Abstract: The invention is a method and apparatus for performing adaptive filtering, and particularly echo cancellation, utilizing an efficient and effective adaptive algorithm. The invention is particularly useful in connection with network echo cancellation but is more broadly applicable to any situation where an adaptive estimate of a signal must be generated in real-time. The invention includes an improved proportionate normalized least mean squares algorithm for generating an impulse response estimate that is useful for generating an echo cancellation signal to be subtracted from the echo containing signal.

Abstract: Methods and apparatus for processing at least one voice signal in which a centralized voice processing unit controls operation of a plurality of voice processing block. In a first embodiment, the centralized voice processing unit comprises a centralized voice activity detector that provides at least one voice activity indication to the plurality of voice processing blocks. In a second embodiment, the centralized voice processing unit comprises a centralized noise estimator that provides at least one noise estimate to the plurality of voice processing blocks. In a third embodiment, the centralized voice processing unit comprises a centralized signal characteristic estimator that provides at least one signal characteristic estimate to the plurality of voice processing blocks.

Abstract: Methods and apparatus for compensating for the background noise modulation caused by the operation of a non-linear processor on an audio signal include a controller that receives operating status information from the non-linear processor and generates a noise reduction control signal. The methods and apparatus further include a noise reduction circuit that receives the noise reduction control signal from the controller. The noise reduction circuit reduces the background noise in the audio signal when a noise reduction control signal is generated by the controller and injects synthesized background noise into the audio signal when a noise reduction control signal is not generated by the controller.

Abstract: In a method of processing an input signal, the input signal is divided into a plurality of subbands with the aid of bank of complex valued, single-sided subband filters. The single-sided frequency spectra of the resulting subbands make aliasing negligible at near twice the critical downsampling rates.

Abstract: According to the present disclosure, a digital vehicle microphone system for recording and playback of announcements pertaining to vehicle stops and route information is provided for use over public address systems installed on public transportation vehicles. The system includes a microphone apparatus for digitally pre-recording the announcements. The microphone apparatus includes a microphone, a mute switch, a radio mode switch, a record switch and a record indicator. The system also includes a control circuit for recording and storing at least two separate announcements onto memory storage devices. The control circuit further includes a delayed playback feature for delayed playback of the announcements through the vehicle's public address system. The microphone apparatus further includes a “hands free” microphone including hand and foot actuated recording switches.

Abstract: A digital direct access arrangement (DAA) circuitry may be used to terminate the telephone connections at the user's end to provide a communication path for signals to and from the phone lines. Briefly described, a means for providing a proper ringer impedance for a variety of international phone standards while also providing a proper isolation barrier to the phone line is disclosed. More particularly, a DAA circuitry may be utilized which satisfies many or all ringer impedance standards without the use of additional discrete impedance devices. The ringer impedance standards may be satisfied by use of an impedance structure coupled between the TIP and RING lines and actively controlling the current drawn through the hookswitch devices when a ringing event is detected so as to control the impedance seen at the TIP and RING lines during a ringing event. The detection of the ringing event may be performed on the phone line side of an isolation barrier.

Abstract: Methods and apparatus for processing a transmitted voice signal include a centralized frame controller providing at least one boundary control signal to voice processing blocks and controlling the operation of the voice processing blocks on the transmitted voice signal based upon the boundary control signal.

Abstract: There is provided an audio system which suppresses standing waves. An audio signal source (1) outputs audio signals (SR) and (SL) which are then supplied to reproducing loudspeakers (3) and (4),installed in a room (2), where the reproduced sounds are outputted. Furthermore, the audio signals (SR) and (SL) are added at an adder (9) to obtain signal (S2) which is in turn filtered by a compensating filter and then inverted by means of an inverting circuit (13). This generates a compensation signal (Sc) with a phase opposite to that of the standing wave. The compensation signal (Sc) is supplied to a compensating loudspeaker (5) installed in the room (2), whereby sound for canceling out the standing wave is outputted. The compensating filter has its frequency characteristics set in accordance with the cross-correlation function between a transfer function from the reproducing loudspeakers, (3) and (4), to a listening location and a transfer function from the compensating loudspeaker (5) to the listening location.

Abstract: An exchange system minimizing ring noises generated when processing an incoming call. Upon receipt of an incoming call from a central office line, the exchange system generates a ring to a called extension telephone to which the incoming call is terminated. Thereafter, it is determined whether there is an extension telephone designating a phone number of the called extension telephone. If there is the extension telephone designating the phone number of the called extension telephone, the exchange turns on/off a lamp prepared in the extension telephone or generates a ring to the above extension telephone, after an elapse of a predetermined time.

Abstract: A microphone expander attenuates background noise in a digitized microphone signal from a wireless telephone by using a loss function that exhibits hysteresis when the signal is passing through a transition range. This allows the microphone expander to apply loss more effectively because it allows for decreases in speech levels without attenuation. An attenuation level is determined using a first loss function when an averaged signal, derived from the digitized microphone signal using an algorithm that causes the averaged signal to clearly exhibit speech components in the digitized microphone signal, increases from below a lower noise threshold. However, if the averaged signal increases to above an upper speech threshold and then decreases to below that threshold, the attenuation level is determined using a different loss function, which delays introducing loss into the microphone signal as compared to the first loss function.

