Transcoders and mixers for voice-over-IP conferencing

A VoIP mixer for mixing a first input signal with a second input signal, the second input signal comprising a wideband signal having a lower sub-band component and an upper sub-band component, the VoIP mixer comprising:

• (a) a transcoder comprising:
• a narrowband decoder for receiving the first input signal and outputting a decoded signal;
• a first filter for receiving the decoded signal and outputting a first lower sub-band signal, the first filter having a transfer characteristic for introducing a first artificial aliasing into the decoded signal to produce the first lower sub-band signal;
• a second filter for receiving the decoded signal and outputting a first upper sub-band signal, the second filter having a transfer characteristic for introducing a second artificial aliasing into the decoded signal to produce the first upper sub-band signal;
• and
• a wideband encoder for receiving the first lower sub-band signal and the first upper sub-band signal, encoding the first lower sub-band and first upper sub-band signals, and producing an output signal;
• wherein the transcoder excludes an up-sampler and excludes a quadrature mirror filter;
• (b) a wideband decoder for receiving the second input signal and producing a second lower sub-band signal and a second upper sub-band signal;
• (c) a lower sub-band mixer for mixing the first and second lower sub-band signals and producing a mixed lower sub-band signal;
• and
• (d) an upper sub-band mixer for mixing the first and second upper sub-band signals and producing a mixed upper sub-band signal;
• wherein the mixed lower sub-band signal and the mixed upper sub-band signal are input to the wideband encoder, which produces the output signal.

A method for converting a first input signal to an output signal in a VoIP system, the first input signal comprising a narrowband signal and the output signal comprising a wideband signal, the method comprising the steps of:

• (a) narrowband decoding the first input signal to produce a decoded signal;
• (b) filtering the decoded signal to produce a first lower sub-band signal, wherein said filtering includes introducing a first artificial aliasing into the decoded signal to produce the first lower sub-band signal;
• (c) filtering the decoded signal to produce a first upper sub-band signal, wherein said filtering includes introducing a second artificial aliasing into the decoded signal to produce the first upper sub-band signal;
• and
• (d) wideband encoding the first lower sub-band signal and the first upper sub-band signal to produce the output signal;
• wherein the method excludes up-sampling the decoded signal and wherein filtering excludes the use of quadrature mirror filters.

A method for mixing a first input signal with a second input signal in a VoIP system, the second input signal comprising a wideband signal having a lower sub-band component and an upper sub-band component, the method comprising the steps of:

• narrowband decoding the first input signal to produce a decoded signal;
• filtering the decoded signal to produce a first lower sub-band signal, wherein said filtering includes introducing a first artificial aliasing into the decoded signal to produce the first lower sub-band signal;
• filtering the decoded signal to produce a first upper sub-band signal, wherein said filtering includes introducing a second artificial aliasing into the decoded signal to produce the first upper sub-band signal;
• wideband encoding the first lower sub-band signal and the first upper sub-band signal to produce an output signal;
• wherein the method excludes up-sampling the decoded signal and wherein filtering excludes the use of quadrature mirror filters;
• wideband decoding the second input signal to produce a second lower sub-band signal and a second upper sub-band signal;
• mixing the first and second lower sub-band signals to produce a mixed lower sub-band signal;
• and
• mixing the first and second upper sub-band signals to produce a mixed upper sub-band signal;
• wherein the step of wideband encoding includes encoding the mixed lower sub-band signal and the mixed upper sub-band signal to produce the output signal.