Transcoders and mixers for voice-over-IP conferencing
View Patent ↗Transcoders and mixers having reduced algorithmic delay and processing complexity. An improved mixer for signals having encoded speech parameters wherein the parameters obtained through decoding are used by a parameter estimator to improve the encoding by providing a parameter estimate for the mixed signal. In the case of pitch parameters, the mixer uses the principle of strong-pitch-domination. The mixing of wideband signals is simplified by performing mixing of individual lower and upper sub-bands. A transcoder and a mixer that converts a wideband signal into a narrowband signal relies upon high frequency suppression. A transcoder and a mixer that converts a narrowband signal into a wideband signal relies upon filter combination.
1. A VoIP mixer for mixing a first input signal with a second input signal, the first and second input signals being signals having encoded therein a first and second correlation parameter, respectively, the VoIP mixer comprising:
(a) a first decoder for receiving the first input signal and generating a first decoded signal, the first decoder extracting the first correlation parameter from the first input signal;
(b) a second decoder for receiving the second input signal and generating a second decoded signal, the second decoder extracting the second correlation parameter from the second input signal;
(c) a mixer coupled to the first and second decoders, the mixer receiving the first and second decoded signals and producing a mixed signal;
(d) a parameter estimator coupled to the first and second decoders, the parameter estimator receiving the first and second correlation parameters and outputting an open loop parameter estimate; and
(e) an encoder coupled to the mixer and the parameter estimator, the encoder receiving the mixed signal and the open loop parameter estimate and outputting an encoded signal, wherein the encoder includes a closed-loop analyzer for creating the encoded signal and wherein the closed-loop analyzer employs the open loop parameter estimate;
wherein the correlation parameters include pitch data, the parameter estimator includes a pitch estimator, and the open loop parameter includes an open loop pitch estimate.
2. The VoIP mixer claimed in claim 1 , wherein the closed loop analyzer includes a closed loop pitch analyzer and the closed loop pitch analyzer employs the open loop pitch estimate as a starting point for closed loop pitch analysis.
3. The VoIP mixer claimed in claim 1 , wherein the pitch estimator selects the open loop pitch estimate based upon the input signal having strongest pitch energy, as defined by the pitch data.
4. The VoIP mixer claimed in claim 1 , wherein the first and second input signals are encoded according to a communications protocol selected from the group comprising G.729, G.729(A), and G.722.2.
5. A method for mixing a first input signal with a second input signal in a VoIP system, the first and second input signals comprising signals having encoded therein first and second correlation parameters, respectively, the method comprising the steps of:
(a) in a decoder, extracting the first and second correlation parameters from the first and second input signals, decoding the first and second input signals and outputting a first decoded signal and a second decoded signal;
(b) mixing the first and second decoded signals to produce a mixed signal;
(c) determining an open loop parameter estimate based upon the extracted first and second correlation parameters; and
(d) encoding the mixed signal, wherein the step of encoding includes performing a closed loop analysis to obtain a mixed signal correlation parameter for use in encoding the mixed signal, and wherein the closed loop analysis employs the open loop parameter estimate;
wherein the correlation parameters include pitch data, and the step of determining includes determining an open loop pitch estimate based upon the pitch data.
6. The method claimed in claim 5 , wherein the step of performing closed loop analysis employs the open loop pitch estimate as a starting point for closed loop pitch analysis.
7. The method claimed in claim 5 , wherein the step of determining includes selecting the open loop pitch estimate based upon the input signal having strongest pitch energy, as defined by the pitch data.
8. The method claimed in claim 5 , wherein the first and second input signal are encoded according to a communications protocol selected from the group comprising G.729, G.729(A), and G.722.2.