| 单词 | voice band |
| 释义 | voice band The frequency band, or range, specified for voice communications in the public switched telephone network (PSTN).The total bandwidth of a voice grade channel is nominally 4 kHz. So, a single-channel voice grade circuit, supports a frequency band of 0–4,000 Hz. The bandwidth in the range 0–300 Hz generally is ignored, as the equipment is unable to deal those low frequencies. The voice band is approximately 3.0 kHz wide, running at 300–3,300 Hz. Signaling and control functions take place in the band 3,300–3,700 Hz.The lower band of 0–300 Hz and the upper band of 3,700–4,000 Hz are used as guard bands for maintaining separation between information channels, each of which is supported over a separate carrier frequency range, when analog voice channels are multiplexed using Frequency Division Multiplexing (FDM). See also analog, bandwidth, FDM, frequency, guard band, multiplexing, PSTN, and signaling and control. 74570c22.qxd 9/12/07 12:48 AM Page 525 |
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