HD telephony
HD telephony (also known as High Definition Sound Performance or HDSP , a Gigaset trademark ) is making calls with high voice quality . With the G.722 codec used for this , a larger part of the natural frequency spectrum is transmitted than with conventional telephony using G.711 .
For HD telephony to work, the entire chain between the telephones involved must be HD-compatible.
history
While in the early days of telephone service there was only an analogue transmission of the voice signal via copper wire pairs , telephony is now mainly digitally switched and processed.
The signals of an analog transmission channel when telephoning are limited to 3400 Hz by means of a low-pass filter . This limitation of the bandwidth is an essential prerequisite for the multiple use of telephone lines by means of carrier frequency technology , the operation of directional radio links and for the construction, as well as the efficient operation of long-distance telephone lines including repeater offices . This limitation of the bandwidth of the transmission channel results in a slightly dull sound. So that the conversation partner does not have the impression of being stuck on a dead line, a certain amount of noise is generated even when there is silence. The echo compensation allows a certain amount of noise to pass through and provides the typical telephone sound.
With the digitization of switching technology using ISDN at the end of the 1980s , telephone calls were no longer transmitted by galvanic switching and signal regeneration, but instead digitized in the exchange or converted back into an analog signal. In addition, the possibility of direct digital data existed with the central office exchange by used an ISDN connection.
The ISDN specification provides for 64 kbit / s per channel. A normal ISDN connection has two channels ( basic connection ) or 30 channels ( primary rate connection ).
The switching technology basically transports this data bit-transparent , i. H. without conversions. The bits sent correspond exactly to the bits received. However, data can be marked as language. In this case, data could also be converted. G.711 was specified as the codec in Europe. This requires exactly 64 kbit / s and covers the frequency spectrum from 300 Hz to 3400 Hz. In Europe, A-law is used , in the USA and Japan, µ-Law is preferred . Furthermore, a broadband voice service “7 kHz audio-coding within 64 kbit / s”, based on the G.722 codec, was introduced with the digitization of the telephone network in ISDN. In ISDN, however, there was not a significant number of devices that supported this codec. This was mainly used by radio stations that transmitted reports between a corresponding device and the studio technology via G.722 in the broadband voice service.
requirements
It was not until the introduction of IP telephony (VoIP), the transport of voice data over IP networks, that the G.722 codec was rediscovered. This is mainly due to the expired patents, the codec can now be used without a license.
In order to be able to use HD telephony, it is therefore necessary to use VoIP or special devices that support HD telephony. The coupling of two Fritz! Box models via ISDN also supports HD telephony. However, the data must be transmitted bit-transparently, which is not the case with the "fake" ISDN connections of many small providers. In addition, the data must not be converted by the network, as this would violate the bit transparency.
The language transmission standards Linear PCM 16 and PCMA 16 with 16 kHz sampling rate and a frequency spectrum from 50 Hz to 7000 Hz are used. The natural sound spectrum of a conversation, which ranges from 20 Hz to around 8000 Hz, can be transmitted better. Fixed line telephone calls to date have transmitted frequencies between 300 Hz and 3400 Hz, i.e. less than half of the possible spectrum. In practice this means that up to now, especially the higher and lower tones have not been transmitted.
A new function is the speech pause detection. In this way, no data is to be transmitted during periods of silence, only the information that there is currently no noise. As a result, an HD call sometimes sounds as if it was broken off. This function can also be switched off.
To avoid incompatibilities, most phones support a ranking list of the codecs to be used. If G.722 is not mentioned first, it will not be used even if both remote stations and all switching and conversion devices in between would support the codec.
As of August 2013, calls in HD quality between different networks (e.g. landline to cellular network) or between different cellular network operators are generally not possible. The reason is that there are no gateways between the systems and networks.
Telephony service provider
The telephony service provider must also support HD telephony. In the case of independent operators such as sipgate , the telephone call is, if possible, handled directly between the participants. This is then not a problem.
However, if the call is only accepted by a media gateway , it must accept G.722 data. In addition, the recipient must be in the same network or there must be an exchange with a gateway from another service provider that can also process G.722 data, and this exchange must also be activated. Otherwise the call will not take place or other codecs will be used.
DECT
Also DECT phones support codec G.722. While the normal codec for DECT is G.726 ( ADPCM with 32 kbit / s), so-called HD telephones also support the G.722 codec and thus HD telephony. The corresponding base station must not be connected via an a / b connection, but must forward the data via ISDN (Fritz! Box) or VoIP (e.g. Gigaset bases with VoIP technology).
This extension of the original DECT standard is also known under CAT-iq .
Cellular networks and availability in Germany
In GSM - and UMTS -Mobilfunkstandard HD voice is available for several years. It was not supported by the network operators for a long time. A device with AMR-WB support is always required for use. This is marketed under the term HD Voice . For the technology used, see Adaptive Multi-Rate .
Deutsche Telekom was the first provider to introduce HD Voice within its UMTS network in November 2011. This was followed by Vodafone in July 2013, E-Plus in March 2014, and Telekom in October 2014 between mobile and NGN fixed networks. Telefónica Deutschland introduced HD-Voice with its brand O 2 in 2015 .
