Abstract: A method and system for performing audio signal processing is provided. A phase of a signal may be shifted between 0° and 360° for all frequencies of the signal, without any significant delay distortion. The phase shift can be accomplished through the use of two signal outputs (which are each shifted in phase by 90° relative to the other), inverters and an analog summing circuit. Selective use of the inverter on one or both of the 90° phase shifted outputs, and their linear combinations, allows the phase of the audio signal outputs to be shifted between about 0° and about 360° by a recording engineer, for example.

Abstract: A method and system for performing audio signal processing is provided. A phase of a signal may be shifted between 0° and 360° for all frequencies of the signal, without any significant delay distortion. The phase shift can be accomplished through the use of two signal outputs (which are each shifted in phase by 90° relative to the other), inverters and an analog summing circuit. Selective use of the inverter on one or both of the 90° phase shifted outputs, and their linear combinations, allows the phase of the audio signal outputs to be shifted between about 0° and about 360° by a recording engineer, for example.

Abstract: A two-wire line conditioning apparatus utilizing dial tone for alignment. Variable impedances are iteratively adjusted using a multitone calibration signal. The hybrid device filters out dial tone components in measuring the echo of the multitone signal during the variable impedance adjustment. The level of the dial tone is measured to determine the overall gain that is to be inserted on the line by the line conditioning apparatus.

Abstract: The present invention provides a two-wire line conditioning apparatus having an improved calibration and cancellation circuit and provides an improved calibration method using a multitone calibration signal. The apparatus automatically adjusts an electronic hybrid as part of a calibration procedure so as to eliminate undesirable echo effects when calls are placed along the line. The alignment procedure identifies the optimal balance in a rapid manner. The electronic hybrid balancing process and echo cancellation circuitry may also be utilized in a circuit for converting four-wire communications systems to two-wire communications systems. The line conditioning device of the present invention utilizes a multitone signal to simulate the voice frequency spectrum between approximately 500 Hz and 3500 Hz to probe the line side with a plurality of tones (e.g., 500, 1500 and 3500 Hz; or 500, 1000, 1500, 2000, 2500, 3000, 3500 Hz).

Abstract: The present invention provides a two-wire line conditioning apparatus having an improved calibration and cancellation circuit and provides an improved calibration method using a multitone calibration signal. The output is monitored by an AGC circuit which controls the output, and prevents hard clipping. This is particularly important for DTMF receivers. Additionally, the apparatus automatically adjusts an electronic hybrid as part of a calibration procedure so as to eliminate undesirable echo effects when calls are placed along the line. The electronic hybrid balancing process and echo cancellation circuitry may also be utilized in a circuit for converting four-wire communications systems to two-wire communications systems. The line conditioning device of the present invention utilizes a multitone signal to simulate the voice frequency spectrum between approximately 500 Hz and 3500 Hz to probe the line side with a plurality of tones (e.g., 500, 1500 and 3500 Hz; or 500, 1000, 1500, 2000, 2500, 3000, 3500 Hz).

Abstract: The present invention provides a two-wire line conditioning apparatus having an improved calibration and cancellation circuit and provides an improved calibration method using a multitone calibration signal. The apparatus automatically adjusts an electronic hybrid as part of a calibration procedure so as to eliminate undesirable echo effects when calls are placed along the line. The hybrid has capacitors and resistors which can be switched into and out of the circuit by using simple transistor devices. The electronic hybrid balancing process and echo cancellation circuitry may also be utilized in a circuit for converting four-wire communications systems to two-wire communications systems. The line conditioning device of the present invention utilizes a multitone signal to simulate the voice frequency spectrum between approximately 500 Hz and 3500 Hz to probe the line side with a plurality of tones (e.g., 500, 1500 and 3500 Hz; or 500, 1000, 1500, 2000, 2500, 3000, 3500 Hz).

Abstract: The present invention provides a two-wire line conditioning apparatus having an improved calibration and cancellation circuit and provides an improved calibration method using a multitone calibration signal. The apparatus automatically adjusts an electronic hybrid as part of a calibration procedure so as to eliminate undesirable echo effects when calls are placed along the line. The results of the balancing procedure are examined, and the values of the resistance and capacitance from the balanced ciruit are compared to determine whether the line is loaded or non-loaded. The electronic hybrid balancing process and echo cancellation circuitry may also be utilized in a circuit for converting four-wire communications systems to two-wire communications systems. The line conditioning device of the present invention utilizes a multitone signal to simulate the voice frequency spectrum between approximately 500 Hz and 3500 Hz to probe the line side with a plurality of tones (e.g.

