Noise reduction circuit for hearing aid
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.
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.