Abstract: Techniques for reducing unwanted acoustic feedback in a space are carried out by an adaptive notch filter algorithm that adjusts a notch to a plurality of different notch values in order to locate feedback. The results obtained by performing the algorithm at various notch values are compared. Based on the comparison, the parameters for the algorithm are adjusted for processing of the input signals to reduce the feedback.

Abstract: A method and apparatus for determining the status of a battery that powers a wireless microphone transmitter. The transmitter has a tone oscillator that produces a tone of a frequency beyond the audible limit which is transmitted, along with acoustical signals, to a receiver. The amplitude of the tone is changed as the battery voltage of the transmitter decreases. The receiver for the transmitter includes a circuit that detects the changes in amplitude of the high frequency tone. The front panel of the receiver, for example, may contain an LCD display on which a battery fuel gauge is present, indicating the remaining battery life of transmitter. When an amplitude change beyond a threshold is detected, the fuel gauge is updated, and the respective bar on the gauge is turned off.

Abstract: A microphone for reducing distortion of an audio signal due to wind or plosive sounds emitted by a user, including a microphone cartridge defining a central axis and a cylinder contiguous with the perimeter of the cartridge. A windscreen defines first, second and third acoustical paths. The first and second paths are through the side of the windscreen and the third path is along the axis of the windscreen. The third path has an acoustical resistance greater than the first or second paths. The second path has an acoustical resistance greater than the first path.

Abstract: An improved automatic microphone actuation control system. The system exhibits a high degree of resistance to inappropriate secondary microphone actuation by reverberant sound, even when two or more microphones in a system are operated at significantly different electroacoustic gains. The system further exhibits improved actuation sensitivity to local conference room speech occurring simultaneously with teleconference loudspeaker sound which is strongly coupled acoustically to the microphones. A Reverb Inhibit Bus, which is the maximum of a reduced level speaker inhibit signal and substantially attenuated versions of the DC microphone signal level representations, drives the microphone channels' noise adapting threshold circuitry. Such circuitry is driven in a manner to inhibit microphone actuation for teleconference loudspeaker sound reverberation and reverberation of local conference room speech which has already actuated a microphone.

Abstract: A bi-directional noise-cancelling microphone comprising a detector for detecting acoustical signals centrally positioned within a tubular member that has flared entries. The microphone provides a bi-polar response pattern, and effectively cancels unwanted noise incident upon the microphone at the sides of the tubular member, as well as noise above a particular frequency dictated by the length of the tubular member. By providing flared entries to the tube, the maximum peak response frequency of the microphone is extended up to 40% higher than that achieved with a similar tubular member with non-flared entries. An embodiment of the tubular bi-directional microphone with flared entries is disclosed wherein the microphone is provided with a two-stage pop filter system. The pop filter system includes a first screen covering the front entry of the microphone housing. A second screen is constructed so as to vent the first screen, thereby preventing pop signals from being produced.

Abstract: An echo reduction circuit that may be used to reduce the returned echo in communication links with signficant delay. By making effective use of the echo-masking effect of near-simultaneous desired speech energy and the redundancy present in normal speech, the circuit makes possible wide bandwidth, non-choppy, perceived distortion-free, and perceived echo-free teleconferencing. The circuit performs a rapid time constant, semi-waveform-following partial attenuation of a preemphasized version of the returning transmit signal proportional to a calculation of the likely strength of the returned echo in relation to the strength of the local speech.

Abstract: An adaptive delta modulation circuit having an analog adaptation circuit and an integrator circuit. The adaptation circuit exponentially converts a voltage which is proportional to the average of a time duration of an overload control signal to an adaptation current which is averaged and converted to an adaptation voltage. An integrator circuit includes a sole switch which shorts to ground a circuit point for generating an analog signal formed of line segments; each segment has a slope magnitude controllable by the adaptation voltage.

Abstract: A loudspeaker horn, which is divided into three segments, is provided with a valve for projecting sound either through the central segment or through all of the segments, said valve being adjustable from the front of the loudspeaker by a knob which has markings thereon to indicate the position of the valve and which is provided with means for retaining it in the position set by the knob.

Abstract: A magnetic stereo phonograph pick-up cartridge is disclosed. An elongated stylus and an attached permanent magnet are resiliently supported by a molded rubber bearing block which surrounds the magnet and engages under compression with the inner side-walls of a stylus housing sleeve. The molded block is shaped to also serve as a cantilevered inertial damping member which is held in mechanical contact with the magnet. The bearing portion of the block is fabricated from a first material exhibiting high compliance and the inertial damping portion of the block is fabricated from a second material exhibiting high damping characteristics, especially in the high audio frequency range.

Abstract: A line level microphone. The microphone includes an amplifier and a peak limiter variably shunting the input of the amplifier to substantially avoid distortion or clipping of the microphone output signal.