Abstract: An arrangement for adjusting an adaptive digital balance filter included in a subscriber unit connected to a telephone line includes a selection unit, which can be connected to the subscriber unit either via the exchange or via a separately arranged switch. When the selection unit is connected to the subscriber unit, the balance filter is disconnected from both branches of the subscriber unit. A test signal generator is included in the selector unit for sending a signal on the lines via both branches of the subscriber unit. There is further included a plurality of digital filters wherein the transfer function of any of the filters closely coincides with the transfer function of the filter formed by the line impedance and the portion of the subscriber unit which is connected to the line and to the balance filter.

Abstract: A passband echo canceller achieves improved performance by providing a signal having a substantially uniform power spectral density to an adaptive echo canceller; the improved input signal is substantially uniform from approximately zero hertz to one half the operating or sample frequency of the echo canceller. This signal may comprise that range of frequencies occupied by the transmitted spectrum with added out of band noise.

Abstract: 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.

Abstract: Transmission and reception of first and second information signals over a telephone local loop, simultaneous with voice communications over the same local loop, is possible if the phase and amplitude of said first and second signals are perfectly balanced. The inventive apparatus detects differences in phase and amplitude between said first and second signals, and generates digital control signals to reduce the phase and amplitude differences to zero. Adjustment of phase and amplitude is completely automatic and rapidly accomplished.

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: Echo canceler associated with a modem utilizing amplitude and phase modulation of a carrier, the echo canceler comprising adaptive filters (16-1) to (16-p) producing signals which are combined in an adder (15) for forming a synthetic echo signal .epsilon.(n). The coefficients of these filters are adjusted to minimize the mean square value of the residual echo signal e(n)=.epsilon.(n)-.epsilon.(n), where .epsilon.(n) is the echo received. The echo canceler comprises a code conversion circuit (17) which receives a signal D(n) characterizing in each modulation interval the amplitude and phase state of the carrier to be transmitted and which produces distinct configurations of several numbers of values +1, -1 or 0, said distinct configurations corresponding to the distinct possible states of the carrier to be transmitted such that elementary signals D.sub.1 (n) to D.sub.p (n) are formed which are mutually independent in the mean and which are applied to the filters (16-1) to (16-p).

Abstract: An arrangement for cancelling the composite echo signal formed by, for example, a linear component and a variable-phase component, comprises a linear echo canceller and a variable phase echo canceller, the difference circuits of these echo cancellers being arranged in cascade. The adjustable signal processing arrangements of each echo canceller are controlled for minimizing a predetermined function (mean square value or time average of this means square value), either of a residual echo signal appearing at the output of the difference circuit of this echo canceller itself or of a residual echo signal appearing at the output of the cascade arrangement of the difference circuits. In all cases the signal at the output of the linear echo canceller contains only a residual variable-phase signal which can be compensated for by the variable-phase echo canceller.

Abstract: In an echo canceller system of the type comprising a circuit for measuring the characteristic of an echo path in accordance with input/output signals of the echo path and cancelling from an actual echo signal an approximate echo path signal synthesized in accordance with the echo characteristic, a level measuring circuit for measuring the level of the residual signal, a residual echo level estimating means for estimating the residual echo level based on the output of the level measuring circuit, and a comparator comparing the output of the residual echo level estimating means with the output of the residual echo level measuring circuit, the output of the comparator controlling the measuring operation of the echo path, there are provided a residual signal level measuring circuit including the residual signal level measuring circuit, a transmitted signal input level measuring circuit, and a detector for detecting an opened state of the echo path and producing an output which controls the residual signal level m

Abstract: An armored cord and handset wherein the strength member of the armored cord is secured to the handset through resilient means and the sheath member of the armored cord is secured to the handset via a securing member which is provided with reinforcing means.

Abstract: In accordance with the present invention, local loop testing in an echo canceller based modem is provided in a manner in which proper operation of both the receiver and echo canceller can be assessed simultaneously. Specifically, the modem includes means for generating data and interfering symbol sequences and for applying the interfering sequence to both the echo canceller and the modem transmitter, while applying the data sequence only to either the transmitter or the echo canceller. During closed loop testing, the modem connection to the transmission line is opened, and a portion of the output of the modem transmitter is applied to the modem receiver via a leakage path through the hybrid. The received symbol is subtracted from the echo canceller output, resulting in application to the receiver of only a version of the data symbol sequence. Advanced knowledge of the characteristics of the data symbol sequence allows proper receiver operation to be verified.