Abstract: In order to quickly decrease voltage applied to a mute pin 18 of an audio amplifier circuit 19 of an electronic appliance, an end of a capacitor 20 connected to the mute pin is connected to a discharge circuit which is fired on when the electronic appliance is switched from on to off or stand-by by exploiting two power supply sources of the appliance. The voltage output of one of them decreases faster than the other one when the electronic appliance is switched off. An active element 27 of the discharge circuit has an electrode coupled to the first source and an other electrode coupled to the second sources so that the active element is fired on as soon as the difference between the two output voltages reaches a threshold.

Abstract: A bidirectional communication device for transmitting and receiving communications signals in a system which presents a transmission path for conducting a communications signal from the device, a reception path for conducting a communications signal to the device, and an echo path which conducts echo signals from the transmission path to the reception path, the device having an echo canceler connected between the transmission path and the reception path for minimizing echo signals in the transmission path, the echo canceler comprising an adaptive filter for filtering the communications signals from the device according to a filter characteristic having a plurality of filter coefficients, wherein a first group of the coefficients, constituting less than all of the coefficients, has finite filter coefficient values and the remaining ones of the plurality of coefficients have values of zero.

Abstract: A portable spa including an audio system designed to use the spa shell as the sound generating device. Transducer devices are mounted within an enclosure which is bonded to the spa shell so as to couple the sound vibration energy to the shell so that sound can be heard when using the spa.

Abstract: An electronic stethoscope including a microphone, amplifying equipment, and a loudspeaker for the user, also comprises an adjustable filter circuit. The filter circuit has a bandpass effect, and the center frequency and bandwidth of the passband can be adjusted at will throughout the audible range by the user.

Abstract: An improved service access and heat transfer design for passively cooled telecommunication repeater housings for use with wire transmission in the local loop outside plant is achieved by a cover, sealable to the housing's sidewall, removable to provide field replaceable, plug-in access to the repeater modules and voltage protector assemblies wherein the voltage protector assemblies can be installed and removed without first removing the repeater modules protected by those voltage protector assemblies and by replacing the known convection based heat transfer designs with a design based on solid thermal conduction. Thermal sleeves, which mount the repeater modules, collect the repeater modules' waste heat through thermal interfaces, transfer the waste heat along thermal conduction paths to the housing's sidewalls, and then distribute the waste heat over a substantial portion of the housing's sidewalls.

Abstract: The present disclosure describes an ultrasonically-calibrated fast-start adaptive echo canceller system. The system consists of at least one ultrasonic transducer for transmitting ultrasound signal and at least one ultrasonic receiver for receiving reflected ultrasound echo. The system also includes an echo pulse counter that operates constantly when the phone is on. The counter processes the reflected ultrasound echo from the ultrasonic receiver to determine optimum sets of ultrasonic delay and attenuation coefficients. A fast-start adaptive controller adaptively controls an algorithm stored in a random access memory to correlate sets of audio-frequency coefficients for transversal filter with predetermined sets of ultrasonic coefficients by using an ultrasound to audio-frequency conversion table. The resultant sets of audio-frequency coefficients are held on a stack.

Abstract: An enhanced near-end voice signal may be generated in a hands-free environment by receiving an audio signal, generating an estimated acoustic echo signal, and generating a processed signal by removing the estimated acoustic echo signal from the audio signal. A near-end enhanced spectrum is then determined, that has one or more ranges of contiguous frequencies over which the detector spectrum takes on its largest values, wherein the range of contiguous frequencies are those associated with a relatively high echo return loss in the processed signal. The processed signal is filtered in accordance with the near-end enhanced spectrum, thereby generating an enhanced near-end voice signal. The enhanced near-end voice signal may then be applied to any of a number of components that are intended to process near-end speech. For example, when applied to a voice activity detector, the amount of energy contained in the enhanced near-end voice signal is then measured.

Abstract: A telephone line interface circuit is disclosed that functions with use of PTC resistors so that temperature increases within the battery feed resistors is minimized. Utilizing current and voltage feedback loops within the line interface circuit, the PTC resistors are implemented without significantly reducing the performance of the overall circuit that would normally be caused by the PTC resistors' inherent impedance inaccuracies. In normal operation, the feedback loops adjust the current and voltage on the telephone line to the desired level without regard for the impedance values of the PTC resistors. In the case that a high voltage is applied to a telephone line, the significant increase in current flow into the line interface circuit causes the battery feed resistors to heat up, and therefore the PTC resistors, that are physically local to the feed resistors, to heat up and significantly increase in impedance.

Abstract: The invention relates to a circuit arrangement (1) for coupling a communication device (3) having at least one unidirectional transmission channel (4) and at least one unidirectional receive channel (5) to a bidirectional communication device having at least one differential amplifier (Q1, Q2). For optimizing the properties of the coupling by such a circuit arrangement (1) with the simplest possible means, there is proposed to couple the control inputs (C, D) of the differential amplifier (Q1, Q2) to the outputs of a transmission channel (4), its outputs (A, B) to the bidirectional communication device and the negative feedback path of the differential amplifier (Q1, Q2) to an input (E) of a receive channel (5). Its negative feedback path includes a matching impedance (R4, R5, C2) for adjusting a DC voltage/DC current characteristic (6) for the circuit arrangement (1) when connected to the bidirectional communication device.

Abstract: A method and apparatus implements a novel surround sound panning paradigm. Rather than controlling the x-y position of a perceived sound source within a linear grid, the perceived sound is characterized by specifying perceived arrival energy as a function of direction of arrival. In one embodiment, perceived sound source azimuth and width (or spatial extent) are specified, which parameters are used in a novel panning law to control each output channel. In a preferred implementation, the panning control is provided in a Plug-In application for a conventional DAW environment such as Pro Tools, which application includes an interface that provides precise control over the direction and spatial extent of audio.