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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  • Wolfpup - Thursday, April 5, 2012 - link

    For YEARS now I've been annoyed that while they keep piling on new features, cell phone voice quality remains atrocious. I used to think land lines sounded horrible...but now by comparison they're almost like you're standing next to someone.

    So cool that someone's doing this, and it would be cool if it ends up a competitive advantage for Sprint (hey, remember the "pin drop" commercials?)

    Current call quality is so terrible that doubling the bit rate would be a massive upgrade.
  • dubyadubya - Thursday, April 5, 2012 - link

    Not sure where you live but LL quality has been the voice quality bench mark forever. I would guess you or the people you talk to have crap phones. Most phones are crap these days. About a year ago needed a new home phone system. I ended up buying and returning 3 sets before finding something I could live with. The best sounding phones ever made were old Bell phones and they were tough as nails.
  • A5 - Thursday, April 5, 2012 - link

    LL service isn't exactly high quality either, it is just more consistent. 8-bit, 8 Khz sampling isn't really ever going to sound good.
  • jhlundin - Thursday, April 5, 2012 - link

    I completely agree with the poor quality of cellular audio... I upgraded my VoIP from the G.729 codec to the G.711 codec which is the standard for PSTN and updated my wireless around my home and office to the 1.9ghz DECT... and that made a real difference for *all* my calls... Why can't everybody just add the G.722 codec to move their cellphone into the bottom end of the "wideband" arena and improve the quality (I notice that there are a number of Android VoIP apps that support G.722 for under $10)...?
  • philpoe - Thursday, April 5, 2012 - link

    It looks like from the article that phones with 2 mics that can do common mode voice rejection, when paired up with a CDMA 1x-Advanced network, and EVRC-NW codec will be capable of HD voice. That sounds like a software update, and hopefully from Sprint instead of the handset manufacturer.

    Does that boil down to Sprint-to-Sprint calls on advanced smartphones get HD Voice?
  • NoelRoscoe1 - Thursday, April 5, 2012 - link

    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

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