Abstract: The device for providing protection against echoes includes a level memory (33) for storing a value Gs and a comparator (34) for comparing the level Gx provided by an AGC device (31) upon receipt of a message with a value Gs stored in the level memory (33) and for supplying a resetting signal to the equalizer (35) for resetting the coefficients thereof to zero together with a signal for storing the level Gx as a new value Gs in the level memory (33) where Gx exceeds Gs by a predetermined value, or for supplying a signal for inhibiting the decoding of the data signals where Gx falls short of Gs by a predetermined value, thereby indicating that the received message is an echo.

Abstract: Echo canceler associated with a modem utilizing amplitude and phase modulation of a carrier, the echo canceler comprising adaptive filters (16-1) to (16-p) producing signals which are combined in an adder (15) for forming a synthetic echo signal .epsilon. (n). The coefficients of these filters are adjusted to minimize the mean square value of the residual echo signal e(n)=.epsilon.(n)-.epsilon.(n), where .epsilon. (n) is the echo received. The echo canceler comprises a code conversion circuit (17) which receives a signal D(n) characterizing in each modulation interval the amplitude and phase state of the carrier to be transmitted and which produces distinct configurations of several veral numbers of values +1, -1 or 0, said distinct configurations corresponding to the distinct possible states of the carrier to be transmitted such that elementary signals D.sub.1 (n) to D.sub.p (n) are formed which are mutually independent in the mean and which are applied to the filters (16-1) to (16-p).

Abstract: A loudspeaker system includes at least two loudspeaker drivers, together with an electrical crossover network having filter circuits with at least two separate mutually exclusive frequency passbands. The filter circuits comprising the crossover network each possess brick-wall amplitude responses, i.e., passbands with very high band-edge amplitude vs. frequency response slops, on the order of 100 dB/octave in the better embodiments. The high passband band-edge slopes, which are realized by the inclusion of transmission zeros in the separate crossover filter transfer functions, takes together with further appropriate crossover filter transfer function synthesis causes the separate loudspeaker drivers comprising the loudspeaker system to function independently of one another in their contribution to total system acoustic output.

Abstract: A telephone set housing (1) is disclosed having at least one cradle (2) arranged in a base component of the housing for receiving the handset. In the region of the cradle, a filler body (5) is provided which, for a desk application of the telephone set housing (1), flushes with the cradle (2), whereas, for the use of the telephone set (1) as a wall-mounted set, a projection (1) which is integrally connected to the filler body projects beyond the contours of the cradle (2). The filler body (5) is secured in such manner that the subscriber himself/herself can easily convert the telephone set housing (1) for desk or wall-mounted application. For this purpose, there is provided at least one freely accessible recess (3) in the region of the cradle (2) into which recess the filler body (5) can be inserted by means of a catch connection in two operating positions.

Abstract: An amplifier for acoustic signals provided with means for suppressing undesired 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: A signal processing system is disclosed for processing dynamically varying intelligence-carrying signals represented by different frequencies by transferring these signals within a pass band narrower than the range of the frequencies. The system, although not a compressor or compandor system, makes use of a compressor circuit for compressing only signals within a predefined pass band. Active filter circuits shape the compressed signals into a predetermined power envelope having fundamental frequency signal components and harmonically related constituents of the fundamental frequencies. Another compressor circuit is used for further compressing signal constituents of the power envelope. A negative feedback arrangement provides dynamic limiting of compression by the first compressor circuit as a function of increase of compression by the second compressor circuit.

Abstract: The invention relates to a telephone subscriber electronic feeding bridge which includes a transformer with three windings, between the line of the sub set and the connection network of the telephone unit automatic exchange or autoswitch of which it forms a part. A capacitor is interposed on one of the two wires of the line, connected furthermore to feed resistors. The third winding of the transformer, associated with the winding of the line of the set, is looped on a negative impedance. This arrangement allows impedance matching both in direct current and in alternating current.

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: An adaptive hybrid circuit for use in a digital telephone switching system is disclosed. The hybrid circuit is adaptive in that it provides cancellation of a far end talker power component in an output signal having both far end talker and near end talker power components. The circuit includes first and second transfer filters for matching loaded and non-loaded subscriber loops, respectively, in the telephone system. The circuit generates a filtered signal representing the difference between loaded and non-loaded subscriber impedances in the telephone system and generates an adaptive control signal responsive to the filtered signal and the output signal such that the far end talker power component is cancelled.

Abstract: A tone disabler is designed for use in a full duplex data transmission system adapted to send a tone before each transmission of data and to reverse the phase of such tone during a later half of a full duplex data transmission. Both the tone and the phase reversal are detected. Responsive to a coincidence of such detections, a control signal is given to disable an echo canceller. The control signal is fed back to latch the control signal as long as the tone is present.