Abstract: An echo cancellation device usable in telephone connections affected by phase-roll is described. The canceller calculates the echo path propagation delay and produces an estimate of the echo signal by digitally filtering the signal originated by the far-end talker. The echo estimate is then subtracted from the actual echo to eliminate listening disturbances. The filter used is of the FIR type with adaptive coefficients updated iteratively by adding algebraically, to the values which they had upon the preceding iteration, a correction term proportional to the estimate error. The frequency of the coefficient updating iterations is a multiple of the rate f.sub.c of acquisition of the voice and echo samples by the canceller.

Abstract: A telephone handset outbound noise canceller uses an omnidirectional reference microphone placed near the transmitter grille. Two adaptive filters are employed, one driven by the handset transmitter to subtract speech from a reference value to produce an enhanced reference signal; and a second adaptive filter driven by the enhanced reference signal to subtract noise from the transmitter. The weights of the two adaptive filters are allowed to adapt or are frozen according to criteria set as a result of transmitter power measurements which determine whether speech is likely to be present or not.

Abstract: A telephone visual signaling device is provided which consists of a telephone connected to an incoming signal line and a mechanism for producing an identifiable beam of light when the telephone receives a telephone call on the incoming signal line.

Abstract: Disclosed are hands-free land-line and radio telephones comprising a public telecommunication network connection part for transmitting a signal from the transmission signal input terminal to the public telecommunication network connection terminal and a reception signal from the public telecommunication network connection terminal to the reception signal output terminal, a first voltage controlled attenuator for controlling an output of the microphone by a given loss corresponding to a first control voltage level, a second voltage controlled attenuator for controlling a reception signal by a given loss corresponding to a second control voltage input level, a first detection circuit for generating a rectified voltage proportional to a magnitude of an input audio signal by rectifying an output signal of the microphone, a second detection circuit for generating a rectified voltage proportional to a magnitude of an input audio signal by rectifying an output signal of the reception signal output terminal, a contro

Abstract: Echo canceling method and apparatus for subtracting, from a mixed signal in which echoes produced from a plurality of reception signals are mixed with a transmission signal, a replica of the echoes in order to cancel the echoes in the mixed signal. The replica of the echoes are generated by the steps of selecting the reception signal which is leading in phase and producing a replica of the echoes from the selected reception signal by an adaptive filter. Generally, the replicas are produced by adaptive filters provided in one-to-one correspondence with the mixed signals.

Abstract: Disclosed is a circuit for providing an appropriate amount of on-hook loss in a digital loop carder transmission system serving telephone customers. The resistance of the customer loop is measured while the customer is off-hook and an amount of loss is added based on that resistance during the off-hook interval. A predetermined constant loss is then added to the appropriate off-hook loss when the equipment returns to on-hook status.

Abstract: A modem's data reception rate is increased by decreasing the amplitude of the signals transmitted by the modem. Decreasing the amplitude of the transmitted signals reduces the amplitude of the resulting echoes, and thereby reduces the residual echoes that remain after echo cancellation. Reducing the residual echoes permits increasing the data reception rate. Decreasing the amplitude of the transmitted signals also involves decreasing the data transmission rate; however, asymmetrical data transfer rates are acceptable for many modem applications.

Abstract: A parallel phone detection circuit is described, the function of which is to enable a phone call to be transferred from a first telephone set to a second telephone set. The detection circuit maintains the first telephone set connected to the telephone line until the handset of the second telephone set has been taken off-hook, and then disconnects the first telephone set. The circuit operates by detecting the line current from the telephone line and produces the reference value for comparison purposes related to that line current.

Abstract: A method of dual-tone multifrequency (DTMF) detection which decimates and adaptively filters an input signal is provided to efficiently detect a presence of a DTMF signal. The input signal is provided to a half-band filter (14) to be decimated in frequency in accordance with Nyquist's theory. A decimated input signal is subsequently processed to form a low frequency component signal and a high frequency component signal. The low frequency component signal is again decimated by a decimator (24). The decimated low frequency component signal and the high frequency component signal are each filtered by an adaptive fir filter (22, 26) to provide a first and a second frequency parameter and a first and a second gain factor, respectively. The first and second frequency parameters and the first and second gain factors are then tested by a tone identifier (28) to determine if the input signal includes a valid DTMF signal.

Abstract: An echo canceller for use in send/receive apparatus includes a frequency-domain adaptive filter which provides filter parameters to a time-domain programmable filter. The programmable filter produces a signal y(k) which is an estimate of the echo signal produced by acoustic coupling between a loudspeaker in the received path and a microphone in the send path. By subtracting this estimate from the signal produced in the send path, an output signal r(k) is obtained from the send path which is essentially free of echoes. An accurate estimate of the echo signal cannot be obtained if a send signal is present at the input of the send path. Therefore, detecting means in the adaptive filter detects whether such a send signal is present and in that case blocks the transfer of filter parameters from the adaptive filter to the programmable filter. Erroneous modification of the estimated echo signal is thereby avoided.

