High-definition telephony, also known as HD Voice, is an audio standard that allows classic cell phone calls to be made with significantly higher sound quality. The voices of both interlocutors can be heard more clearly and naturally, which improves the understanding between each other. It is also practical to automatically mask annoying background noise with the help of a special compression process.
HD Voice from an artistic point of view
HD telephony is implemented in the frequency range between 50 and 7000 Hz, classic telephone communications without high-resolution voice transmission in the range between 300 and 3400 Hz. If you take into account the fact that human speech occurs in the 50-12000Hz range, then these numbers alone make it clear that the audio picture with HD Voice should sound more natural.
Technically, the AMR-WB audio codec is used for high-fidelity communication in mobile communications and the high-fidelity audio communication is usually implemented over the mobile networks of the three German mobile network operators. Basically, the audio is recorded in HD phone calls first, then numbered in the next step and then transmitted to the conversation partner in a compressed but qualitatively improved manner.
Free HD telephony is activated in the cellular networks of O2, Vodafone and Deutsche Telekom. However, one of the requirements must be met in order to be able to use the language standard at all. The cell phone used personally must support HD voice communication. However, since Apple is using this standard from iPhone 5 and Samsung from Galaxy S3, most of them should be able to use HD Voice. In other words: Only those who make calls with a very old smartphone model cannot use HD Voice. These are often those telephones that do not support LTE and should be replaced anyway.
With LTE, you should also check whether your smartphone supports Voice over LTE (VoLTE) and whether it has been activated in the mobile phone. Here the call quality is also better than the classic GSM connection. Create a faster connection, too. However, in principle, HD Voice is also possible in the GSM network, provided that the cell phone supports it.
HD Voice Plus: Better sound quality thanks to LTE technology
Meanwhile, all three network operators have introduced and launched an upgraded version of HD Voice. HD Voice Plus should offer the same benefits as the already known audio standard. Additionally, improvements have been made to the overall quality of service. Network operators assure that the technology can only be used in the LTE network, and thanks to the so-called Enhanced Voice Services (EVS) codec, it guarantees a higher frequency range of up to 20,000 Hz. So far only up to 7000 Hz has been possible. HD Voice Plus has been available on the Telekom network since May 2017. In Vodafone Germany, this technology is called Crystal Clear and has been in operation since May 2016. Telefónica talks directly about the EVS standard.
HD Voice Plus should improve the sound quality further and be more robust against transmission errors and signal fluctuations. Overall, the technology promises a more natural sound experience. Discussions between service providers should also be possible.
VoLTE: Network operators work together
For a long time, high-quality phone calls in the cellular network had an advantage: network operators could only offer VoLTE within their own network. The problem is obvious: when you call someone you are not referring to their network operator. Network operators are now working on this issue and providing interfaces through which VoLTE calls can be made over networks.
HD Voice also works in a fixed network – but by no means among all providers
By the way: HD Voice can also be used for free on Deutsche Telekom landline network. To do this, both ends of the call must use an IP-based connection from Telekom and HD Voice from terminals that support the G.722 encoding standard. This is also the case now with Telefónica: calls between users from LTE and fixed IP network via HD Voice are also supported. In some cases, it is also possible to make calls over networks in HD quality, for example between Telekom and Vodafone Kabel. Essentially, however, networks must be interconnected for cross-network communications.
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