Abstract: In a conventional stereo system, provided the listener remains equidistant from the left and right speakers, the common portions of the left and right signals produce in the mind of the listener the virtual source of sound thought to be located between the left and right speakers. In the present invention, the common components are used to power a third speaker located between the left and right speakers thereby providing a real source of sound, whereby the listener is not required to remain equidistant from the left and right speakers, but instead has considerably more latitude with respect to his position. The present invention takes the left and right signals produced by a stereo decoder, equalizes them, and develops a commonality index on which the allocation of the signals to the three speakers is based. Linear combinations of the equalized left and right signals are applied to the speakers with the coefficients each being a function only of the commonality index.

Abstract: Method and apparatus for aiding hearing are disclosed comprising an automatic gain control unit which includes a first section for increasing the amplitude of input signal segments that are below a threshold level, and a second section for reducing the amplitude of input signal segments that are above said threshold level. Both sections have short attack and long release time constants. A long attack short release time constant noise suppressor unit responsive to the output from the second section and having a threshold level of operation below that of the threshold level of the automatic gain control units passes speech signals and squelches background noise signals between speech signal segments for improved understandability of speech signals.

Abstract: A microphone picks up a signal in response to both the acoustic output of the speaker and the ambient noise at the loudspeaker location, for example, in an automobile. The microphone output signal and the signal which is to be provided to the loudspeaker with variable amplification are each subjected to envelope detection. The two envelope curve signals are compared to produce a signal representative of their similarity, the similarity being high when ambient noise is low or absent. The similarity signal is then processed with reference to a reference voltage which varies with the setting of the manual volume control of the amplifier interposed ahead of the loudspeaker. That amplifier has an automatic volume control input to which a control signal generated in response to the envelope similarity signal is applied to raise the amplification and the loudspeaker output level when ambient noise, detected by the similarity of the envelope signals, is present or increases.

Abstract: Electronic circuitry as described which enhances the intelligibility of a speech signal corrupted by low-frequency noise while tending to retain frequency components of the signal characteristic of natural-sounding speech. The circuitry includes a broad band channel which passes the speech signal with little spectral distortion. A high-pass channel produces a high-pass signal corresponding to high-frequency components of the speech signal, components which in themselves provide the human ear with considerable information for discernment of different sounds. An operational amplifier in a summing configuration combines the broadband and high-pass signals to produce a processed speech signal with enhanced intelligibility.

Abstract: An electronic volume control circuit in which the volume setting can be finely controlled, regardless of the level of the input signal, and the output sound level can be rapidly changed. A digital signal is produced indicative of either the duration of up and down instruction signals or a number of times of occurrence of the up or down instruction signals. This digital signal is decoded in accordance with a look-up table to produce data indicative of an increase or decrease width of the volume data. An arithmetic circuit operates in response to the output of the decoder to increase or decrease the volume data according to the up and down instruction signals, and the attenuation or amplification of the input signal is established accordingly.

Abstract: An improved electrically-operated backup alarm for use on mobile construction and industrial machinery, including selectable lower and higher loudness levels, automatically adjustable loudness level with respect to varying ambient noise level in which the alarm is operating, high and low frequency compensation to substantially eliminate high and low frequency signal components of the sensed ambient noise, and compensation for responding to transient signal components of the sensed ambient noise.

Abstract: An aural transmitter device is improved by largely eliminating the amplification of ambient environmental noise. To this end, control may be effected in response to the difference between a smoothed, rectified output of an amplifier and a reference voltage, either with or without a high-pass filter for removing low frequency noise components.

Abstract: An audio loudness control system for processing a broad dynamic range of audio input signals (e.g. 70 to 100 dB) comprises a gain-controlled amplifier, a feed forward control signal generator having an audio signal input that develops a feed forward gain control signal having an amplitude representative of long-term input excursions of the audio signal above a predetermined loudness threshold, a feedback control signal generator having an input from the audio output of the amplifier that develops a feedback gain control signal having an amplitude representative of transient output signal excursions above the loudness threshold, and a selector gate that selects the gain control signal of instantaneously higher effective magnitude and applies the selected gain control signal to the gain control input of the amplifier.

Abstract: A speech processor having microprocessor control of the amplitude level of input speech signals. Input speech signals are applied to a digitally controlled level regulator, the output of which is converted into a digital speech signal for further speech processing. The peak level of the digital speech signals over a frame period is compared in the microprocessor with a preset optimum range. If the peak level falls outside the optimum range, control signals for the level regulator are adjusted in a direction to change the amplification/attenuation amount of the level regulator to bring the peak level within the optimum range.

Abstract: Automatic gain control circuitry in a modem receiver, featuring a digitally controlled gain element for imposing on the received modulated carrier signal a gain corresponding to gain control signals g received from a microprocessor, an analog-to-digital converter to provide the microprocessor with digital samples of the received modulated carrier signal, and a gain control in the microprocessor for comparing an estimate of the average level of the samples with a desired level, and generating the control signals g based on the result of the comparison.

Abstract: Peak-limiting AGC for increased average power SSB transmission is improved by deriving a gain-control signal using Hilbert transform detection techniques to obtain a modulated envelope signal which is compared with a peak clipping reference to form the limiting gain-control signal.