Wideband audio

Among HD voice (also known as High Definition Sound Performance or HDSP, a trademark of Gigaset ) refers to the calls in high voice quality. In this case, a larger part of the spectrum is transmitted, as in conventional telephony.

This HD telephony works, the whole chain between the two telephones involved must be HD capable.

History

While taking place at the early days of the telephone service only analog transmission of the speech signal over copper pairs, telephony is nowadays mainly digitally mediated and processed.

The signals of a transmission channel on the phone are limited by a low-pass filter at 3400 Hz. This limitation of the bandwidth of the transmission channel to 3.4 kHz when making calls is an essential prerequisite for the multiple use of telephone lines by means of carrier frequency technology, the operation of radio links and for the construction, as well as the efficient operation of telephone trunk lines including amplifiers offices. By limiting the bandwidth of the transmission channel in a slightly muffled sound. Thus, the party does not have the impression that hang on a dead line, some noise is also generated during silence. The echo cancellation while still leaving a particular noise through and ensures the typical telephone sound.

With the digitalization of switching technology end of the 1980s/early 1990s (see also ISDN) telephone calls were no longer transmitted by galvanic through-connection and signal regeneration, but digitized in the exchange or remade into an analog signal (depending on direction). In addition, there was the ability to directly exchange digital data with the exchange, used by an ISDN connection.

Here, a specification was held at 64 kbit / s per channel. A common ISDN connection has two channels ( basic rate interface ) or 30 channels ( Primary Rate Interface ).

The switching technology transports these data basically bit transparent, that is, without conversions. The transmitted bits exactly match the received bits. However, there is the possibility to mark data as voice. In this case, data could also be converted. As this codec has been set in Europe G.711. This consumes exactly 64 kbit / s and covers the frequency range of 300 Hz to 3400 Hz in Europe is to A -Law, in the U.S. and Japan is preferably encoded by μ -Law. Furthermore, it was also a broadband voice service " 7 kHz audio -coding within 64 kbit / s", is introduced based on the G.722 codec with the digitization of the telephone network in the ISDN. In ISDN there was never, however, a significant number of devices that support this codec. This was therefore used only radio stations, the reports between a corresponding device and studio technology by the G.722 wideband transferred voice service.

Requirements

Was not until the introduction of Voice over IP, the transport of voice data over IP networks, the codec G.722 was rediscovered. This should mainly be due to the expired patents, the codec can be used today without a license.

To use HD voice, so is the use of VoIP or the use of special devices that support HD voice, required. The coupling of two Fritz! Box models via ISDN also supports HD voice. In this case, however, the data must be transferred bit-transparent, which is not the case with the " fake " ISDN connections of many small suppliers. In addition, the data may not be converted from the network (which would violate the bit-transparency ).

To use the voice transmission standards Linear PCM 16 and PCMA 16 with 16 kHz sampling rate and a frequency range of 50 Hz to 7000 Hz, the natural sound spectrum of a conversation that ranges from 20 Hz to about 8000 Hz, can be transmitted better. Previous landline telephone calls transmitted frequencies between 300 Hz and 3400 Hz, less than half of the possible spectrum. In practice, this means that so far particularly the higher and lower sounds have not been transferred.

A new feature is the silence detection. To ensure that no data is to be transferred, but only the information that is currently undergoing no noise at times of silence. This sounds a HD conversation at times as if it would be canceled. This function can also be switched off.

To avoid incompatibilities, most phones support a ranked list of codecs to be used. If G.722 not mentioned as the first, so it is even not used if both stations and everywhere in between switching and conversion facilities would support the codec.

As of August 2013, calls in HD quality between different networks (eg fixed to mobile ) or not between different mobile operators in general possible. The reason is not installed gateways between systems and networks.

Telephony operators

The telephony service provider must support HD voice also. For independent operators like sipgate the call is handled if possible directly between the participants. This then is not a problem

If the call but only accepted from a gateway, as this G.722 data must accept. In addition, the recipient must be in the same network or it must be an exchange with a gateway to another provider that can also handle G.722 data, and finally, this exchange must also be enabled. Otherwise, the call does not come about or have recourse to other codecs.

DECT

Also DECT phones support codec G.722. While the normal codec G.726 for DECT is (ADPCM at 32 kbit / s), support the so-called HD phones in addition to the G.722 codec and thus HD voice. The corresponding base station must not be connected via an a / b port, but must (eg Gigaset bases with VoIP technology ) to pass the data via ISDN ( Fritz! box) or VoIP.

It is known, this extension of the original DECT standard also CAT-iq.

Mobile network

In GSM and UMTS mobile phone standard to HD voice is available for several years. From the network operators but it was not supported for long. To use a terminal with AMR -WB support is needed in any case. This is marketed under the term HD Voice. To see the technology used Adaptive Multi-Rate.

Availability in Germany

• As the first provider to Deutsche Telekom HD Voice introduced in your UMTS network in November 2011.
• In April 2013, Vodafone started to network expansion in its UMTS network, this was completed in late July 2013.
• Since March 2014 HD Voice can also be used in the E-Plus network.

Although HD Voice in the GSM network would be possible, it is not currently offered by three providers.

Problems

The optimized for mobile, but licensed AMR -WB codec G.722.2 has prevailed in the mobile while landline and VoIP devices almost only support the license-free G.722 codec. Also telephony in LTE network VoLTE will support HD voice on AMR -WB. So far, there are few devices that support AMR-WB and G.722 simultaneously. The built- in many Nokia Symbian devices VOIP clients support for example mostly AMR -WB, but no G.722, while most VoIP devices (eg Gigaset IP, Fritz Box) G.722, but no AMR -WB support. A direct HD - talk between these devices could come about therefore possibly via suitable gateways of the network operator.