Abstract: A network for matching an electrical source of audio signals to a piezoceramic driver for a high frequency loudspeaker. The network consists of all of the elements of a bandpass filter network, but with the parallel combination of an inductor and a capacitor in the output stage of the filter replaced by an autotransformer or autoinductor which transforms the input impedance of the piezoceramic transducer into an equivalent parallel capacitance and resistance which, together with the inductance of the autotransformer, supply the load resistance for the filter and replace the capacitor and inductor omitted from the output stage of the bandpass network. An additional shunt resistor may be placed across the output of the autotransformer to obtain the desired effective load resistance at the input of the autotransformer.

Abstract: A method and a system of organizing, arranging and rear-ranging 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 audio effect circuit which affects the signal in a unique way to provide a different sound output. A plurality of switches and potentiometers lie on either the main housing or the module, and each module has markings indicating which controls are to serve its operation.

Abstract: An echo control system for an adaptive echo canceller which forms a pseudo-echo or its residual signal by combining respective outputs from a tapped delay line holding an estimated characteristic of an echo path as a tap weight and receiving a received signal or its residual signal as an input signal, subtracts the pseudo-echo or its residual signal from an echo signal or its residual signal, and corrects the tap weight using an amount of correction obtained by the resulting residual echo signal or its residual signal and the received signal or its residual signal.

Abstract: A subscriber line interface circuit for coupling a balanced communication line with unbalanced bidirectional or a pair of unidirectional communication lines. Line current is fed to the line via a low resistance path for maximum current supply, via a circuit which matches the line impedance, and also provides high resistance protection to the output of amplifiers feeding the balanced line. Since a low resistance d.c. current feed is used, a voltage boost is not required. However lightning protection is obtained for the outputs of the amplifiers which feed the line, at the same time as virtually optimum line impedance matching and sufficient line current feed. The circuit is comprised of a balanced line including a lead pair, a pair of matched feed resistors for providing a low resistance path, each connected to one of the pair for applying a d.c. line current from a power source to the line, the total resistance of the feed resistors being a fraction of the d.c. line impedance.

Abstract: An echo canceller for passband data signals is comprised of a pair of real passband filters which generate samples of the echo replica in response to respective streams of rotated data symbol components.

Abstract: A signal transfer and processing system for use with a transmission line includes transmission line interface circuitry (30) and signal processing circuitry (100). The processing circuitry receives a signal to be processed, providing a processed signal for further use. An input bandpass filter (119, SW7) selectively limits bandwidth the input signal. A primary active frequency control (123) selectively controls the relative level of the signal provided from the primary bandpass filter means for selectively controlling the relative level of signal dynamics within different frequency bands for providing a frequency controlled signal, which is compressed by a compressor (127). A secondary active frequency control (135) selectively controls the relative level of the primarily compressed signal within different frequency bands to provide a frequency controlled primarily compressed signal which is further compressed by a secondary compressor (137).

Abstract: A snap-together housing is disclosed having a single fastener holding the multi-part housing together. The housing has a base, around which upper and lower panels fit in a clamshell arrangement. The wrap-around panels provide design contours and are the color bearing elements of the housing. Easy installation is achieved by a tab positioned at the rear of the lower panel which allows the lower panel to rotate upward around the base. A tab on the inner front surface of the lower panel engages a detent on the front of the base thereby preventing the lower panel from rotating downward without first being laterally separated from the base. The upper panel, held in position by a single fastener, interlocks with the front surface of the lower panel to prevent the lateral separation.

Abstract: In the circuit arrangement according to the invention, the two transistors with their main current lines connected in series cause no disturbance of balance in the subscriber's line. By means of exclusively alternating current coupling on the subscriber's lines wire leads, extension elements which cause no galvanic voltage drop can also be connected on. The series connection of the main current lines of the transistors may be run directly to the input of the amplifier emitting the outgoing signals.

Abstract: A circuit arrangement for connecting a communications set to a subscriber line of a subscription communication network in which each subscriber line includes two wires between which the communications set is conductively connected, which arrangement includes an operational amplifier having a noninverting input, an inverting input and an output, a setting transistor connected to have its conductive state controlled by the signal at the amplifier output and connected for influencing the current flowing between the two wires of the associated line and to the communications set, and circuit elements connected for applying to the amplifier inputs respective voltages proportional to the voltage between the two wires of the associated line and proportional to the current flowing between the two wires of the associated line and to the communications set.

Abstract: An electronic hybrid having a two-wire port adapted to be connected to a two-wire line and separate unidirectional receive and transmit ports, means for coupling signals received at said two-wire port to said transmit port, and a circuit for converting single-end signals imposed on the receive port into differential signals for application to the two-wire port.

