Abstract: A telephone installation has two talk-listen stations each comprising a telephone case adapted to receive talking and listening means housed in a common receiver case. At least one switch is provided on the telephone case or on the receiver case and is operable as a result of the raising and setting down of the receiver case on the telephone case. Each talk-listen station has a buzzer or like means and the listening means comprises an electroacoustic piezoelectric device with metallic electrodes arranged on either side of a piezoelectric material plate, one electrode being subdivided into two partial electrodes which are not interconnected in direct current-like manner. An oscillator arrangement is provided between the partial electrodes and the other electrode which produces a dial tone in one switching position of a switch and in the other switching position one of the partial electrodes and the said other electrode form the actual listening means, the other partial electrode being disconnected.

Abstract: A subscriber line interface circuit is provided for a telephone system for interconnecting a two-wire telephone channel with a four-wire telephone channel. The circuit includes a pair of power amplifiers employing complementary circuitry and being coupled in complementary fashion to the two-wire channel so as to provide for both DC electrical excitation to the two-wire channel, as well as providing for an impedance match over the voice frequency spectrum, thereby reducing power dissipation while improving the coupling of voice and/or data signals. The presence of any noise on power line is rejected by use of transistor biasing circuits and by use of feedback circuitry. Both resistive and capacitive feedback branches are provided for the impedance matching.

Abstract: A graphic equalizer comprises an equalizer for separately level adjusting the input signal for each of a number of divided frequency bands which are different from each other, control knobs provided one for each of the divided frequency bands, which are operated for carrying out level adjusting of the equalizer, a spectrum analyzer supplied with the output signal of the equalizer and having a display for displaying the level of each of the divided frequency bands, and a casing provided with a panel face having the control knobs and the display section of the spectrum analyzer disposed in a corresponding relationship to each other and accommodating the equalizer and the spectrum analyzer therein.

Abstract: In an interface circuit which couples a two-wire line of bidirectional transmission and unidirectional four-wire receiving and transmitting lines; in order to permit the interface circuit to operate in adaptation to the fluctuation of an impedance with the two-wire line side viewed from the four-wire receiving line, the four-wire receiving line is provided with a plurality of filters and a group of switches for selecting the filters, an output of the four-wire transmitting line is compared with outputs obtained by scanning the filters, and the filter providing the minimum output difference in the comparisons is selected and connected.

Abstract: A hybrid circuit having low return loss and low transhybrid loss is disclosed. An operational amplifier is employed in a feedback configuration. The receive port of the hybrid circuit is applied to the non-inverting input of the amplifier while the center-tap of the secondary winding of the hybrid transformer is applied to the inverting input of the amplifier. Most noticeable is the omission of an impedance setting resistor at the output of the operational amplifier. The circuitry connected to the transmit port and the two-wire bidirectional port of the hybrid circuit are of conventional design.

Abstract: A four-wire trunk line of a telephone network, operating with frequency-division multiplexing, is coupled by a hybrid coil to a local two-wire line and is provided, at a location separated from that hybrid coil by frequency modulators and demodulators, with an echo canceler connected across its receiving and transmitting branches. In order to eliminate frequency offset resulting from the incoherent modulation and demodulation, the echo canceler coacts with the phase-roll compensator comprising a phase-locking loop driven, during an acquisition phase, from a digital pilot-tone generator temporarily connected via a digital/analog converter to the receiving branch. The loop includes an analog/digital converter in the transmitting branch receiving the echo of the pilot tone due to hybrid-coil unbalance, a 90.degree.

Abstract: An echo canceller is used to cancel an echo signal occurring in the receive path of a data transmission modem in response to the signal appearing in the transmit path. This echo canceller comprises a controllable digital filter connected to the transmit path and adjusted by means of a control circuit, a difference circuit producing a residual signal resulting from the difference between the signal in the receive path and the synthetic echo signal supplied by the filter and an analog-to-digital converter which converts the residual signal into a digital control signal for the control circuit. In order to have the echo canceller function in a homochronous transmission system with an analog-to-digital converter having a reduced number of bits, the converter is controllable and is adjusted by the output signal of an attenuation circuit connected to the output of a circuit which detects the peak value of the residual signal.

