Abstract: A terminal is disclosed for use with a system for digital conferencing over narrowband channels which allows use by multiple simultaneous speakers and which allow for interfacing between systems which operate at different bit rates. For each conferee, the terminals interconnect between an A/P converter and a modem, and contain an analyzer and a synthesizer. The analyzer receives digitized speech and encodes it at the system data rate for transmission to the bridge by the modem. The synthesizer receives encoded digital data streams and produces therefrom artificial speech at selected data rates that are inversely proportional to the number of external speakers. One technique used by the synthesizer is the use of overlap-add synthesis which allows for a particularly simple method for synthesizing multiple speakers. With the over-lap add technique a speaker's parameters, pitch voicing, and spectrum, are used to fill out an FFT buffer. The inverse transform is taken and summed in the usual overlap-add manner.

Abstract: A system for digital conferencing over narrowband channels which allows use by multiple 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.

Abstract: A system for digital conferencing over narrowband channels which allows use by multiple 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.

Abstract: 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.