Abstract: A ground fault detector for TI span equipment for transmitting signals from a central office to a network interface unit and receiving signals at the central office from the network interface unit. The TI span equipment includes a first pair of cables for transmitting data payload from the central office to the network interface unit and a second pair of cables for receiving data payload at the central office from the network interface unit. A line repeater is located along the TI span equipment between the central office and the network interface unit. The line repeater includes a transformer with core and a first, second, third and fourth coil. The coils are coupled to the transmit and receive span, and the transformer core saturates when the current differential between the coils exceeds a predetermined level. When the core is saturated, signals present on the first coil are not imposed on the second coil.

Abstract: A protect circuit that may be interconnected to two different data transmission lines and that provides enhanced error correction. The circuit includes first and second line build-out circuits and fixed delay buffers interconnected to the two transmission lines, as well as a controller and switch. The build-out circuits allow the data bits received from the two data transmission lines to be correlated. Each of the fixed delay buffers has a predetermined length and holds a sequence from one of the two transmission lines. The controller tests the correlated data bits from the build-out circuits to determine whether any coding rule violation has occurred. If a coding error, such as, for example, a hi-polar violation, is detected, the contents of the fixed delay buffer that includes the bit that does follow the predetermined coding rule is transmitted to the receiving station. Thus, both of the transmission lines are utilized in order to enhance the accuracy of the data transmitted to the receiving station.

Abstract: A system for monitoring the performance of T1 digital transmission lines by incorporating a common unit interconnected to a plurality of network interface units as well as to a spare transmission line leading to a central office. The common unit is configured to interrogate any or all of the network interface units in order to obtain status information such transmission error rates, and to report such status information via the spare transmission line to the central office. By dedicating a common unit to oversee error detection and/or status reporting, communication between the central office and customer premises equipment need no longer be disrupted while transmission performance is being monitored.

Abstract: An out of band data link for performance monitoring information using existing telecommunications transmission facilities. The Bell telephone network includes a variety of central offices and network interface units that should communicate with each other regarding performance. The data link allows the network interface unit to advise the telephone company's central office of difficulties. A first modem is interconnected between a pair of simplex leads in the central office telephone company's central office repeater transformers, and a second modem is interconnected between a pair of simplex leads in the network interface unit's transformers. The voltage between each pair of leads is used to effect communication between the telephone company's central office and the network interface unit.

Abstract: A network interface unit interconnected between a network span and a customer premises. The network span includes network transmit lines and network receive lines. The network interface unit includes a passive resistance circuit in the receive direction path that allows monitoring of signals from a central office in the presence of open circuit reflection or noise from the customer premises.

Abstract: An improved address acknowledgement system for line elements such as repeaters in a digital telecommunication network. The system is preferably controlled by logic circuitry, in conjunction with a microprocessor. A remote facility such as a test unit transmits to the repeater a loopup command, requesting the repeater to enter loopback mode. The repeater acknowledges receipt of this command by inverting its address and transmitting the inverted address back to the test set. The test set either scans its incoming data stream for the inverted address of the line element or inverts the incoming data stream and scans the inverted incoming data stream for the non-inverted address of the line element. In either case, another line element bearing the same non-inverted address as the line element targeted to enter loopback will not interpret the inverted address as a loopup command. Accordingly, other line elements will not thereby be unintentionally caused to enter loopback mode.

Abstract: A longitudinal cancellation circuit for use in circuits providing a received differential signal containing a desired differential component and an undesired longitudinal component has a first multiplier for multiplying received differential signal with the longitudinal signal to produce a first signal having at least a DC component in addition to other frequency components. The first signal is received by a low-pass filter which produces a second signal containing only the DC component. A second multiplier multiplies the second signal with the undesired longitudinal signal to produce a third signal equal to the to the undesired longitudinal component. The third signal is subtracted from the received differential signal to produce the desired differential signal which is free of undesired longitudinal component.

Abstract: The microprocessor unit of a system implemented using metal-oxide-silicon (MOS) technology, is driven by a variable-frequency clock. The microprocessor controls the clock frequency based on the present rate of required microprocessor activity. By driving the microprocessor unit at a lower clock frequency when such activity rate is low, the energy dissipated by the microprocessor unit is reduced due to the MOS power-frequency characteristic.

Abstract: An arrangement to compensate for the leakage and biasing characteristics associated with the semiconductor crosspoints of a concentrator to allow accurate telephone subscriber loop measurements to be made through the concentrator. A compensation current is supplied which varies linearly with the applied test voltage according to a relationship that is determined adaptively just prior to the test so that the effects of device differences and temperature variations are minimized. The approach is extended to nonlinear compensation.

Abstract: A very low power asymmetrical polarity marking signal which may be the sum of a cosine wave and its coherent second harmonic is added to a symmetrical message signal before transmission. At the receive the polarity information may be recovered from the average dc value of the positive and negative peaks of the polarity signal or from the coincidence of peaks of the fundamental and second harmonic components.