Abstract: A frequency selective hearing protection device and method utilizes adaptive filtering to hinder transmission of frequency components in ambient sound above a preselected threshold level. Sound frequency components which are not above the threshold level, such as normal speech, are allowed to pass. Electrical analog signals produced by a transducer are converted to a stream of digital input signals. The digital input signals are applied to a digital filter such as an FIR filter implementing a time domain difference equation. As a result, digital output signals are produced which are reconverted to analog output signals and applied to an actuator to produce audible sound. To adjust the frequency response of the invention to suppress gain at frequency components above the threshold, windows of input and output data signals are first assembled. Respective frequency domain transforms such as fast Fourier transforms provide spectrums representative of frequency component amplitudes.

Abstract: A car stereo has a detachable grille attached to a body of the car stereo. A display is provided on the car stereo body for display operating modes of the car stereo. A cover is provided on the car stereo body for covering the display when the grille is detached. The cover is moved to a retracted position so as to expose the display when the grille is attached to the body.

Abstract: An apparatus for reducing noise for an interior of enclosed space, e.g., a vehicular compartment using an FIR adaptive digital filter is disclosed in which a control circuit is provided which outputs drive signals to a plurality of loud speakers which generate control sounds to interfer with a noise sound propagated in the interior so that a performance function including terms of residual noise signals output from residual noise signal detecting microphones and drive signals to the loud speakers is minimized and contributivity of the drive signals to the performance function is changed according to an occurrence of divergence in the noise reducing apparatus.

Abstract: A data input/output circuit of a digital signal processor of the invention includes a converter circuit for serial-parallel conversion of data, an R-channel dedicated input latch circuit, two L-channel dedicated input latch circuits, an L-channel dedicated output latch circuit, an R-channel dedicated output data latch circuit, a multiplexer for switching output data, an edge detection circuit, a rising edge detection circuit, and a falling edge detecting circuit. The circuits 14, 14a and 14b supply latch or switching timing signals to the above circuits. Thus, the R-channel data and L-channel data can be transferred to other functional blocks through an internal bus during one sampling period. Thus, the right channel data and the left channel data are processed simultaneously, so that the signal processing time can be made unrelated to the input/output data.

Abstract: A combination headband and stereo earphones having two elongated strips of material releasably attached to each other. The ends of the strips can be attached to form a headband. The wires attached to each earphone are placed in the headband and maintained in place when the strips of the headband are attached to each other. The strips can be imprinted with names, logos and designs for promotional and sponsorship advertising.

Abstract: The housings of the devices are divided by inner walls into two or three inner chambers. One of the inner chambers adjoins the membrane of the loudspeaker. Adjoining this inner chamber a membrane is built into an opening of an inner wall. Movements of the inner membrane, which are caused by pressure changes in this chamber, are servo supported by an inner electrodynamic transducer, whose membrane lies parallel behind the other inner membrane. The supporting movements are caused by a controller, which tries to hold constant the distance between the two inner membranes.

Abstract: A sound field offset device having two channels, each of which includes a frequency selection filter for dividing a stereophonic input signal into two frequency bands by a given frequency falling within an audio frequency, at least one digital filter for performing sound field offsetting within a lower frequency band, and at least one loudspeaker assembly for a higher frequency band having a sharp directivity pattern and capable of defining an area to which acoustic power is emitted. This device allows a sound field to be offset in a cost effective and simple manner, by improving the frequency characteristic of a sound field space and by clarifying the sense of locality of acoustic images.

Abstract: Instrumentation for determining audio phase polarity is directed particularly to avoiding errors commonly encountered in pulsed acoustic polarity testing due to waveform distortions such as overshoot and ringing typically introduced by loudspeaker cone resonances, etc. The acoustic signal is sensed by a test microphone, amplified and processed to provide a non-inverted and an inverted waveform which are envelope-detected and their leading edges analyzed in real time at three key levels. One of pair of latching comparators triggers at a designated level to determine the phase polarity. The result is held in register while the signal amplitude is checked. If the amplitude is found to be within a suitable working dynamic range then the registered phase polarity is indicated by a timed indication on either a red or a green LED; otherwise indication is inhibited to avoid error. Thus a user sensitivity control is not required.

Abstract: An active sound reproducer (76, 78) receives an audio signal and setting signals (volume settings, filter coefficients) via a digital bus (75) for processing the audio signal. Normally, the setting signals are applied by a suitable ("compatible") control unit (74). If this unit is not present, this task is taken over by one sound reproducer operating as a "master". In a setup procedure, it is determined which one of the sound reproducers operates as a master. Each sound reproducer is adapted to receive remote control signals and to transmit these signals to the master reproducer via the digital bus. This master reproducer then distributes the setting signals to the relevant sound reproducers via the digital bus. The control unit or the reproducer operating as a master may be located in another space.

Abstract: A first monophonic signal within a predetermined frequency range and a second monophonic signal at least outside of the predetermined frequency range are produced from a monophonic input signal. A simulated-stereo device is provided for dividing each of the first and second monophonic signals into stereo-simulated signals. The level of the first monophonic signal is compared with the level of the second monophonic signal. The level of the first stereo-simulated signal is attenuated when the level of the first monophonic signal is higher than the level of the outside monophonic signal.

Abstract: In a system in which a low-bit rate encoder and decoder carries matrixed audio signals, an adaptive rematrix rematrixes matrixed signals from an unmodified 4:2 matrix encoder to separate and isolate quiet components from loud ones, thereby avoiding the corruption of quiet signals with the low-bit-rate coding quantization noise of loud signals. The decoder is similarly equipped with a rematrix, which tracks the encoder rematrix and restores the signals to the form required by the unmodified 2:4 matrix decoder. The encoder adaptive rematrix selects the matrix output signals or the amplitude weighted sum and difference of the matrix output signals. The choice of whether the matrix output signals or the sum and difference of the matrix output signals are selected is based on a determination of which results in fewer undesirable artifacts when the output audio signals are recovered in the decoder.

Abstract: A sub-woofer arrangement for the reproduction of bass tones is provided in an armrest of a seat of a passenger car. The sub-woofer arrangement has a sound outlet orifice positioned so as to face a dashboard when lowered in a first position and be unobstructed when raised into a second position in a recess within the seat.

Abstract: An arcuate speaker is arranged for pivotal mounting relative to a vehicular rear shelf plate in operative communication with a cover plate, wherein pivoting of the speaker in communication with a bottom surface of the rear shelf plate effects pivotal displacement of the cover plate for audible access of the speaker relative to an associated passenger compartment of the vehicle.

Abstract: Left right and surround components of a stereo signal are coded into a monaural and small co-channel providing volume steering for recreating a stereo effect with a substantially reduced bit rate. The signal is split into a sum and difference signal, the difference signal is randomized and the sum is added to the randomized difference to comprise the single audio channel. A functional relationship is solved for left and right volumes which is then transmitted for intervals on the co-channel. Decoding of the single transmission channel directs it to left, right, or surround channels based on decoding on the logic co-channel. The co-channel updates left and right volume levels which are interpolated through time to effect smooth volume change. Surround gain is determined from left and right channel gains to maintain unity total volume, with the sum of the squares of the three volume controls being unity.