Hearing device comprising a feedback detector
The application relates to a hearing device comprising a) first and second input transducers for picking up sound signals from the environment and providing first and second electric input signals, b) a first and signal strength detectors for providing signal strength estimates of the first and second electric input signal, the first input transducer being located at or behind an ear of the user, and the second input transducer being located at or in an ear canal of the user. The hearing device further comprises c) a signal processing unit providing a processed signal based on the first and second electric input signals, and d) an output unit comprising an output transducer for converting the processed signal or a signal originating therefrom to a stimulus perceivable by said user as sound. The hearing device further comprises e) a feedback detector comprising e1) a comparison unit operationally coupled to the first and second signal strength detectors and configured to compare the signal strength estimates of the first and second electric input signals and to provide a signal strength comparison measure indicative of the difference between the signal strength estimates, and e2) a decision unit for providing a feedback measure indicative of current acoustic feedback from the output transducer to the first and/or second input transducers based on the comparison measure. In an embodiment, the feedback measure is used to control processing in the signal processing unit, e.g. a beamformer unit and/or a feedback cancellation system, and/or an amplification unit. The invention may e.g. be used in hearing aids, in particular hearing aids comprising an ITE-part adapted for being located at or in an ear canal of a user and a BTE-part adapted for being located at or behind an ear or the user.
1. A hearing device adapted for being arranged at least partly on a user's head or at least partly implanted in a user's head, the hearing device comprising
an input unit for providing a multitude of electric input signals representing sound,
a signal processing unit providing a processed signal based on one or more of said multitude of electric input signals, and
an output unit comprising an output transducer for converting said processed signal or a signal originating therefrom to a stimulus perceivable by said user as sound;
the input unit comprising
a first input transducer for picking up a sound signal from the environment and providing a first electric input signal, the first input transducer being located on the head of the user;
a second input transducer for picking up a sound signal from the environment and providing a second electric input signal, the second input transducer being located at or in an ear canal of the user, the hearing device further comprising
a feedback detector comprising
a first signal strength detector for providing a signal strength estimate of the first electric input signal for each of a plurality of frequency bands, and
a second signal strength detector for providing a signal strength estimate of the second electric input signal for each of the plurality of frequency bands,
a comparison unit operationally coupled to the first and second signal strength detectors and configured to compare the signal strength estimates of the first and second electric input signals and to calculate a difference between said signal strength estimates of the first and second electric input signals as a signal strength comparison measure for each of the plurality of frequency bands;
a weighting unit comprising a mixer or a beamformer unit, the mixer or beamformer unit providing a mixed or beamformed signal based on a weighted combination of said multitude of electric input signals or signals derived therefrom,
wherein the hearing device is configured to control the weights applied by the mixer or beamformer unit on the first and second electric input signals or signals derived therefrom in dependence of the signal strength comparison measure calculated from the signal strength estimates of the first and second electric input signals for each of the plurality of frequency bands, such that the weight of the first electric input signal is increased and/or the weight of the second electric input signal is decreased in the mixed or beamformed signal in each of the plurality frequency bands in which the signal strength comparison measure indicates that the current acoustic situation is dominated by feedback.
2. A hearing device according to claim 1 comprising a BTE-part adapted to be worn at or behind an ear of a user, and an ITE-part adapted to be located at or in an ear canal of the user.
3. A hearing device according to claim 2 , wherein the first input transducer is located in the BTE-part, and wherein the second input transducer is located in the ITE-part.
4. A hearing device according to claim 1 comprising a time to time-frequency conversion unit allowing the processing of signals in the (time-) frequency domain.
5. A hearing device according to claim 1 wherein the feedback detector further comprises:
a decision unit for providing a feedback measure indicative of current acoustic feedback from said output transducer to said first and/or second input transducer based on said signal strength comparison measure for each of the plurality of frequency bands, and
wherein the hearing device is configured to control the weights applied by the mixer or beamformer unit in dependence of the feedback measure for each of the plurality of frequency bands.
6. A hearing device according to claim 5 wherein the decision unit is configured to apply a feedback difference threshold to make a binary distinction between a feedback dominant and non-feedback dominant acoustic situation.
7. A hearing device according to claim 6 wherein the feedback difference threshold is predetermined.
8. A hearing device according to claim 6 wherein the feedback difference threshold is between 5 dB and 25 dB.
9. A hearing device according to claim 1 comprising a feedback cancellation system for reducing the acoustic or mechanical feedback from the output transducer to the first and/or second input transducer, and wherein the feedback measure indicative of the amount of acoustic feedback is used to control the feedback cancellation system.
10. A hearing device according to claim 5 comprising a gain control unit, and wherein the hearing device is configured to control the gain control unit in dependence of the feedback measure.
11. A hearing device according to claim 5 comprising a configurable de-correlation unit for increasing a de-correlation between an output signal from the hearing device and an input signal to the hearing device, and wherein the hearing device is configured to control the de-correlation unit depending on the feedback measure.
12. A hearing device according to claim 11 wherein the configurable de-correlation unit is configured to introduce a frequency shift in the forward path of the hearing device.
13. A hearing device according to claim 11 configured to control the configurable de-correlation unit, including at least one of its activation, its de-activation and the amount of de-correlation depending on the feedback measure.
14. A hearing device according to claim 2 comprising three input transducers wherein two, first, input transducers are located in the BTE-part and one, second, input transducer is located in the ITE part.
15. A hearing device according to claim 1 comprising a hearing aid, a headset, an active ear protection device or a combination thereof.
16. A hearing device according to claim 1 wherein the output transducer comprises a loudspeaker for providing said stimulus as an acoustic signal to the user, and/or a vibrator for providing the stimulus as mechanical vibration of a skull bone to the user.
17. Use of a hearing device as claimed in claim 1 as a hearing aid.