Abstract: A hearing aid is fitted to a patient by first creating a filter having a frequency response dependent on the product of the frequency response of a target hearing aid and the inverse frequency response of a master hearing prosthesis that includes a microphone and an electro-acoustic transducer. The patient is then equipped with the master hearing prosthesis and the microphone of the master hearing prosthesis is exposed to an input acoustic signal, whereby the microphone generates an electrical signal. The electrical signal is processed by the filter and the filtered electrical signal is applied to the electro-acoustic transducer, whereby the patient receives an acoustic signal representative of the input acoustic signal modified by the transfer function of the filter.

Abstract: An electrical circuit system for measuring the acoustic admittance of the ear cavity, for use in single and multiple tone tympanometry and acoustic reflex response testing, in which the probe tone applied to the ear cavity can be varied over a wide frequency range and a wide range of admittance variation can be measured. The signal output of the system, derived from the output signal of a microphone located in the ear cavity, is a DC voltage accurately proportional to the logarithm of the measured admittance of the ear cavity. An RMS to DC converter, an error integrator and an exponential element provide a closed control loop system for a variable gain amplifier so as to maintain the microphone output signal level constant regardless of admittance variations in the ear cavity. The level of the signal applied to the probe tone driver to accomplish this is a measure of the cavity admittance.