Electrical audio signal processing systems and devices – Hearing aids – electrical – Noise compensation circuit
Reexamination Certificate
2002-02-06
2004-03-30
Kuntz, Curtis (Department: 2643)
Electrical audio signal processing systems and devices
Hearing aids, electrical
Noise compensation circuit
C381S322000
Reexamination Certificate
active
06714654
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
N/A
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
N/A
BACKGROUND OF THE INVENTION
The purpose of this invention is to discriminate between audio signals propagated through the air and noise signals which are propagated through the plastic shell of the hearing aid. Most of the noise transmitted through the plastic case of the hearing aid is created within the body itself; i.e. chewing, talking, walking, etc.
The present invention utilizes two microphones, both coupled to the hearing aid case, wherein one microphone is exposed to sounds propagating through the air and the second microphone is purposely sealed from sounds propagating through the air.
In a typical hearing aid, one or more microphones convert sound transmitted through the air to an electrical signal. A signal processing system (amplifiers, filters, digital filtering, etc.) processes the signal, and a loudspeaker converts the processed electrical signal back to an audio signal. The hearing aid apparatus is enclosed in a plastic case that is placed In The Ear (ITE) canal or Behind The Ear (BTH).
The microphone(s) is(are) attached to the plastic case and the case is acoustically coupled to the bone and flesh of the wearer. Therefore, any sounds that originate in the skull are conducted to the microphone(s) and amplified and echoed back to the ear.
There have been many inventions for hearing aids wherein two or more microphones are used to cancel ambient noise. Both microphones “hear” the same audio signal that is propagating through the air. The noise cancellation technique assumes that the noise source is much further distant from the two microphones as compared to the local or desired audio signal. As long as the noise is generated at a distance which is large compared to the distance between the two microphones, the signals received at each microphone will be almost equal in amplitude and phase. Then a “difference device”, for example, a differential amplifier, can subtract the two microphone signals and effectively cancel the ambient noise. In addition, two or more microphones have been used with a differential amplifier to develop a directional microphone for use on a hearing aid. However, in all cases, all of the microphones were exposed to the audio signals propagating through the air in order to produce the desired effect.
In U.S. Pat. No. 5,526,819, two microphones are used to attempt to cancel out high amplitude “body noises” (such as a cough) from the very low level desired (DPE) audio information. However, in this patent, both microphones are exposed to the same audio signals in the air. One of the microphones is designed to not respond to the DPE signals that are of a fixed and known frequency in this test. It is also “necessary” that the microphones be different. In addition, the patent does not give any information as to how the “second” microphone, which is less “sensitive” than the first microphone, cancels out high level noise signals but does not cancel out the low level DPE signal. There is some “hint” of how the second “less sensitive” microphone works, since the patent states, “The output of 30B is of less sensitivity so that the frequency components of the DPE signal are missing from the signal applied to the minus input of the differential amplifier.” In other words, the less sensitive microphone is designed to be “less sensitive” at the specific frequency that is being looked for in this patent; i.e. frequencies F1 and F2 are applied to the ear and the instrument looks for an “echo” at 2F1-F2. Also, the ratio of F2 to F1 is fixed. This patent clearly states that the typical test procedure varies F1 from 1,000 Hertz to 8,000 Hertz in steps of 100 Hertz. Therefore, the electronics must vary the frequency response of the second microphone for each step in the input frequencies.
In claim 1, lines 21 to 29, the patent states: “Said eartip including a second microphone means with a second output lead connected thereto for generating a second electrical signal on said second output lead which is proportional to said other body noises but is not substantially proportional to distortion product emission tone generated in the ear of said human being at the frequency of 2F1-F2.” This claim clearly states that the second microphone must be very frequency selective since it is specifically not substantially sensitive to a specific frequency. Again, since the patent requires that the frequencies F1 and F2 be varied over a wide range (typically 1 kHz to 8 kHz in 100 Hertz steps), this means that the frequency selectivity of the second microphone must also be varied accordingly.
In U.S. Pat. No. 6,068,589, two or more microphones are used, all exposed to free air, but placed in different positions on the body (skull) so that noise generated from a relatively large distance is coupled almost equally to both microphones and canceled out, wherein noise generated nearby is selectively coupled much greater to the closer of the two microphones and less selectively to further microphone. Therefore, the “nearby” audio signal is amplified much more than those audio signals generated at a much greater distance. This improves the signal to noise ratio since the local signal is considered the “desirable signal” as compared to the noise generated at a distance. In addition, by locating the microphones on opposite sides of the skull, it is possible to increase the “directivity” of the hearing aide. Again, all of these microphones must be exposed to all of the audio signals transmitted through the air and there is no mention of using multiple microphones to cancel noise directly coupled to the hearing aid case and generated within the body.
U.S. Pat. No. 4,622,440 also indicates the use of two microphones that are physically separated and exposed to the air in order to “hear” the audio signals transmitted through the air. As in the previous patents, this patent subtracts the audio signals generated in each microphone in order to cancel noise generated at a “distance” that is large compared to the physical space between the two microphones. If this “distance” is relatively large compared to the physical separation of the two microphones, than the signals received by the two microphones will be substantially equal in amplitude and phase and may be canceled using a differential amplifier.
Audio signals generated much closer to the two microphones will be coupled greater to one microphone than the other and will not be completely canceled. In this type of circuit, both microphones are exposed to air in order to cancel noise generated at a distance. This type of circuit can also be used to enhance the “directivity” of a microphone.
U.S. Pat. No. 5,757,933 is almost identical to U.S. Pat. No. 4,622,440 except that this patent includes the use of a switch to either add the signals of the two microphones together or to subtract the signals from the two microphones. By varying the phase and gain of one microphone versus the other, the microphones can be made somewhat “directional”. Both microphones must be exposed to the air.
U.S. Pat. No. 5,402,496 again discusses the use of two microphones, both exposed to hear the audio signals transmitted through the air. The output of one microphone passes through a “first filter”. To quote: “The first filter generates a reference signal by selectively passing an audio spectrum of the input signal which primarily contains the undesired component.” This statement alone says that one must first “know” what the “undesired component” (i.e. noise) is, which is not useful in situations in which it is not possible to “know” in advance what the noise is. In addition, in this patent, both microphones are not identical.
Also, according to this invention, only one microphone is actually required. The output from this microphone is passed through a “first” filter as well as directly to the remainder of the signal processing electronics. There appears to be no explicit mention of a “second” microphone in the claims.
EP 0 782 371 B1 refers to the des
Ensey Brian
Kuntz Curtis
Weingarten Schurgin, Gagnebin & Lebovici LLP
LandOfFree
Hearing aid operative to cancel sounds propagating through... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hearing aid operative to cancel sounds propagating through..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hearing aid operative to cancel sounds propagating through... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3216459