Abstract: A system is disclosed for automatically reducing reverberation in typical voice telecommunications systems. This system uses center clipping levels adaptive to the level of reverberation input speech. In one configuration, the voiceband is divided into two sub-bands and center clipping occurs only for the lower band; costs are reduced with surprisingly little transmission quality sacrifice. Clipping-level holdover circuitry with exponential decay appears to work well for a large variety of reverberant enclosures.

Abstract: A signal is produced which is representative of the absolute value of the impedance of admittance (i.e., immittance) of a circuit as a function of frequency. At the same time, the frequencies are identified for the local maximum and minimum values of this signal.

Abstract: Equipment and methods are disclosed for testing inductively loaded telephone lines for loading irregularities. In brief, immittance magnitude measurements are used to determine the approximate frequencies of the poles and zeros of such a line and then a lossless ladder network comprising series inductors and shunt capacitors is synthesized wherein the pole and zero frequencies of the network are substantially equal to those previously determined. The network inductor values relate to the line loading inductor values while the network capacitor values relate to the distances between the loading inductors.

Abstract: Equipment and methods are disclosed for testing inductively loaded telephone lines for loading irregularities. In brief, immittance phase measurements are used to determine the approximate frequencies of the poles and zeros of such a line and then a lossless ladder network comprising series inductors and shunt capacitors is synthesized wherein the pole and zero frequencies of the network are substantially equal to those previously determined. The network inductor values relate to the line loading inductor values while the network capacitor values relate to the distances between the loading inductors.

Abstract: A controllable-gain amplifier is connected between the transmitter and receiver of a telephone set and is controlled in response to the level of the telephone user's speech so as to provide an increase in gain when the user speaks too loud and a decrease in gain when the user speaks too low. This results in a sidetone which causes the user to change his or her voice level to obtain an acceptable level of sidetone. A better-controlled user voice level is thus achieved.

Abstract: An electrical leakage path fault in the insulation of a buried conductor is located by applying, between the conductor and earth, an alternating signal which is then sensed at locations along the path of the conductor. The alternating signal is started at substantially the same phase angle at least once during each interval when it is being sensed. The sensed signal is rectified and divided by two to produce a reference signal which is phase compared with the sensed signal to trace the conductor to the fault.

Abstract: A controlled-amplitude, alternating test signal at a central office is applied to a telephone subscriber's line. The nonlinear impedance vs. voltage characteristic of the subscriber's telephone in an off-hook state causes harmonics of the test signal to be generated. A harmonic so generated is detected at the central office, which indicates the presence of a receiver-off-hook telephone.

Abstract: First and second alternating signals at a central office are applied to a telephone subscriber's lines. The level of the second signal current is used to control the level of the first signal. The nonlinear impedance vs. voltage characteristic of the subscriber's telephone in an off-hook state causes harmonics of the first signal to be generated. Harmonics so generated are detected at the central office to indicate the presence of a receiver-off-hook telephone.

Abstract: Apparatus which may be used in the performance of at least six tests on a telephone subscriber's line is disclosed. The apparatus operates to force the tip and ring leads of a line to particular potential levels and then produces output voltages related to the currents flowing in the tip and ring leads. These output voltages may be processed to perform the following test: dc Thevenin, ac three-terminal admittance, ac foreign emf, percent imbalance, swept loaded loop and detection of unauthorized equipment. The apparatus may be used when performing tests on other three-terminal circuits.

Abstract: A telephone line reported by a subscriber to be busy may be checked by the disclosed apparatus to determine if the telephone is actually in use or merely appears busy because of leakage in the telephone line or of the receiver being accidentally off-hook. When the telephone is actually in use, peaks in signals present on the line are counted and cause an in-use indication. When an accidentally off-hook or leakage condition is present, particular signals on the line or the absence of signals cause a not-in-use indication.

Abstract: A prior art antenna ass embly comprises an array of elements, a steerable beamformer for producing a desired beam and a processor interconnecting the elements and the beamformer to introduce a steerable null. Presently disclosed is a processor which broadens the steerable null while not adversely affecting its low sensitivity character. This processor includes two or more beamformers uniquely related to one another and means for substracting combinations of their outputs from the various inputs to the steerable beamformer.

