Nec Corporation

Taisuke Sasada

Yasuhiro Wake

Hitoshi Fuda

Yuzo Fukushi

A signal receiving circuit receives sample data without an occurrence of discontinuity in the received sample data, even if the number of sample data to be transmitted from a transmitting terminal does not coincide with the number of sample data expected to be received by a receiving terminal. The signal receiving circuit has a converting circuit adapted to perform computations on npieces (nis a natural number) of first sample data to be sequentially input and to sequentially produce npieces (nis a natural number) of second sample data in response to a clock signal, and has a receiving section adapted to sequentially receive the npieces of the second sample data in response to the clock signal.

Signal receiving circuit and signal receiving method

Signals from microphones are first stored in memory circuits and then supplied to a cross-correlation arithmetic circuit following which a cross-correlation operation is carried out and cross-correlation function values are calculated for each time difference. An evaluation function circuit carries out addition processing of particular time intervals based on the cross-correlation function values and then searches for the maximum value to calculate time differences. Signals from the microphones are first stored in memory circuits and then supplied to a cross-correlation arithmetic circuit following which a cross-correlation operation is carried out and cross-correlation function values are calculated for each time difference. An evaluation function circuit carries out addition processing of particular time intervals based on the cross-correlation function values and then searches for the maximum value to calculate time differences. A position calculation circuit finds a horizontal direction angle and a vertical direction angle based on these time differences (delay).

Speaker direction detection circuit and speaker direction detection method used in this circuit

The echo canceler includes an N-tap FIR filter and a coefficient controller. Previous filter coefficients which were generated before an estimation error occurrence when the transmitting output signal becomes greater in power than the transmitting input signal are obtained by using only a number S of coefficient correction values and another number (N-1+S) of sequentially received signals. Since the latest (N-1) received signals are stored in (N-1) delay circuits of an N-tap FIR filter, respectively, a relatively small capacity memory may be provided to store the earlier S received signals. The number S is determined so that a time interval determined by the number S of sampling instants is longer than a response time of a double talk detector.

Recovery of previous filter coefficients with smaller capacity memory

A teleconference system comprises a plurality of microphones and a plurality of expanders connected respectively thereto for expanding the outputs of the microphones. A summing ammplifier produces a sum of the output signals of the expanders and feeds a compressor to compress the sum for transmission to a distant conference location. A desired signal from a given microphone has a higher level than undesired signals which may be detected by adjacent microphones, so it is emphasized by the associated expander with respect to the undesired signals. The compressor provides compression of the high- and low-level components of the sum in equal proportions so that the former is converted to a replica of the desired signal and the latter is suppressed to acceptable levels.

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Tokyo, Japan

Taisuke Sasada