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Concept
Téléphonie large-bande
Résumé
Wideband audio, also known as wideband voice or HD voice, is high definition voice quality for telephony audio, contrasted with standard digital telephony "toll quality". It extends the frequency range of audio signals transmitted over telephone lines, resulting in higher quality speech. The range of the human voice extends from 100 Hz to 17 kHz but traditional, voiceband or narrowband telephone calls limit audio frequencies to the range of 300 Hz to 3.4 kHz. Wideband audio relaxes the bandwidth limitation and transmits in the audio frequency range of 50 Hz to 7 kHz. In addition, some wideband codecs may use a higher audio bit depth of 16 bits to encode samples, also resulting in much better voice quality.
Wideband codecs have a typical sample rate of 16 kHz. For superwideband codecs the typical value is 32 kHz.
In 1987, the International Telecommunication Union (ITU) standardized a version of wideband audio known as G.722. Radio broadcasters began using G.722 over Integrated Services Digital Network (ISDN) to provide high-quality audio for remote broadcasts, such as commentary from sports venues. AMR-WB (G.722.2) was developed by Nokia and VoiceAge and it was first specified by 3GPP.
The traditional telephone network (PSTN) is generally limited to narrowband audio by the intrinsic nature of its transmission technology, TDM (time-division multiplexing), and by the analogue-to-digital converters used at the edge of the network, as well as the speakers, microphones and other elements in the endpoints themselves.
Wideband audio has been broadly deployed in conjunction with videoconferencing. Providers of this technology quickly discovered that despite the explicit emphasis on video transmission, the quality of the participant experience was significantly influenced by the fidelity of the associated audio signal.
Communications via Voice over Internet Protocol (VoIP) can readily employ wideband audio. When PC-to-PC calls are placed via VoIP services, such as Skype, and the participants use a high-quality headset, the resulting call quality can be noticeably superior to conventional PSTN calls.
Source officielle
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