Short for high-definition voice, and also called wideband voice, in Internet telephony, it refers to the use of wideband technology to provide a deeper clarity and better audio experience in VoIP communications. Traditional telephony is based on sampling the sound stream 8,000 times a second, and constraining the reproduction of the sound spectrum to the range between 200Hz on the low end to 3.3KHz on the high end-and fitting it into a 64Kbps bandwidth. In HD voice, a wideband codec doubles the sampling rate and more than doubles the width of the sound spectrum reproduced, from 50Hz to 7KHz. This adds significant depth and nuance to the transmitted sound-and it reduces the bandwidth requirement to 32Kbps, half that of PSTN transmission.
HD voice technology uses Digital Signal Processing (DSP) technology to capture and transmit the higher quality sound. Several wideband codecs currently being used for HD voice include G.722 and G.722.1, and the MPEG-4 AAC Low Delay codec.
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