Abstract: In a self-adpative echo canceller responsive to a receive-in signal and an echo signal resulting from the receive-in signal, a learning identification technique is implemented so as to exempt a send-out signal from the echo signal by successively varying an amount of modification (.DELTA.h.sub.j ') represented by .beta.eX, where .beta. represents a coefficient; e, a level of the send-out signal; and X, a level of the receive-in signal. A coefficient calculating circuit (28, 30, 35) calculates the coefficient .beta. from the factor and an incoming level (X) of the receive-in signal to determine the amount of modification. The coefficient is accompanied by a modifier given by 2X.sup.2 /(K+X.sup.2), where K represents a constant. The coefficient calculating circuit includes a unit (35) for calculating the modifier. The modifier may be multiplied by various factors of the amount of modification.

Abstract: An echo canceller comprising an adaptive finite impulse response filter receiving a receive signal and having its output subtracted from a send signal, a non-linear device for attenuating low level signals of the send signal and a noise injector for injecting noise into the send signal proportional to a dynamically measured background noise in the subtracted output. The non-linear device and the noise injector are disabled when the receive signal is below expected noise level or the send signal is at a high level relative to the receive signal.

Abstract: A conference table assembly comprises a plurality of conference tables each having a top providing a writing surface for a user, and a plurality of accessory units sandwiched between adjacent tables. Each of the accessory units has a top which is the same thickness as the conference table tops and is supported flush with them. In the accessory unit top there is an opening into a trough-like housing which is divided into compartments housing electrical and electronic components. The opening is closed by a removable panel on which are mounted such components as a goose neck lamp, microphone, keyboard, control elements, indicating instruments, etc. Preferably an accessory unit is provided between two user positions so that it can serve both. Each accessory unit preferably has a leg and foot so that it is self supporting and is provided with quick-release fasteners for connecting it to the tables.

Abstract: The filter coefficients of an echo cancelling arrangement having a near echo canceller and a distant echo canceller are initialized in accordance with a method and apparatus wherein the following steps are performed:transmission of at least two training sequences each comprising a pair of complementary S and C sequences having autocorrelation functions such that, if added, their sidelobes cancel, each S and C sequence being followed by a variable time interval .DELTA., determined as a function of the measured distant echo delay .tau.

Abstract: The subject suppressor is an improved form of echo suppressor used in conjunction with adaptive sub-band speech coders. The suppressor analyzes and uses N contiguous sub-bands of a sub-band speech coder. The intermediate results calculated during the normal operation of such speech coders may be analyzed in the suppressor to determine predictions for the echo levels of each sub-band and to set break in and break out thresholds. A substantial performance improvement with little increase in complexity over current echo suppressors is achieved. The subject suppressor may also be used with adaptive transform speech coders in which the corner frequency points define the edges of "sub-bands" for purposes of this invention. Sub-bands are defined here as contiguous segments of the frequency-energy spectrum.

Abstract: An automatic telephone silencer and volume controller having a microprocessor for storing time and volume information and for timely controlling the sound characteristics of a telephone ringer in accordance with the time and volume information stored. The time and volume information may be entered into the microprocessor by a suitable keyboard. Each time entry has associated with it a volume entry so that the telephone will ring at the prescribed volume from that time until the time denoted by the next time entry.

Abstract: In a loudspeaking telephone the power supply to the loudspeaker amplifier is shunted by a regulator which functions as a programmable Zener diode. Under conditions of low available line current, e.g. where two similar instruments are operated in parallel at the end of a long line, the regulator voltage is reduced in value to disable the amplifier and conserve power to maintain the basic operating functions of the telephone.

Abstract: This invention is a technique for providing isolation between the two channels of a handsfree telephone subset without resorting to gain switching or gain variations in the transmission path. The invention involves separating the frequency spectrum into two portions and allowing the stronger signal to capture a major portion of that available spectrum. Switched capacitor filters are used to control the degree of frequency bandwidth allocated to each channel while the filters are clocked from a common source assuring no possibility of overlap in the frequency spectrum. The affect of varying the bandwidth is much less noticeable than varying the amplitude and, therefore, creates much less user irritation.

Abstract: An arrangement for generating an electrical audio signal in response to a sound signal applied to a microphone in a reverberating room removes the reverberations with an adaptive filter. The filter learns or adapts so as to cancel the room echoes by receiving both the audio signal affected by reverberation and a clean audio signal from a highly directional local-acting microphone placed near the source of the sound. The signal to be filtered is applied to a transversal filter including a tapped delay line having variable taps or multipliers to produce incrementally delayed multiplied samples. The multiplied samples are summed, and the sum signal is subtracted from the clean signal to produce a difference signal. A .mu.P is programmed to iteratively calculate the effects of changes to the tap values and to select tap values which tend to reduce the magnitude of the difference signal. When the filter is converged, the difference signal is near zero.

Abstract: In order to prevent tap coefficient values from drifting toward excessively large values or divergence, an adaptive echo canceller is provided with a correction signal controller which (a) reduces the tap coefficient values upon the polarities of the tap coefficient signal and the tap coefficient correction signal coinciding and (b) increases the tap coefficient values upon the polarities differing.

Abstract: The invention relates to a supply circuit for a variable load, particularly for a line circuit in telephone systems.Conventional supply circuits, in which each of the two supply-current branches to the line wires contains the collector-emitter path of a transistor in series with an emitter resistor, offer a high AC resistance to voice-frequency voltages and longitudinal noise voltages, so that the bridging loss of the line remains small. To achieve a low AC resistance of the supply circuit to the longitudinal noise voltages, special measures in the control circuits of the transistors, particularly the use of a nonlinear element in the form of a CRD current-limiting diode in parallel with the controlled current path of each of the transistors, are proposed. These measures greatly reduce the amplitude of the longitudinal noise voltages at the inputs of subsequent circuits, which are thus protected.

