTE coverage should be pretty extensive.
  • Penti - Saturday, April 7, 2012 - link

    Sweden and much of the rest of the world uses and supports LTE at 800MHz spectrum, the only real drawback is that there won't be any triple or quad-band LTE chipsets for terminals for many many years. The other is that we are waiting here for VoLTE and convergence with other technologies. For seamless and modern usage obviously. In Sweden they could employ pretty extensive service for 3G on 900-band for example. They really need to move to all IP-backbones and VOIP with VoLTE at the core in the background. Of course that in extension would make it possible to build even more extensive and flexible telephony services, you can also do voice over wifi and offer more extensive voip-services. Obviously upgrading infrastructure and services is a must, even if not all is here yet commercially. You can really on CDMA, GSM and 3G for voice for some more years, but using multiple radios instead of handover is a drawback. Doubling the sizes of batteries only goes so far.

    Deploying LTE on world mass consumer products is a bit of a hassle, there is no (significant at least) deployment of VoLTE and most basebands for the terminals are totally worthless and means a two physical baseband chips setup. They won't support whats deployed world wide, enough bands/frequencies as happened with the new iPad which don't offer any LTE service in most of the world. Baseband offers needs to mature, networks are really only fine for data use. Even when more power efficient and integrated baseband in terminals has reached the market it still won't be quad/triple band and would have to be configured for different frequencies/markets. No "world phones" for LTE just yet.

    UMTS operators has AMR-WB instead as the article points out. They aren't missing any.

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