Method and apparatus for suppressing transient sounds in hearing assistance devices
An audio system includes a transient suppression circuit that rectifies an input signal representing target sounds and transient sounds and produces a threshold envelope of the rectified input signal. The transient suppression circuit accumulates the difference between the rectified input signal and the threshold envelope, and normalizes the accumulated difference using the rectified input signal. A gain is calculated using this normalized accumulated difference and applied to the input signal to suppress the transient sounds without substantially affecting the target sounds.
1. A hearing aid for use by a listener, comprising:
a microphone;
a processing circuit configured to receive an input signal from the microphone, filter the input signal, rectify the filtered input signal, generate an envelope of the rectified input signal, accumulate a difference between the rectified input signal and the envelope, determine an applied gain based on the accumulated difference, and produce an output signal by applying the applied gain to the input signal in frequency domain; and
a speaker configured to receive the output signal from the processing circuit and produce output sounds based on the output signal, wherein the hearing aid is configured to be worn by the listener to compensate for hearing loss of the listener.
2. The hearing aid of claim 1 , wherein the processing circuit is further configured to decimate the input signal before the rectification of the input signal.
3. The hearing aid of claim 2 , wherein the processing circuit is further configured to normalize the accumulated difference using the rectified input signal.
4. The hearing aid of claim 3 , wherein the processing circuit is further configured to calculate a target gain using the normalized accumulated difference and determine the applied gain based on the target gain.
5. The hearing aid of claim 4 , wherein the processing circuit is further configured to scale the envelope by multiplying the envelope by a threshold shift before the accumulation of the difference.
6. The hearing aid of claim 4 , wherein the processing circuit is configured to calculate the target gain by subtracting the normalized accumulator value from 1.
7. The hearing aid of claim 6 , wherein the processing circuit is configured to set the target gain to a minimum target gain value when the calculated target gain is less than the minimum target gain.
8. The hearing aid of claim 7 , wherein the processing circuit is configured to set the applied gain to the target gain when the applied gain is greater than the target gain.
9. The hearing aid of claim 8 , wherein the processing circuit is configured to set the applied gain to a sum of the applied gain and the applied gain multiplied by a rise rate parameter when the applied gain is not greater than the target gain, the rise rate parameter controlling a recovery time of the applied gain.
10. The hearing aid of claim 9 , wherein the processing circuit is configured to set the applied gain to 1 when the determined applied gain exceeds 1.
11. A method for signal processing in a hearing aid, comprising:
receiving an input signal from a microphone of the hearing aid;
filtering the input signal;
rectifying the filtered input signal;
generating an envelope of the rectified input signal;
accumulating a difference between an amplitude of the rectified input signal and an amplitude of the envelope;
determining an applied gain using the accumulated difference;
producing an output signal by applying the applied gain to the input signal; and
producing an output sound based on the output signal using a speaker of the hearing aid,
wherein the signal processing includes signal processing in frequency domain.
12. The method of claim 11 , wherein determining the applied gain comprises:
calculating a target gain using the accumulated difference; and
determining the applied gain based on the target gain.
13. The method of claim 12 , wherein calculating the target gain comprises setting the target gain to a minimum target gain value when the calculated target gain is less than the minimum target gain.
14. The method of claim 13 , wherein determining the applied gain comprises setting the applied gain to the target gain when the applied gain is greater than the target gain.
15. The method of claim 14 , wherein determining the applied gain further comprises setting the applied gain to a sum of the applied gain and the applied gain multiplied by a rise rate parameter when the applied gain is not greater than the target gain, the rise rate parameter controlling a recovery time of the applied gain.
16. The method of claim 15 , further comprising normalizing the accumulated difference using the rectified acoustic signal, and wherein calculating the target gain comprises calculating the target gain using the normalized accumulated difference.
17. The method of claim 16 , wherein calculating the target gain comprises dynamically calculating the target gain by subtracting the normalized accumulated difference from 1.
18. The method of claim 16 , wherein determining the applied gain further comprises setting the applied gain to 1 when the determined applied gain exceeds 1.
19. The method of claim 16 , further comprising decimating the input signal before rectifying the input signal.
20. The method of claim 16 , further comprising scaling the threshold signal by multiplying the envelope by a threshold shift, and wherein accumulating the difference between the amplitude of the rectified input signal and the amplitude of the envelope comprises accumulating the difference between the amplitude of the rectified input signal and the amplitude of the scaled envelope.