Abstract: In accordance with the Hall effect, a magnetic field applied perpendicular to the direction of current flow through a conductor causes an electric field perpendicular to both the direction of the current flow and the direction of the magnetic field established in the conductor. This effect has been used to produce magnetic field and current detectors, modulators and frequency doublers. In accordance with the present disclosure a portion of the magnetic field is reversed to produce squaring of or obtaining the square root of the amplitude of the voltage used to produce the conductor current.

Abstract: Disclosed is a discrete-time filter configuration employing a shift register having output taps at only preselected stages for developing an output signal that is responsive to the signal of each stage of a shift register. The desired output signal is computed in a filter processing network by multiplying each of the output taps signals by a plurality of filter coefficients, by appropriately delaying the multiplied signals and by summing the delayed signals to produce the desired output signal.

Abstract: When two substantially identical signals contaminated by uncorrelated noise are received over two channels, combining of the contaminated signals in a linear manner results in a maximum signal-to-noise ratio improvement of 3 dB. The present disclosure relates to combining such contaminated signals through a process whose parameters vary as short time functions of the signal and noise powers in each channel. This processing produces a signal-to-noise ratio improvement which is greater than that achievable through linear processing.

Abstract: Apparatus is disclosed for selecting a preferred message signal from a plurality of received diversity message signals. Provided are autocorrelators for developing an autocorrelation function value of each received signal, and selectors for assigning as the preferred message signal the received signal having the largest autocorrelation function value.

Abstract: Disclosed is a system for synthesizing emphasis-controlled speech from stored signals representative of words precoded by a phase vocoder having analysis bands which are wide relative to the voice harmonic frequency spacings. The stored signals comprise short-time Fourier transform parameters which describe the magnitude and the phase derivative of the short-time speech spectrum. Speech emphasis-controlled synthesis is achieved by extracting the stored signals of chosen words under control of a pitch-duration signal, by concatenating the extracted signals, by modifying the magnitude parameters of the extracted signals to effect a desired speech intensity, by interpolating the extracted parameters, and by decoding the resultant signals in accordance with phase vocoder techniques.

Abstract: An electrical leakage path fault in the insulation of a buried conductor is located by first applying a composite signal comprising a test signal and a carrier signal modulated by the test signal between the conductor and earth. The two components of the composite signal are then sensed at locations along the path of the conductor. The sensed carrier signal is used by itself while its modulation content is used with the sensed test signal to trace the conductor to the fault.

Abstract: Disclosed is apparatus for automatically balancing the hybrid network in a telephone system having a bidirectional cable connected to a first preselected hybrid network port and a balancing network connected to a second preselected hybrid network port. In response to a test signal applied to a third port of the hybrid network, the disclosed apparatus develops control signals in response to the magnitude and phase of signals at the hybrid network's first and second ports. These signals adjust the impedance of the balancing network to effect hybrid network balance.

Abstract: Apparatus is disclosed for testing a cable by connecting Zener diodes or similar acting structures between terminating contacts at one end of the cable and then selectively connecting a series connected DC voltage source and resistor between terminating contacts at the other end of the cable. The diodes introduce unique voltage drops which determine the current flowing from the voltage source. The magnitude of the current is indicative of the condition of the cable with respect to continuity, correct connections, and interconductor short circuits.

Abstract: Disclosed is a system for synthesizing speech from stored signals representative of words precoded in accordance with phase vocoder techniques. The stored signals comprise short-time Fourier transform parameters which describe the magnitude and phase derivative of the short-time signal spectrum. Speech synthesis is achieved by extracting the stored signals of chosen words under control of a duration factor signal, by concatenating the extracted signals, by operating on the phase derivative parameters to effect a desired speech pitch change, by interpolating the magnitude parameters of the short-time Fourier transform in response to the pitch and duration changes, and by decoding the resultant signals in accordance with phase vocoder techniques.