| 摘要 |
A system for digital conferencing over narrowband channels which allows use bymultiple simultaneous speakers and which allow for interfacing between vocoders which operate at different bit rates. The system takes advantage of the properties of multi-rate parametric vocoders (which includes the Sinusoidal Transform Coder and the Multi-Band Excitation Vocoder, as well as embedded coders), defined as parametric vocoders for whom the basic model and parameter set remain unchanged over a wide range of bit-rates. The system performs signal summation. To maintain quality for a single speaker while allowing multiple speakers, the system adaptively allocates channel bandwidth based on the number of speakers to be represented. This system also provides digital-to-digital conversion between narrow-band digitizers (vocoders) operating at different bit-rates. The system takes advantage of the characteristics of a particular class of coders, sine-wave based coders, which perform parameter estimation by sine-wave summation. Digital-to-digital conversion is performed by estimating the parameter set associated with the lower bit-rate digitizer from the parameter set associated with the higher bit-rate.
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