Hearing aids with adaptive beamformer responsive to off-axis speech

1. A method for controlling directionality of sound reception in a hearing assistance system, comprising:

receiving sound signals including speech and noise using two or more microphones of the hearing assistance system;

determining a target direction using output of the two or more microphones;

controlling directionality of sound reception by cancelling the received sound signals that are not from the target direction;

producing an alternative signal by multiplying a rearward-looking cardioid signal with a coefficient and subtracting a signal resulting from the multiplication from a forward-looking cardioid signal;

detecting off-axis speech from the received sound signals using the alternative signal, the off-axis speech being speech that is not from the target direction; and

adjusting the directionality of sound reception by reducing the cancellation of the off-axis speech, while limiting a change to the cancellation of the noise, in response to a detection of the off-axis speech.

2. The method of claim 1 , wherein receiving the sound signals comprises receiving the sound signals using two or more microphones of one or more hearing aids.

3. The method of claim 2 , wherein receiving the sound signals comprises receiving the sound signals using two or more microphones of a hearing aid device of a mononaural hearing aid system.

4. The method of claim 2 , wherein receiving the sound signals comprises receiving the sound signals using two or more microphones of two hearing aid devices of a binaural hearing aid system.

5. The method of claim 1 , wherein detecting the off-axis speech comprises detecting the off-axis speech using output of forward-looking and rearward-looking cardioids.

6. The method of claim 1 , wherein detecting the off-axis speech comprises:

calculating a rearward signal-to-noise ratio (SNR), the rearward SNR being the SNR of a rearward-looking cardioid;

comparing the rearward SNR to a specified threshold SNR; and

indicating the detection of the off-axis speech in response to the rearward SNR being larger than the specified threshold SNR.

7. The method of claim 6 , wherein detecting the off-axis speech further comprises:

calculating a forward SNR, the forward SNR being the SNR of a forward-looking cardioid;

comparing the rearward SNR to the forward SNR; and

indicating a rear source of the off-axis speech in response to the rearward SNR exceeding the forward SNR by a specified margin.

8. A method for controlling directionality of sound reception in a hearing assistance system, comprising:

receiving sound signals using two or more microphones of the hearing assistance system;

determining a target direction of sound reception using output of the two or more microphones;

cancelling the received sound signals that are not from the target direction;

detecting off-axis speech being speech from a speech direction different from the target direction, including:

producing an alternative signal by multiplying a rearward-looking cardioid signal with a coefficient and subtracting a signal resulting from the multiplication from a forward-looking cardioid signal; and

detecting the off-axis speech using the alternative signal; and

reducing the cancellation of the received sound signals that are from the speech direction, without substantially changing the cancellation of the received sound signals that are not received from the speech direction, in response to a detection of the off-axis speech.

9. The method of claim 8 , wherein detecting the off-axis speech comprises:

calculating an alternative signal-to-noise ratio (SNR) associated with the alternative signal;

calculating a normal SNR associated with the rearward-looking cardioid signal and the forward-looking cardioid signal; and

detecting the off-axis speech using the alternative SNR and the normal SNR.

10. The method of claim 9 , wherein detecting the off-axis speech comprises:

comparing the alternative SNR to a specified threshold SNR;

comparing the alternative SNR to the normal SNR in response to the alternative SNR exceeding the specified threshold SNR; and

indicating the detection of the off-axis speech in response to the alternative SNR exceeding the normal SNR by a specified margin.

11. A hearing assistance system; comprising:

a plurality of microphones configured to receive sounds including speech and noise; and

a processor configured to:

determine a target direction using the received sounds;

control a directionality of sound reception by cancelling the received sounds that are not from the target direction;

produce an alternative signal by multiplying a rearward-looking cardioid signal with a coefficient and subtracting a signal resulting from the multiplication from a forward-looking cardioid signal;

detect off-axis speech from the received sounds using the alternative signal, the off-axis speech being speech that is not from the target direction; and

adjust the directionality of sound reception by reducing the cancellation of the off-axis speech, while substantially maintaining the noise level, in response to a detection of the off-axis speech.

12. The system of claim 11 , comprising a mononaural hearing aid system including a hearing aid devices, the hearing aid devices including the plurality of microphones and the processor.

13. The system of claim 11 , comprising a binaural hearing aid system including two hearing aid devices, the two hearing aid devices including the plurality of microphones and the processor.

14. The system of claim 11 , wherein the processor is configured to detect the off-axis speech using output of forward-looking and rearward-looking cardioids.

15. The system of claim 11 , wherein the processor is configured to:

calculate a rearward signal-to-noise ratio (SNR), the rearward SNR being the SNR of a rearward-looking cardioid; and

detect the off-axis speech using the rearward SNR.

16. The system of claim 15 , wherein the processor is configured to detect the off-axis speech using the rearward SNR and a specified threshold SNR.

17. The system of claim 16 , wherein the processor is configured to:

calculate a forward SNR, the forward SNR being the SNR of a forward-looking cardioid; and

detect the off-axis speech using the rearward SNR and the forward SNR.

18. A hearing assistance system, comprising:

a plurality of microphones configured to receive sounds; and

a processor configured to:

control a target direction of sound reception by cancelling the received sounds that are not from the target direction;

produce an alternative signal by multiplying a rearward-looking cardioid signal with a coefficient and subtracting a signal resulting from the multiplication from a forward-looking cardioid signal;

detect the off-axis speech using the alternative signal, the off-axis speech being speech from a speech direction different from the target direction; and

reduce the cancellation of the received sound signals that are from the speech direction, without substantially changing the cancellation of the received sound signals that are not received from the speech direction, in response to a detection of the off-axis speech.

19. The system of claim 18 , wherein the processor is configured to:

calculate an alternative signal-to-noise ratio (SNR) associated with the alternative signal; and

detect the off-axis speech using the alternative SNR and a specified threshold SNR.

20. The system of claim 19 , wherein the processor is configured to:

calculate a normal SNR associated with the rearward-looking cardioid signal and the forward-looking cardioid signal; and

detect the off-axis speech using the alternative SNR and the normal SNR.