Abstract: In a digital data transmission system including one or more matrix switches in which data in digital form is stored in a send memory during one selected time slot of a recurring time frame, transferred to a receive memory and sent out from the receive memory during another time slot of the recurring time frame to establish desired data paths through the switch between selected inputs and outputs, means is provided in the form of a programmable read only memory to control the insertion loss of each data path in a selective manner.

Abstract: A two-terminal tone generating hold impedance is disclosed which is powered from a central office telephone line and provides the functions of a hold impedance in a key telephone line circuit while providing an audio tone signal to an associated telephone line when the line is placed in a hold condition. The tone generating hold impedance consists of an oscillator circuit which is self-exciting upon the application of a dc voltage resulting from the connection of the tone generating hold impedance to the telephone line. In another embodiment a line powered music receiver functions as a hold impedance and applies music, received via radio or cable transmission, to the line placed in a hold condition.

Abstract: A station-to-station supervision system for a telephone system has a dual tone multiple frequency (DTMF) signal generator connected to the transmit line at each subscriber station, and a standard audible signal generator is connected to the receive line at each subscriber station for generating dial tone, ringback tone, reorder tone and busy tone in response to supervisory DTMF signals. Control means associated with each subscriber station effect the generation of a dial tone disable DTMF signal from a calling station in response to the combination of an off-hook condition at the calling station and the absence of a DTMF signal from any other station in the system; a busy tone command DTMF signal from any given station in response to the combination of an address signal for that station and an off-hook condition at that station; and a ringback tone command DTMF signal from any given station in response to the combination of an address signal for that station and an on-hook condition at that station.

Abstract: An audio echo control unit for a video teleconference system is provided with a suppression attack time which is a function of the microphone-to-audio speaker distance and a suppression hangover time which is a function of the room characteristics. Echo which results from a double-talk condition is eliminated by removing the break-in capability, and receive signal level modulation is eliminated by removing any variable loss devices from the transmission path.

Abstract: A switching apparatus comprising a switching circuit provided with a plurality of input terminals and a plurality of output terminals; a plurality of regenerative repeaters connected between the prescribed ones of said plural input and output terminals, the number of the regenerative repeaters being less than that of circuits through which signals of high error rate are expected to pass; and means for conducting signals from the prescribed input terminals to the output terminals directly or through the regenerative repeaters.

Abstract: The invention comes within the field of half echo-suppressor for four-wire telephone lines and relates more particularly to the transmitted speech detector, said suppressor comprising an accumulator for accumulating characteristic indices of the samples, to control of the blocking element in the send channel depending on the accumulated value.In accordance with the invention, there is provided at least one digital comparator with a threshold, which receives the content of the accumulator and whose threshold is fixed between the limits of the accumulator. The blocking element can therefore be controlled with several operation times and via different hold circuits.

Abstract: A modular interface device permits selective interconnection between telephone company network trunk lines and subscriber telephone lines. The device includes a housing having a removable protective cover and a first connector component having a plurality of contact elements aligned in at least two rows. The network trunk line conductors are electrically engageable with the contact elements so that each row of contact elements is associated with one tip or ring conductor, for instance. A second connector component is also provided having a plurality of second contact elements aligned in at least two rows. The subscriber telephone line conductors are electrically engageable with the second contact elements in such a manner that each row of second contact elements is associated with one of the subscriber line conductors.

Abstract: An electronic amplifying apparatus intended for electric music instruments (primarily guitar), with switchable circuitry offering an improved, specialized circuit for the enhancement of solo playing in addition to customary simple amplification. In the lead (or solo) mode of operation, the circuit will synthesize particular sustain and distortion characteristics and add them to the tone of the instrument (guitar, electric piano, microphone, etc.) to produce a more flexible and expressive sound for solo playing than the sound of the instrument normally amplified. Switching and control circuitry enable the musician to return to a conventional amplified tone which would be preferred for rhythm (or chordal) playing.

Abstract: A unit adapted to be connected to the tip party's subscriber's drop in a two-party line without requiring access to or rewiring of the tip party's telephone and having interconnected ringer isolator and ANI mark circuits. The ringer isolator and the ANI mark circuits may also be used individually.

Abstract: A peak-limiting apparatus and method particularly useful in systems employing high frequency pre-emphasis to compensate for steep high frequency rolloff in a receiver, or the like. The apparatus and method is useful in standard AM broadcasting to maximize loudness without noticeable distortion. The distortion caused by a clipper is determined by subtracting a clipper's output from its input. This distortion is compared in a plurality of critical bands with the input to provide a gain control feedback signal for a variable gain stage. The psychoacoustic phenomenon of "masking" is used to estimate maximum (non-audible) clipping.