Abstract: The test arrangement is intended to test, for example, a modem whose transmitter and receiver are coupled to the transmission line by means of a hybrid junction and comprises an echo canceller. The test consists of comparing a test signal applied to the transmitter with the signal restituted by the receiver when the modem is fedback from the line side. The test arrangement comprises an adder one input of which receives the error signal coming from the echo canceller, the other input receiving, during the test the feedback signal, its output being connected to the receiver. Means have been provided to make the signal restituted by the receiver different from the test sequence, when the error signal of the echo canceller exceeds a threshold.

Abstract: A full-duplex, two-wire Nyquist sampled data communication system includes an adaptive echo canceller (24) at each terminal (e.g., 10'). The echo canceller generates a replica (z.sub.m) of the echo component of each sample (r.sub.M) of the incoming signal. The replica and the sample are subtractively combined to provide an echo compensated signal (S.sub.M). During intervals of simultaneous transmission and reception, i.e., double talk, the echo compensated signal may contain not only an uncancelled echo component but also a far-end data component. An adaptation error signal generator (80), operating in response to a stream of recovered data symbols (e.g., a.sub.n), estimates and removes the far-end data component from the echo compensated signal and, in response to the difference, generates an adaptation error signal (.gamma.E.sub.M-D). This signal is applied as an error signal to the echo canceller.

Abstract: An echo canceller for use in a long-distance telephone network having a four-wire circuit and a two-wire circuit in which echoes are inherently produced at the junction of the four-wire circuit and the two-wire circuit. A sample interpolator converts the incoming digital signal into a digital signal having the same sampling rate as that of the outgoing digital signal on the basis of relative positions of sampling time for corresponding imaginary envelopes of the incoming and outgoing digital signals. An echo estimator produces an estimated echo signal responsive to the output of the sample interpolator for cancelling the echo signal. The estimated echo signal is substracted from the unprocessed digital signal to produce an echo-cancelled digital signal.

Abstract: An amplifier for acoustic signals provided with means for suppressing undersired acoustic feedback signals in a rapid manner. The amplifier includes a high-pass filter which separates a part of the signal to be amplified to obtain a control signal for reducing the gain of the amplifier when an acoustic feedback signal is detected. The output of the high-pass filter is connected to a periodicity detector, e.g. a single peak detector, which discriminates between an acoustic feedback signal having a regular periodicity and a signal having an irregular character, such as noise or speech. The control signal is derived from the output of the periodicity detector.

Abstract: An armored cord has flexibility and tensile strength for securing a telephone handset to a telephone housing. The cord includes an outer armored sheath which is designed for increased flexibility in that it allows the cord to bend readily over small radii. Tensile strength between the handset and housing is provided by an internal cable which absorbs the stress applied to the cord when subjected to unusually large longitudinal forces. The service life of the cord is lengthened, and the number of incidents causing out-of-service conditions is thereby reduced.

Abstract: A method and a system for rapidly attaining a large number of different sounds in an audio signal processing system. A preferred embodiment comprises an audio signal processing system which includes a main housing, containing a main circuit apparatus, cartridge-receiving recesses, and cartridges fabricated to be removably received in the recesses, each cartridge containing an audio effects circuit which affects the signal in a unique way to provide a different sound output. A plurality of electrical contacts of the recess and cartridge respectively provide disengageable connection of the audio effects circuit to the system.

Abstract: Direct voice communication with simultaneous two-way transmission is possible with a communicator having the earpiece of the communicator at one station connected by flexible plastic tubing to the mouthpiece of a communicator at another station, the two stations being connected by two independent voice channel tubes. The provision of cross-connected channels between the mouthpiece and the earpiece of two communicating stations permits normal conversation with simultaneous two-way transmission to occur in the manner of telephonic transmission rather than requiring sequentially alternating transmission between stations as necessary in using single voice tube communicators where destructive interference occurs between sound waves transmitted simultaneously in opposite directions in a voice tube.

