Noise reduction circuit for hearing aid

Abstract

Noise reduction circuitry in a hearing aid includes a programmable filter coupled to a microphone coupled to the ear canal. The filter is programmed in a feedback loop in which the coefficients of the filter are set in accordance with a signal from the microphone. The filter is programmed for a transfer function that is substantially the inverse of the spectrum of the sound detected by the microphone to provide a relatively quiet chamber in the ear canal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:

FIG. 1 is a sectional view of a hearing aid constructed in accordance with a preferred embodiment of the invention installed in a human ear canal;

FIG. 2 is block diagram of signal processing circuitry within the hearing aid illustrated in FIG. 1;

FIG. 3 is a diagram for explaining the operation of the filter in FIG. 2;

FIG. 4 is a perspective view of a behind the ear hearing aid constructed in accordance with the invention; and

FIG. 6 is block diagram of an alternative embodiment of signal processing circuitry within the hearing aid illustrated in FIG. 1.

Claims

1. In a hearing aid having an external microphone, an internal microphone, and a speaker, the improvement comprising: noise reduction circuitry including a programmable filter coupled to said external microphone, wherein the coefficients of the programmable filter are set in accordance with a signal from said internal microphone;whereby the signal picked up by the internal microphone is minimized.

2. The hearing aid as set forth in claim 1 wherein said hearing aid is an in-the-ear-canal type of hearing aid.

3. The hearing aid as set forth in claim 1 wherein said hearing aid is an behind-the-ear type of hearing aid.

4. The hearing aid as set forth in claim 3 wherein said hearing aid is coupled to the ear canal by a first conductor coupled to said internal microphone and a second conductor coupled to said speaker.

5. The hearing aid as set forth in claim 1 wherein said filter is programmed for a transfer function that is substantially the inverse of the spectrum of the sound picked up by said internal microphone.

6. The hearing aid as set forth in claim 1 and further including a multiplier having a first input coupled to said internal microphone and a second input coupled to said speaker, wherein the coefficients of the programmable filter are set in accordance with a signal from said multiplier.