Abstract: A non-invasive, non-ionizing, reproducible method and apparatus for analyzing the normal and abnormal function of human and animal joints is presented. The method includes passing vibrations through the joint to be analyzed and measuring the modulation of the amplitude and the phase characteristics of the vibrations caused by movement of the joint through a predetermined cycle. More specifically, the method includes transmitting a sinusoidal vibratory signal through a joint structure to be analyzed and measuring the amplitude and phase of the signal received on the opposite side of the joint during a prescribed movement of the joint both with and without the application of external mechanical forces, and comparing the profile of the modulated signal to the profiles obtained from reference joints.

Abstract: A volume control circuit for hearing aids is adjustable to vary a control signal supplied to an amplifier between a microphone and receiver of a hearing air. The volume control circuit includes a positive voltage source, a charge holding circuit, and a switch for alternatively connecting the holding circuit with the positive voltage source to increase its voltage, with ground to decrease voltage, and with an open circuit to maintain a constant voltage. The holding circuit voltage is inverted around a predetermined reference voltage level, with the inverted signal amplified and applied to the gate terminal of an n-channel field effect transistor having its source terminal biased to a predetermined source voltage level, and its drain terminal electrically connected to the amplifier to provide the control signal. In response to charging of the holding circuit, the gate voltage is reduced to increase the FET impedance, thus decreasing the gain of the amplifier.

Abstract: A signal processing circuit for hearing aids includes a broadband peak detector for generating a control voltage based upon the sound pressure level of an incoming acoustical signal over its entire frequency spectrum. The control signal is used to determine the cut-off frequency of a voltage controlled adaptive high-pass filter. An amplified electrical signal, corresponding to the acoustical signal, also is provided to the high-pass filter. In setting the cut-off frequency, the control voltage causes the high-pass filter to selectively suppress the low frequency portion of the signal, generating a modified signal in which the noise component is reduced.

Abstract: A miniature hearing aid unit to be fitted to and carried on a person's head; there being a directional microphone in the housing which has front and rear sound admitting openings to respectively supply sounds to the fore and aft ports of the directional microphone; the rear opening in the hearing aid housing being located significantly closer to the inner side of the housing than the forward opening so that the alignment between front and rear openings is at an oblique angle of approximately 20.degree. relative to the frontal direction.