Abstract: An apparatus for supplying current to a subscriber telephone set (R.sub.L) connected to a telephone exchange via a two-wire line departing from a a-wire and a b-wire output terminal in the arrangement. The arrangement includes two analogue amplifiers (2, 3) each with its output connected to said respective a-wire and b-wire output terminal, through which the combined DC-current and current representing the speech signal are fed out to the line. The apparatus further includes a voltage source with the pole voltage (E.sub.B) and its poles connected to two voltage supply inputs on each amplifier (2, 3), the output of the first amplifier (2, 3) being kept at a fixed potential. Three signal sources (5, 6, 8) are connected to the inputs of the amplifiers, the respective signal contribution of these sources being added for controlling the output magnitudes of the amplifiers. A first signal source (6) constitutes the reference signal source and has a fixed signal contribution.

Abstract: An apparatus for applying current to a subscriber line telephone set (RL) with associated two-wire line connected to a telephone exchange. The apparatus includes two analog amplifiers (5,6) each with its output connected to one of the two wires of the line, and feeding out on the line the combined DC current and current representing the speech signal. A DC/DC converter supplies voltage to an at least one of the amplifiers. To form a control voltage to the DC/DC converter, a cascade connection of a differential amplifier (1), a lowpass filter (2) and an adding circuit (3) are arranged between the line connection terminals and the control signal input of the DC/DC converter.

Abstract: An origination scan circuit for detecting circuit closure state in a loop circuit has a much lower impedance than does the typical loop circuit. Its source impedance is split into separate resistive parts for connecting opposite terminals of an office battery to the tip and ring leads of the loop. Currents in the separate resistive parts are sensed and summed for comparison against a threshold current to indicate whether or not a subscriber station on the loop is off hook. Threshold current magnitude is variable to accommodate loop start and ground start applications. When the off-hook state is detected, the origination scan circuit is disabled by switching open the resistive part connections, and loop current is thereafter provided by other suitable means. Automatic current limiting arrangements are included for converting the switching functions to high impedance circuit elements.

Abstract: An improved echo suppressor is described in which a more sophisticated echo canceller can be employed to derive optimum training coefficients for application to the echo suppressor. The canceller can be used on a shared basis among a large group of echo suppressors to provide periodic updating and adaptive training coefficients to each suppressor individually. The echo canceller operates in a supervisory role and is shared over a group of adaptive echo suppressors. The canceller trains each adaptive echo suppressor during a set up period for newly initiated voice traffic. The canceller is also responsible for initializing the parameters of a multi-parameter echo suppressor where the parameters are generated as a result of the coding technique employed. Upon completion of the initial parameter determination, the canceller is released and the echo control responsibility is transferred to the suppressor. The canceller is then free to initialize another suppressor when new traffic enters the system.

Abstract: A "high" pass filter is employed to shape the low frequency input characteristic to a bidirectional repeater including echo cancelers. This frequency shaping eliminates excessive low frequency signal components from being supplied to the echo cancelers. Consequently, the number of taps, i.e., amplitude coefficients, required in the echo cancelers is minimized.

Abstract: An interface is arranged between an integrated circuit which is provided for a 5 volt supply voltage and a variable-voltage telephone line. This circuit employs an MOS transistor whose current is controlled by a current regulating transistor and a current measuring resistor and includes a negative voltage feedback path for alternating current. A time constant is provided in order to disable the action of the current regulating transistor for transient or alternating currents.

Abstract: A method of reducing the convergence time of an echo canceller including a transversal filter having N coefficients comprises at least the following steps:transmission of a training data signal D(n) constituted by data transmitted at instants nT, T being the data interval, and being periodically reproduced after a duration LT at least equal to NT and having the property: ##EQU1## where d and d.sup.x are the value of the data signal D(n) and its complex conjugate value, respectively;calculation of the coefficients of the transversal filter carried out after the instant of appearance of the echo signal produced in response to said training signal in accordance with the expression: ##EQU2## where C and C.sub.o are the vectors of the N coefficients of the transversal filter at the beginning and at the end of the period of calculating the coefficients, respectively,e(n) is the difference signal,D.sup.x (n) is the vector of the complex conjugate values of the N data stored in the transversal filter, and.sigma..sup.

Abstract: A transmission configuration between a main station and a local station consists of a line which permits supplying of direct voltage power for stations from a source within the main station. A rectifier bridge is installed in such a manner that suitable polarization of the receiver can be achieved, regardless of the branching direction for wires comprising the line. Groups of unipolar current impulses are superimposed upon the supply voltage along the line by two generator units (K.sub.44, 40 and K.sub.50, 46) within the main station and a generator (K.sub.102, 100) within the local station. The respective polarities of impulses sent to and from the main station and the local station are such that said impulses can flow through rectifier bridges within local stations.

Abstract: An echo canceller for cancelling echoes which result from impedance mismatching in a two-wire/four-wire conversion circuit. The prior art employed an input terminal, an output terminal, a transmitter section, a receiver section, a digital-to-analog converter, an adaptive digital filter, a subtractor, a sample hold circuit, an analog-to-digital converter, a multiplier, a low pass filter, a hybrid circuit, and a two-wire communication path, for the purpose of generating a replica of the echo signal to cancel such echos. A method has also been proposed which employs a polarity discriminator circuit instead of an analog-to-digital converter, and utilizes approximation algorithms to correct an adaptive digital filter tap coefficient using the signs of an error signal.