Wideband speakerphone
Processing requirements for acoustic echo cancellation in voice communications are significant and are even more so as the bandwidth of the communication increases. Whilst voice communication occupies a relatively narrow band of frequencies the processing requirements and so forth for wideband communication render acoustic echo cancellation difficult to achieve in a cost effective manner. The invention provides for acoustic echo cancellation within wideband communications by dividing the communications into sub-bands and applying acoustic echo cancellation to some sub-bands whilst processing other sub-bands according to the status of the communications. Additional sub-bands are transmitted at either full-duplex or half-duplex.
1. A speaker phone system comprising:
a receive channel for receiving a first signal from a far end device over a duplex communications link for conversion to an acoustic signal on a local speaker;
a transmit channel for receiving a second signal from a near end transducer for transmission to the far end device;
respective filters at inputs of the receive and transmit channels to split each of said transmit and receive channels into at least two pairs of frequency bands, wherein each frequency band in the transmit channel is paired with a frequency band in the receive channel;
an echo canceller for performing adaptive echo cancellation in at least one pair of frequency bands;
a half-duplex controller for imposing half-duplex operation in the transmit and receive channels in at least one other pair of frequency bands;
a summer at an output of each channel for recombining the frequency bands.
2. A speakerphone system as claimed in claim 1 , further comprising a down-sampler at the input and an up-sampler at the output of each channel in said at least one pair of frequency bands.
3. A speakerphone system as claimed in claim 1 , wherein the frequency bands in each pair of frequency bands correspond to the same range of frequencies.
4. A speakerphone system as claimed in claim 1 , wherein the transmit and receive channels are split into two pairs of frequency bands and the echo canceller is arranged to perform echo cancellation in the pair of frequency bands with the lower frequency.
5. A speakerphone system as claimed in claim 1 , further comprising variable gain attenuators in at least one other pair of frequency bands in the transmit and receive channels controlled by the half-duplex controller.
6. A speakerphone system as claimed in claim 5 , further comprising a variable gain attenuator in the frequency band of said one at least pair of frequency bands in the receive channel.