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Wideband audio, also known as 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 80 Hz to 14 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 or higher. ==History== 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. Some of the handsets manufactured by Nokia which run S60 and Series40 OS that support VoIP also support wideband audio.〔(Forum Nokia - VoIP details ).〕 A number of audio codecs have emerged to support these services, supplementing G.722. Manufacturers of audio conferencing equipment have introduced wideband-capable models that include support for G.722 over VoIP. Conference calls are a direct beneficiary of the enhancements offered by wideband audio. Participants often struggle to figure out who is talking, or to understand accented speakers. Misunderstandings are commonplace due primarily to generally poor audio quality and an accumulation of background noise. Some listener benefits cited of wideband audio compared to traditional (narrowband): * clearer overall sound quality * easier to recognize voices, distinguish confusing sounds and understand accented speakers * ease of deciphering words that have the close sounds of ‘s’ and ‘f’ and others, often indistinguishable over telephone lines * ability to hear faint talkers and to understand double-talk (when more than one person is speaking at the same time) * reduced listening effort (decreased cognitive load), resulting in increased productivity and lessened listener fatigue * better understanding in the face of other impairments, such as when talkers are using a speakerphone or in the presence of background noise Despite its reputation for poor audio quality, the mobile telephone industry has started to make some progress on wideband audio. The 3GPP standards group has designated G.722.2 as its wideband codec and calls it Advanced Multirate – Wideband (AMR-WB). A few handsets have been produced supporting this codec (for example, HTC, Nokia , Samsung and Sony, and network demonstrations have been conducted. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Wideband audio」の詳細全文を読む スポンサード リンク
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