Nec Corporation

Nippon Electric Co., Ltd.

Nippon Telegraph and Telephone Public Corporation

Hisashi Fujisaki

Keiko Shimada

Masakazu Nishino

A branched telephone system having a plurality of telephones which are connected to a single subscriber line or to single radio apparatus functions to establish a priority set condition in which the communicating function of particular one of the telephones is validated to prevent the other telephones from being used, and further includes the function of automatically cancelling such a priority set condition.

Branched telephone system

A loud speaking telephone has separate volume level control circuits positioned in the transmit and receive paths, respectively. The frequency is shifted in at least one of the paths to provide a signal which is less likely to produce echos or singing. A comparator compares the levels in the send and receive paths to produce a control signal. The control signal adjusts the volume level controls to prevent singing.

Loudspeaking telephone with a frequency shifting circuit

A voice controlled automatic dialer comprises a speech analyzer for generating a signal representative of characteristic patterns of an input utterance entered through a microphone, and a first memory for storing a plurality of reference signals representative of predetermined characteristic patterns of utterances of dialing numbers and command words, the predetermined characteristic patterns being representative of utterances common to any users. A second memory stores a plurality of reference signals representative of specific characteristic patterns of utterances of dialing names which are defined by authorized users. The output signal of the speech analyzer is compared with the reference signals stored in the first and second memories and an output is generated as representative of least distances between the characteristic patterns of the input and the stored patterns. The result of the comparison is indicated by a synthesized speech or a multifrequency tone to permit users to confirm the validity of the input utterances. A manually operated switch couples the output of the speech analyzer to the second memory when it is desired to store a user-specific dialing name into the second memory after a training process.

Voice controlled dialer with separate memories for any users and

A terminal station operating with a current supplied from a master station exchanges signals with it through cable conductors, one of the cable conductors being grounded at the master station to allow the current to return from the terminal station. A receive circuit is formed by a first differential amplifier and a first resistor network connected in a balanced relationship to input terminals of the first differential amplifier for receiving a signal from the master station in a noise-cancelling relationship with respect to the ground potential to eliminate the effect of noise generated by the passage of the current through the ground conductor. A transmit circuit includes a second differential amplifier and a second resistor network connected in a balanced relationship to input terminals of the second differential amplifier for transmitting a signal to the master station in a noise-cancelling relationship with respect to the ground potential to eliminate the effect of the noise at the output of the second differential amplifier.

Noise-free terminal station compatible with existing master stations

A loudspeaking telephone system has a voice switch circuit in which voice signals on transmission and reception speech channels are respectively detected to produce control signals, and these control signals are compared to judge the levels of the voice signals on both the speech channels so that the switching between both the channels is effected under the control of loss of variable attenuators inserted in both the speech channels. The control signals corresponding to the voice signals on both the transmission and reception speech channels are converted through analog-to-digital conversion into digital values which are suitable for arithmetic operation. The arithmetic operation is such that the losses of the variable attenuators are automatically controlled in accordance with the use conditions of the loudspeaking telephone system to minimum values which can prevent the howling, transmitting blocking and receiving blocking.

Loudspeaking telephone system

A bandpass filter is disclosed which includes a low-pass filter and an analog delay circuit in which the delay time is set by a clock signal. THe analog delay circuit samples the voltage of the low-pass filter capacitor and delays the sampled voltage according to the clock signal. The output of the analog delay circuit is then used to equalize within a certain period of time the voltage of the low-pass filter capacitor. The analog delay circuit may consist of an integrated circuit BBD (Bucket Brigade Device) or CCD (Charge Coupled Device).

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Tokyo, Japan

Hisashi Fujisaki