Blog about voice enhancements

Always a wideband experience – Part 2

Always a wideband experience – Part 1

Today many mobile operators are upgrading their 3G networks to support crystal clear HD Voice calls. Just three weeks ago, GSA announced their 100th HD voice network deployment.

Part 1 - Figure 1 - Mobile HD Voice deployments

Figure 1: Global HD Voice deployments. Source: GSA

Some other operators are even one step ahead and are planning to deploy VoLTE over their 4G LTE networks in the course of 2014. HD Voice is a standard feature on VoLTE. HD speech quality is excellent when available, but the reality is that you end up with a traditional narrowband call more often than not. In a series of two articles, VoiceGurus will have a look at HD voice and the benefits of Bandwidth Extension technology. This article is part one, in which we will have a look at the market today. In part two, we will discuss how Bandwidth Extension technology enhances the quality of narrowband calls to bring back that wideband experience.

1. The difference between human conversation and a phone call

If you would analyze the frequency spectrum of a human voice, you’ll see that the bandwidth is approximately 12 kHz. However, most phone calls today are narrowband, meaning that the sampling frequency is 8 kHz. According to the Nyquist theorem this would allow a bandwidth of 4 kHz, but in real phone calls the spectrum runs from 200 Hz to 3.7 kHz. Although this might be sufficient in most cases for having an intelligible phone call, the sound is actually nowhere near the original voice. Compared to the original, voices sound quite muffled and the low frequencies of a deep male voice are gone. Figure 2 shows this difference in a spectrum plot.

Part 1 - Figure 2 - Full Band recording (NS OFF) NB WB spectrum PPTX

Figure 2: Spectrum of a male human voice and the bandwidth covered by narrowband and HD Voice

2. HD Voice is trying to close the gap

For this reason, many mobile network operators today are upgrading their 3G voice services to wideband, also known as HD Voice. Technically speaking, the sampling frequency is increased from 8 to 16 kHz. To offer an HD Voice service between two callers, all components in the communication chain need to be upgraded, both in the network as well as the mobile phones. If one of them is not supporting HD Voice, the service will fall back to a regular narrowband connection.

HD Voice increases the spectral bandwidth to a range from 50 Hz to 7.5 kHz. This makes voice calls sounding much more natural, i.e. much closer to the original voice. Today HD Voice is already available on many 3G networks and it will be a standard feature on 4G LTE networks once operators will start to offer Voice-over-LTE (VoLTE) services in the coming years. Figure 3 shows a prediction of the various HD Voice-capable mobile network standards in the coming years.

Part 1 - Figure 3 - Mobile network subscribers

Figure 3: Mobile subscriptions forecast per network standard. In 2017, 5.2 billion of the 8.4 billion mobile subscribers will be on an HD Voice-capable network. Source: Ericsson Mobility Report, Nov 2013

3. Still a narrowband call, for some reason

Already today many consumers are starting to appreciate the benefits of HD Voice. For those of you using a 3G network service offering HD Voice, you probably recognize the excitement when the call turns out to be HD Voice. Once you’ve had the experience, you start expecting it every time again. At that same time, you start noticing when the call happens to be narrowband for some reason, or even worse, when the quality drops to narrowband during the call. This happens for example when you or the other caller moves out of the 3G coverage area. In that case the network will decide to fall back to narrowband in order to keep the connection alive. In fact, this happens quite often and it’s likely to stay that way in the coming years. As you can see in Figure 3, even in 2017 only 60% of the mobile subscribers world-wide will have a wideband-capable connection and the probability of actually having a wideband call will be much lower. When available between two subscribers, HD Voice can be a very nice consumer proposition, but generally speaking it does not really deliver up to its promise in the coming years.

In part two of this series, we will discuss how Bandwidth Extension technology can help to strengthen the HD Voice value proposition for consumers.


Leave a Reply