Abstract: A common mode noise removing apparatus connected to connection lines between switching networks, for a loop dial relay line, includes a direct current power source for applying a predetermined direct current voltage to the connection lines, a reverse flow preventing unit connected between the direct current power source and the connection lines, a power supply control supervision unit for supervising the power supply condition of the loop current which flows in a loop, and a short-circuit unit for short-circuiting the reverse flow preventing unit in a mode in which no dial pulse is received by the apparatus from another such apparatus and the power supply control supervision unit detects the loop current.

Abstract: Apparatus for reducing acoustic background noise for use with a telephone handset or a boom microphone device or the like. The apparatus includes first and second microphones which are arranged such that the first microphone receives a desired speech input and the background noise present in the vicinity of the speech, and the second microphone receives substantially only the background noise. The background noise from the second microphone is converted into a corresponding electrical signal and subtracted from a signal corresponding to the speech and background noise obtained from the first microphone so as to produce a signal representing substantially the speech.

Abstract: A telephone circuit is provided for distinguishing between a normal incoming telephone call and a test telephone call. When the telephone is polled from a central station to cause it to undergo a self-test routine, a ringing signal is used which consists of a series of three ringing signals each lasting less than a predetermined time. Consequently, when such a ringing signal is received, a relay remains open so that there is no audible ringing tone. The system thus enables a testing routine to be carried out by the telephone without causing the telephone to ring.

Abstract: A network interface module for providing connection between a customer's equipment and the telephone company owned portion of the customer loop is provided with a miniaturized easily removable module which includes the overvoltage protection device and the circuitry necessary to provide a prescribed line test termination impedance having a particular characteristic signature to the telephone central office when a continuity test is made on a subscriber line.

Abstract: Distortion and instability due to echoes in conference communications is reduced through the use of an echo estimating filter disposed in a conference bridging circuit. This circuit includes a signal combiner which receives information signals from each of the parties in the conference communications and provides an output signal which is a combination of the received information signals and an echo compensation signal. The echo estimating filter provides this echo compensation signal in response to the combiner output signal. Advantageously, the echo estimating filter can be fixed or adaptive. In the latter case, the adaptation can be in response to the received information signals or to training sequences.

Abstract: A double echo cancelling system includes comparators which monitor, respectively, "unmodified" signals from the near end or far end and "modified" signals from the other end. The unmodified signals are the signals received by the system and the modified signals are those signals which have been subjected to echo cancellation and attenuation. A comparator determines that a caller at one end is speaking if the associated unmodified signals exceed by more than a predetermined value the modified signals associated with the other end. The comparator which detects near end speech controls the adaptation of an associated adaptive filter and the operation of a cancellation monitor, which, in turn, controls the adaptation of the adaptive filter associated with the far end. When this comparator detects near end speech, it enables the cancellation monitor.

Abstract: A method and apparatus for detecting and classifying signals that are the additive combination of a few constant-amplitude sinusoidal components, herein called N-tones. The attributes of this method and apparatus include provision of superior classification performance with an algorithm of low computational complexity. The method includes filtering to remove extraneous signal components, separation of the incoming signal into one or more output streams and segmenting these output streams into blocks of successive data samples. The magnitude of the data within each block is estimated along with the frequencies of the dominant spectral components. The frequency estimates are then used as part of the configuration process of a set of notch filters for removal of the identified dominant spectral components. The newly-configured notch filters are then applied to the same data blocks and the magnitudes of their outputs are estimated.

Abstract: An amplifier for amplifying a signal received on a telephone line and for providing the amplified signal to a telephone headset. The amplifier draws current from a battery. The current drawn is reduced in the absence of activity on the line. The amplifier includes a timer that generates a first control signal after a time-out time. The timer is reset by a second control signal. A threshold circuit generates the second control signal when the signal on the telephone line is above a threshold level. Finally, a circuit, responsive to the first control signal, reduces the current drawn from the power supply. The amplifier may additionally or alternatively include receive line muting. The amplifier includes an automatic level control circuit that receives the signal received on the telephone line and controls the level of the amplified signal provided to the headset to a set level in response to a second control signal.

Abstract: A battery feed circuit supplies a feed current to a telephone set via a 2-wire telecommunication line formed of a TIP line and a RING line.

Abstract: A system and method for controlling the dialing order of a plurality of call record lists by a predictive dialing system are disclosed. The system includes a flow controller and a list controller. The list controller receives a number of call records from a call list provider for establishing a plurality of call record lists. The flow controller links one or more call lists in a predetermined order to form one or more list flow campaigns which may be later edited or joined together by the flow controller. A predictive dialer receives the call lists according to the list flow campaign and dials telephone numbers in the order directed by the linked call record lists which form the flow campaign. Also disclosed is a method for linking call record lists.