Abstract: A balanced multiplier circuit for a subscriber loop interface circuit (SLIC) which provides both loop current to a two-wire bidirectional subscriber loop and suppression of longitudinal signals generated at the two-wire loop input to the SLIC while maintaining the midpoint load voltage at half the available power supply voltage applied to the SLIC.

Abstract: Energy in a received signal is distinguished as being whole band energy or partial band energy by comparing an average value of the received signal to a modified magnitude value of the received signal. A signal representative of the comparison result is supplied to a filter including hysteresis for generating a signal to control representative of whether whole band or partial band energy is present. Hysteresis is provided in generation of the control signal by comparing the output amplitude of the filter to a first threshold value when the control signal is a first state and then comparing the filter output amplitude to a second lower threshold value when the control signal is a second state. When the modified magnitude value exceeds the average value, the received signal includes whole band energy, otherwise the received signal includes only partial band energy.

Abstract: A transversal filter echo canceller includes two stores each for storing a set of coefficients for the transversal filter. The suitability of a set of coefficients stored in one of the stores is checked by supplying a pulse to the receive path and transversally filtering it, and comparing the level of the resultant transmit path signal, after subtraction of the transversally filtered pulse, with a threshold. At the same time the impulse response before the subtraction is stored in the other store. If the threshold is exceeded the functions of the two stores are interchanged and the check is repeated. The checking can be effected only once for a transmission line not subject to change, or, in the case of a transmission line which is subject to change, at the start of each telephone connection established via the line and optionally during conversation pauses during the connection.

Abstract: A signal processing system which can be readily adjusted to achieve a desired complex transfer function of arbitrary form. The system comprises a frequency sampling filter system from each individual filter of which in-phase and quadrature components are derivable. The sum of these components for all the filters is obtained to provide the output of the system, the proportions in which the components are summed being independently variable for each component, for example by adjustment of attenuators or multipliers. Such a system has particular application in the field of active sound control.

Abstract: A modular telephone jack is formed of two parts, top and bottom, which slide together, moving interengaging formations at a front end to hold the front ends together, and at least one detent at the other end of the top part with a resilient member in engagement with the detent to retain the two parts assembled. An additional feature, cantilever spring wire contact members are molded into the top part at one end of each contact member, the contact members extending into an aperture defined by the top and bottom parts.

Abstract: A four-wire termination circuit has a series arrangement of a current source controlled by a transmitting arm of a four-wire line and a first resistor. This arrangement is connected in parallel to a two-wire line terminal impedance formed by a second resistor and an impedance. The terminal impedance terminates the two-wire line in reflection-free fashion. Voltages dependent upon a transmitted signal current which are equal in value but opposed in phase appear across the first and second resistors. A voltage which is dependent upon a received signal current from the two-wire line appears across the second resistor. In a receiving arm of the four-wire line, an intermediate value voltage is present which is independent of the transmitted signal in the transmitting arm.

Abstract: A hybrid circuit includes a capacitive charge-transfer arrangement, comprising parallel capacitors and series switches,for coupling signals in one or both directions between a four-wire line and a two-wire line. The switches are constituted by VMOS power FETs. In one embodiment, the charge-transfer arrangement is provided in the receive path to give the desired properties of electrical isolation and unbalanced to balanced conversion of receive path signals. Signals from the two-wire line are coupled to a transmit path of the four-wire line via an attenuating and high-pass filtering arrangement and a differential amplifier, thereby providing good common mode rejection of high voltage signals, especially at power line frequencies. In another embodiment, the charge-transfer arrangement is provided, commonly for the receive and transmit paths, for coupling the two-wire line to the remainder of the hybrid circuit.

Abstract: A circuit for use with a subscriber loop interface circuit (SLIC) to detect the hook/switch status of the telephone handset driven by the SLIC. Responsive to metallic current flowing through the handset when the telephone is taken off hook, a voltage is derived which exceeds a threshold level as well as a current is produced which is proportional to the value of the metallic current. Whenever the produced current level is less than a predetermined value in conjunction with the threshold level being exceeded, a comparator threshold circuit is rendered operative to produce a signal indicative of the hook status being in a closed switch state. With the hook being in an open switch state, the voltage is caused to be less than the threshold level wherein the comparator threshold circuit is maintained in an non-operative state.

Abstract: Noise suppression apparatus is interposed between the transducer and the amplifier of a hearing aid, allowing the user to adjust the operation of an automatic level control circuit to provide suppression of background sounds with negligible effect on audibility of close-in sounds.

Abstract: Energy in a received signal is distinguished as being whole band energy or partial band energy by comparing an average value of the received signal to a modified magnitude value of the received signal. When the modified magnitude value exceeds the average value, the received signal includes whole band energy, otherwise the received signal includes only partial band energy.