Abstract: A hybrid circuit has its 4-wire path input coupled via a resistor to a 2-wire port and a non-inverting input of a differential amplifier, and via an active stage and another resistor to an inverting input of the differential amplifier, whose output is coupled to a 4-wire path output of the circuit and via a resistor to the inverting input. The active stage includes impedances, constituting a feedback arrangement or an input potential divider arrangement of an amplifier, which enable the hybrid circuit sidetone to be controlled or made substantially zero, without affecting the circuit's receive gain, even when the circuit is connected to a 2-wire path having a complex impedance.

Abstract: An energy discriminator is employed in conjunction with an adaptive filter to control updating of the filter transfer function characteristic. Specifically, the discriminator is employed to distinguish whether any significant received far end energy is only partial band or whole band. If the received energy is partial band the adaptive filter is inhibited from updating the transfer function characteristic during intervals that such energy is being received. On the other hand, if the received energy is determined not to be partial band and, hence, is whole band, the filter is enabled to update the transfer function characteristic during intervals that such energy is being received.In a specific example, the discriminator is employed in an adaptive echo canceler to inhibit updating an echo path estimate being generated by an adaptive transversal filter when partial band energy is being received and enabling updating of the echo path estimate when whole band energy is being received.

Abstract: A hybrid circuit composed of semiconductor current amplifiers without an inductance and large capacitance has been found. The DC speech current supplied by the DC power source (33) and the speech signal from the modem (28) are adjusted by the current amplifiers (17a, 17b) so that the subscriber line (2) is terminated with the predetermined impedance (600 ohms), and the speech signal from the subscriber line (2) is transferred to the modem (28) through the AC monitor circuits (24a, 24b). The common mode noise induced on the subscriber line (2) is cancelled by adjusting the input current of said current amplifiers (17a, 17b) by the common mode noise detector (22) and the common mode noise monitor circuits (23a, 23b). The speech signal from the modem (28) to the subscriber line (2) does not return to the modem (28) because of the cancellation operation by the return signal detector circuit (32).

Abstract: A transformerless hybrid circuit arrangement for a subscriber line interface circuit of a telecommunications exchange is disclosed. A preferred embodiment of the hybrid arrangement comprises a first and a second operational amplifier plus a differential amplifier connected together in the following manner: The non-inverting input of the first operational amplifier is connected to a first reference voltage and the output of this amplifier is connected (1) via a first resistor to one wire of the two-wire subscriber line, and (2) via a third resistor to the inverting input of the amplifier. The non-inverting input of the second operational amplifier is connected to a second reference voltage and to the receiving branch of the four-wire line of the telecommunications exchange.

Abstract: Arrangement for cancelling echo signals in data transmission over a two-wire transmission path. The data signals occurring in the send path are applied to an adjustable signal processing arrangement. From said data signals a synthetic echo signal (e(t)) is derived which is subtracted in a difference producer from the data signal occurring in the receive path. The residual signal (r(t)) is converted into a digital residual signal (r(j)) in an analog-to-digital converter arrangement. An interpolator which increases the sampling rate by a factor L results in the production of a digital control signal (r(i)) from the digital residual signal, for the setting arrangement. The sampling rate of the digital residual signal is M/LT Hz, wherein T is the duration of a data symbol in sec. and M and L represent integers which are relatively prime, L being greater than one.

Abstract: A method and a system of organizing, arranging and rearranging, the number and sequential order of audio effects circuit modules, by the changing, including inserting, removing, exchanging and interchanging, of said modules, providing noiseless, uninterrupted signal flow through a system during each of said changing operations. A preferred embodiment of the method comprises an audio signal processing system which includes a main housing, containing a main circuit apparatus, module-receiving recesses, and modules, fabricated to be received in the recesses, each module having an electronic circuit which affects the signal in a unique way to provide a different sound output. A plurality of switches and potentiometers lie on the main housing, and each module has markings indicating which controls on the main housing are to serve its operation.