Abstract: The first monostable multivibrator of a series connected pair of monostable multivibrators is responsive to each break interval of input dial pulses for establishing a fixed time delay after which the second multivibrator initiates a corrected break interval and starts a first timing capacitor thereof charging at a rate set by a fixed time constant. Each input break interval also causes a capacitor of a second timing circuit to start discharging at a rate set by another fixed time constant, the time that the second capacitor starts discharging being a function of the pulse repetition frequency of input dial pulses. When the charge voltages on the two capacitors are the same values, the output of a comparator resets the second multivibrator to terminate an output break interval so as to cause corrected dial pulses in the output thereof to have a constant percent break.

Abstract: A line/interface circuit for a key telephone system, which system is of the type including a subscriber telephone line manifesting a pair of conductors. The conductors emanate from a central office or PBX and the line/interface circuit provides interconnections between a key subset associated with said subscriber and said central office via said telephone line. The line/interface circuit has optical sensing means for producing a signal indicative of ringing to indicate an incoming call. Means are coupled to the optical sensing means to access the subset with an alternate signal. The subset is coupled for the transmission of voice signals to the telephone lines by means of a transformer to provide isolation. Additional means are provided to enable operation of the subset in a hold condition without releasing a connection between a connected party and the subset.

Abstract: A system for eliminating a noise from a stereo signal is disclosed comprising first and second signal paths to which an input stereo signal is applied simultaneously, storage means provided in the first signal path for storing an audio signal component, a pilot tone signal component and a sub-signal component of the stereo signal, the output of the storage means being grounded through a switch that is on when no noise exists, said switch being turned off when a noise exists in the stereo signal and extracting only the noise component by cancelling each signal component by its counterpart stored in the storage means, said noise component being phase inverted to be applied to the output of the second signal path.

Abstract: A subscriber loop extender for a telephone system in which a variable shunt conductance (41) is placed across the loop in response to a loop current indicating an off hook condition (32). An optical coupler (39) using a photo-resistor (41) or a photo-transistor as the variable conductance and a light source (40) responsive to loop current raises the value of the shunt conductance until sufficient current flows through the shunt to activate a central office relay (25). An SCR (48), the gate (47) of which is sensitive to the shunt current, extinguishes the light source thus removing the shunt from the loop. Loop current must fall to a level below the relay holding current to extinguish the SCR, thus providing hysteresis to the circuit. False ring trip is avoided by removing the shunt during each positive ringing pulse before its value increases so as to draw current to trip the ring. A second SCR (69) is provided to defeat slow decay of the photo-resistor conductance during dial pulses.

Abstract: A variable attenuation device is provided for an antenna amplifier by providing high attenuation and low attenuation signal flowpaths connected to the amplifier input by respective pin diodes. The biasing of the diodes and, thus, the attenuation factor provided, is controlled in proportion to the output of a rectifying circuit which, in turn, provides a DC output proportional to the magnitude of a given polarity of the AC signal supplied to the amplifier from inside the subscriber's home.

Abstract: A direct coupled transformerless hybrid for providing signal conversion between a balanced bidirectional transmission path and separate incoming and outgoing unidirectional transmission paths, for providing direct current to the bidirectional transmission path, for suppressing longitudinal mode signals originating in the bidirectional transmission path, and for providing signal balance to suppress transmission of reflected echoes from the incoming unidirectional transmission path to the outgoing unidirectional transmission path.

Abstract: A balanced/unbalanced converter circuit for connection to a subscriber's telephone line. A first Darlington transistor pair is connected as a controllable impedance between a first supply terminal and a first balanced input/output terminal. A second Darlington transistor pair is likewise connected between a second supply terminal and a second balanced terminal. A potential-summing resistive network is connected between the balanced terminals and the sum-representative potential is compared with a reference to provide a control signal to simultaneously change the impedances in opposite directions to correct any departure from balance. A third transistor controllable impedance circuit is connected in series with one Darlington transistor pair and used to regulate direct current flow through the line.

Abstract: A telephone is provided which simulates the old-fashioned crank-type of wall telephone in all respects, and yet which is constructed for modern dial or Touch-Tone operation. The telephone includes a rectangular housing which is intended to be mounted on the wall, and which has a rectangular hinged cover. The electrical components of a present-day telephone are mounted within the housing, and are connected to an old-fashioned transmitter and receiver. The transmitter is mounted on the front of the housing, and the receiver is removably supported on a pivotally mounted hook at one side of the housing. A mechanical linkage is provided which serves to couple the switching mechanism included in the present-day telephone to the hook on the side of the housing.

Abstract: A pulse shaping circuit, for use with two-wire telephone station sets, such as normally associated with electronic private automatic branch exchange systems. The function of the pulse circuit is to regenerate hook-switch and hold-button control signal pulses for transmission to the common switching equipment as finite loop current interruptions of predetermined pulse width. The circuit overcomes false signalling and signal recognition problems caused by loop-current transient interruptions, and by imprecise manual operation of the station hook-switch and hold-button by station users.

Abstract: Telephone loop feed apparatus in which a hybrid couples audio signals to and from the subscriber loop and presents a high impedance to the loop relative to the loop impedance. DC power is coupled to the loop by matched resistors which determine the loop feed matching resistance. DC power is blocked from the hybrid to avoid saturation.