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We humans have the ability to hear sounds in the range of 80 Hz to 14 kHz, which is pretty good considering the small size of the ears we were given. However, as we get older this range is reduced especially at the top end of the spectrum. The frequency band of normal human speech is much lower than this.

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Typically, the frequency for male speech ranges between 85 Hz to 180 Hz and for female it is between 165 Hz to 255 Hz. When we speak to someone on the phone the frequency reserved for the telephone call is in the range of 300 Hz to 3 kHz. This is just enough dynamic frequency to ensure the speech doesn't sound like it is coming from the moon or through an underwater pipe. 

 

Background and Codecs

All digital speech uses the concept of a codec. The word “codec” is an abbreviation combination of coder and decoder. This process describes the algorithm, which digitally encodes and compresses speech samples, so they can be transmitted to the receiver which then reverses the process. In a mobile network where the quality of the connection is changing continuously, adaptive codecs are used which can change dynamically depending on the network conditions. Let us say you start a call in a good coverage area, your phone may negotiate a high bit rate codec of 12.65kb/s. While on the same call you start driving your car to an area with high amounts of congestion, the network will instruct your phone to use a lower bit rate and lower quality call using perhaps 6.6 kbps, thus allowing more simultaneous calls to occur.

HD Voice

So what is HD Voice? It is represented as an improvement in the dynamic frequency of a voice call over and above that of a standard narrowband voice call. Technically this is known as AMR-WB (Adaptive Multirate - Wideband) which defines a number of bit rates and an improved sample rate, and algorithm complexity which when combined, increases the frequency response for the overall call.

If you have ever made a Skype to Skype call and have sufficient bandwidth, you will use the Skype Silk codec, which behaves like the industry standard AMR-WB codec, providing superior quality over and above a regular phone quality (although Skype will point out that their codec is better). Many IP telephony solutions such as Cisco’s Unified Communication Manager solution support wide band HD Audio, for on-net calls, so how much better is HD Voice over regular calls?

France Telecom conducted a survey in 2010 and of the sample group it found: 

  • 96% of customers are satisfied with HD Voice calls
  • 86% of testers say compatibility with HD Voice would be a selection criterion when purchasing a mobile in the future
  • 76% of testers would be prepared to change mobiles to obtain HD Voice


The above diagram shows the difference in dynamic frequency between a standard (NB) narrow band call and the improved HD Wide Band call.

Mobile Deployments

According to Global Mobile Suppliers Association, since the first service launch in 2009, HD Voice has been deployed on 41 mobile networks in 33 countries including: Armenia, Australia, Austria, Belgium, Bulgaria, Canada, Croatia, Czech Republic,  Denmark, Dominican Republic, Egypt, France, Germany,  Hong Kong, India,  Ireland,  Italy, Kenya, Luxembourg, Mauritius, Moldova,  The Netherlands,  Poland, Réunion, Romania, Russia, Serbia, Slovenia, Spain, Switzerland, Turkey, Uganda, UK.

Today, to benefit from the improved HD Voice for mobile, you need to be connected to an operator in one of the above countries and also have a compatible handset. Right now there are approximately, 73 compatible handsets including the Samsung Galaxy SIII, Nokia Lumia 900 and HTC One X. The Apple iPhone 4S doesn't support the standard, although the hardware is capable.

Limitations

Due to interoperability challenges, HD Voice is limited to calls originating and terminating on the same network. However, this will change over time as adoption and hardware support improves. Older networks will require an infrastructure upgrade to support the G.722.2 codec which is used by HD Voice.  If a HD Voice call terminates on the fixed line network, the resulting call quality will be low.  

LTE HD Voice

It is expected the AMR-WB codec family will play an important part for the development of LTE VoIP. Unlike HD Voice on 2G/3G, LTE VoIP is purely IP based and uses the SIP protocol. LTE network deployments are confined to densely populated areas, so handover to 2G/3G networks which support the AMR-WB codecs make it an obvious choice in this regard.  

By  Craig Sutherland

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