Abstract: A compact speakerphone apparatus is provided with an angled housing for a speaker and a directional microphone. The speaker and microphone are mounted in the housing such that the directional characteristics of the microphone minimizes feedback from the speaker. Additionally, the speaker is mounted to direct sounds away from a horizontal surface upon which the speakerphone may be placed in a just configuration. In a second configuration, the speaker may be mounted upon an elevating bracket for suspending the speaker at a rotated position whereby the directional microphone remains oriented toward a user's mouth.

Abstract: A speech detection system is provided with multiple speech detector sub-systems. The speech detection sub-systems employ distinct statistical methods for determining whether speech is present in an electronic communication signal received at an output terminal. For example, a first speech detection sub-system employs moving average peak signal filter, a second speech detection sub-system employing a moving average noise filter, and a third speech detection sub-system employs a variance filter. Signals from each of the filters are compared with respective threshold values, and the threshold values are provided to speech determination logic for making an aggregate speech detection decision. The speech detection system is useful for telephonic automatic gain control.

Abstract: A system for monitoring and managing the operations of a multi-technology telecommunications network is disclosed. The system includes programmable probes operatively connected to a network for monitoring data transfer activity on the network and collecting selected data relating to one or more relevant functions. A workstation interpreter is programmed for (1) receiving input from a system manager identifying the type or types of parameters that are to be monitored, (2) providing appropriate commands to program the programmable probe to effect collection of data relative to the selected parameter, and (3) receiving and storing the parameter data from the probe. The probe hardware is selected for compatibility with the network technology with which it is associated and it is programmed with the appropriate protocols to facilitate communications with the associated technology.

Abstract: An apparatus is provided for digital signal processing of telecommunication signals along respective transmit and receive paths of a two-way telecommunication link. The respective transmit and receive signals each include an audio data component and a timing component. Digital signal processing of at least one of the signals, such as an echo cancellation, employs information derived from the audio data component of the other signal. To compensate for differences between the respective timing components of the signals, resynchronization of each signal in terms of the timing component of the other signal is performed prior to modifying the audio data component of the other signal.

Abstract: A telecommunication signal processor includes a noise compensation system for preventing undesirable spectral modulation of the noise component of a telecommunication signal subjected to a process wherein subband portions of the signal are variably attenuated. A noise component is injected into each attenuated error signal in order to compensate for attenuation of background noise incidental to the variable attenuation of the subband signals. The amplitude of the noise components are each determined independently on the basis of an estimated noise content of the original subband signals and in accordance with the applied attenuation within each subband. The attenuated and noise-compensated subband signals are combined by a synthesis filter to provide a send-output signal.

Abstract: An echo canceler is connected to an ISDN Primary Rate Interface. The echo canceler is provided with an activation processor for monitoring call control messages on the D-channel and for selectively enabling or disabling echo cancellation on any of the B-channels in response to information contained within the call control messages. In particular, the activation processor decides whether to enable cancellation depending upon the Information Transfer Capability and Protocol Identification fields of the Bearer Capability portion of a call SETUP message. Additionally, the Channel Identification field of the SETUP message is used to identify the B-channel or channels affected by the SETUP message. When a channel is released, the activation processor maintains enabled echo cancellation as the default condition of the released channel. Other signal processing functions can be controlled by the activation processor in a similar manner.

Abstract: An echo canceler for canceling echo components of a send-input signal, includes an analysis filter bank for dividing the send-input signal into a plurality of subband send-input signals. A receive-signal is also divided into a plurality of subband receive signals. Each of the subband receive signals is convolved with an impulse response function pertaining the echo path coupling the receive signal to the send-input signal within each subband. The convolutions yield a plurality of estimated echo signals, which are then each subtracted from the corresponding subband send-input signal, to produce a plurality of error signals. Residual echo components within the error signals are attenuated by a variable attenuator in response to a comparison of relative levels of corresponding subband send-input Signals, subband receive signals and the error signals.

Abstract: An adapter for interconnecting a tip-ring telephone, a PBX telephone, and a private branch exchange (PBX) is configured to pass out-of-band signals between the PBX telephone and the PBX and to attenuate voice-band signals therebetween when the tip-ring telephone is being used. The adapter includes a band-reject filter and a switching mechanism for connecting the band-reject filter between the PBX telephone and the tip-ring telephone.

Abstract: A digitally programmable attenuator balances impedance across a two to four-wire hybrid to reduce echo. The hybrid can interface a two-wire bi-directional telephone line, used for both transmit and receive signals with four-wire circuits having separate unidirectional transmit and receive signal paths. The four-wire circuit interfaces the two-wire circuit through a transformer. Optimum isolation is obtained by setting impedance Z.sub.BAL equal to the impedance of the line including the transformer (Z.sub.LINE). The invention eliminates manual or customized individual adjustment of Z.sub.BAL by a set up technician by use of a digitally controlled attenuator to electronically vary the value of Z.sub.BAL in a highly precise fashion. The programmable attenuator provides an input voltage to a buffer voltage-follower amplifier. The output of the follower amplifier is coupled to a known impedance to limit current flow through the impedance and consequently, current flow through Z.sub.BAL.

Abstract: First and second ISDN modems are disposed at a subscriber location and telephone system central office and are arranged to operate in a normal mode, and in a bypass mode upon power failure at the subscriber location. The modems are coupled through the telephone lines via interface transformers having centertaps. The centertap at the subscriber location is split and coupled to a sealing current source and that at the central office is coupled to a sealing current detector and ground. Sealing current flows between the respective transformers during normal operation. A drop in sealing current due to subscriber power failure is sensed at the central office, causing local logic to bypass the central office interface transformer and to couple the central office voice switch directly to the telephone lines. Loop current detectors at the subscriber location and at the central office determine whether the subscriber location voice telephone device is on-hook.

Abstract: An echo canceller with an adaptive convolution processor for computing and subtracting an anticipated echo has a nonlinear processor coupled to the error signal and to the send output. The nonlinear processor is responsive to average values and attenuates the error signal over a continuous range as a function of presence of send and receive signals, rather than coupling and decoupling the error signal to the output in the manner of a center clipper. Attenuation is altered rapidly when one of the send and receive ends is active, which may be detected by their averages or by loss across a summing junction providing the error signal. Attenuation is decreased gradually neither of the send and receive ends are active. The error signal attenuation level is also used to control injection of artificial noise.

Abstract: A clock generator for extracting a clock signal from a data signal includes a timing recovery circuit operable to produce an output recovered clock which is synchronized with transitions occurring at its input. A circuit gates data transitions to the clock recovery circuit input only during time windows defined in a manner based upon the recovered clock. The time windows are produced by comparing the output of an integrator on the recovered clock signal to a reference. The comparator output resets a D-flip flop, to which the data is applied as a clock, the output of the D-flip flop being connected to the input of the timing recovery circuit.

Abstract: A time division multiplexer is operable to sample data on parallel input channels at a sampling rate at least twice the data rate, to serially transmit the data for each channel in a respective time division, and to recover the data at a receive end. The multiplexer is provided with a bit storage register for successive samples on at least one input channel to be used as a marker channel. Gating connected to the bit storage register forces a detectable unnatural data pattern on the transmitted data for that channel whenever a predetermined bit pattern is stored for that channel. According to one embodiment, when a plurality of unchanged levels (e.g., binary one) appear in the bit storage register, a central bit is inverted to thereby mark that channel. The inverted marker bit is detected and cancelled at the receive end and/or is used to reset the channel counter if detected on a channel other than the marker channel.