In the fixed network, HD Voice is available in the networks of O 2 , Vodafone and Deutsche Telekom.
| Cellular network | GSM | UMTS | Volte | Wi-Fi calling | From:
To: |
Telefónica | Telecom | Vodafone |
|---|---|---|---|---|---|---|---|---|
| Telefónica | Mostly | Yes | EVS | EVS | Telefónica | Yes | Yes | Yes |
| Telecom | Yes | Yes | EVS | EVS | Telecom | Yes | Yes | ? |
| Vodafone | Yes | Yes | EVS | EVS | Vodafone | Yes | ? | Yes |
|
Status: August 2018
|
||||||||
Enhanced Voice Services (EVS, HD Voice Plus)
Compared to AMR-WB, EVS offers an audio bandwidth of up to 20 kHz. EVS is supported via VoLTE and Wi-Fi calling in the cellular networks of Telefónica, Telekom and Vodafone. However, a corresponding terminal is required for this.
| Manufacturer | model |
|---|---|
| Pixel 3 | |
| Pixel 3 XL | |
| Apple | iPhone 8 and newer |
| Huawei | Mate 20 Pro |
| Huawei | P10 |
| Huawei | P20 |
| Huawei | P20 Pro |
| LG Electronics | G7 |
| Samsung | SM-G930F "Galaxy S7" |
| Samsung | SM-G935F "Galaxy S7 edge" |
| Samsung | SM-G950F "Galaxy S8" |
| Samsung | SM-G955F "Galaxy S8 +" |
| Samsung | SM-G960F "Galaxy S9" |
| Samsung | SM-G965F "Galaxy S9 +" |
| Samsung | SM-N950F "Galaxy Note 8" |
| Samsung | SM-N960F "Galaxy Note 9" |
| Sony | F8331 "Xperia XZ" |
| Sony | G8341 "Xperia XZ1" |
| Sony | H8216 "Xperia XZ2" |
| Sony | H8314 "Xperia XZ2 Compact" |
| Sony | H8416 "Xperia XZ3" |
Problems
The AMR-WB Codec G.722.2, which is optimized for mobile communications but requires a license, has established itself in mobile communications, while landline and VoIP devices support almost only the license-free G.722 codec. Telephony in the LTE network (VoLTE) will also support HD telephony via AMR-WB. So far there are hardly any end devices that support AMR-WB and G.722 at the same time. The VoIP clients integrated in many Symbian devices from Nokia support e.g. B. mostly AMR-WB, but no G.722, while most VoIP devices (e.g. Gigaset IP, Fritz! Box ) support G.722, but no AMR-WB. A direct HD conversation between these devices can therefore only take place via suitable gateways of the network operators who carry out the necessary transcoding. This has already been implemented in the gateway from Telekom Mobilfunk to Telekom NGN Fixed Net.
Individual evidence
- ↑ PageHDSPSound ( Memento of the original from December 20, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Daniel Behrens: Telephoning in HiFi Quality - Tips & Backgrounds. In: pcwelt.de. July 1, 2009, accessed June 14, 2013 .
- ↑ Requirements for HD telephony. (No longer available online.) In: AVM knowledge database. April 10, 2013, archived from the original on June 2, 2013 ; Retrieved June 14, 2013 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ a b HD Voice for the UMTS network from Vodafone. In: heise.de . July 29, 2013, accessed March 8, 2015 .
- ↑ Telekom customers make calls in HD quality. (No longer available online.) Telekom, November 2, 2011, archived from the original on November 1, 2014 ; Accessed March 8, 2015 (press release). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Magnus Kleditzsch: Vodafone increases voice quality in the mobile network. In: Vodafone Blog. July 25, 2013, accessed March 8, 2015 .
- ↑ Brilliant sound: E-Plus launches HD Voice. (No longer available online.) E-Plus, March 12, 2014, archived from the original on November 1, 2014 ; Accessed March 8, 2015 (press release). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ HD Voice is now possible between the cellular network and the fixed network connections. In: Telekom Profi news. October 1, 2014, accessed December 30, 2018 .
- ↑ Markus Weidner: Introduction at o2: HD Voice in future in all German networks. In: Teltarif.de . March 7, 2015, accessed March 8, 2015 .
- ↑ Markus Weidner: Report: In future, significantly better voice quality with o2. In: teltarif.de. July 4, 2018, accessed December 30, 2018 .
- ↑ a b https://blog.telefonica.de/2018/08/enhanced-voice-services-brillantes-hoervergnuegen-im-lte-netz-von-o2/
- ↑ a b https://blog.telefonica.de/2017/09/hervorragende-sprachqualitaet-ueber-netzgrenzen-hinweg-mobilfunkkunden-nutzen-hd-voice-fuer-telefonate- between- telefonica-und-der-deutschen- telekom /
- ↑ a b https://blog.telefonica.de/2017/12/telefonate-in-ausgezeicher-sprachqualitaet-telefonica-kunden-telefonieren-jetzt-mit-hd-voice-ins-vodafone-netz/
- ↑ https://www.telekom.com/de/medien/medieninformationen/detail/brillantes-klangerlebnis-mit-hd-voice-plus-494308
- ↑ Markus Weidner: Vodafone starts HD Voice via GSM. In: teltarif.de. October 26, 2016, accessed December 30, 2018 .
