Feedback scan for hearing aid

1. A hearing aid, comprising:

a sensor that receives ambient sound from around a patient; and

a driver that stimulates the anatomy of the patient;

wherein the hearing aid has an operational mode in which the driver stimulates the anatomy of the patient in response to the sound received at the sensor;

wherein the hearing aid has a test mode in which a test frequency is stepped through a predetermined range of frequencies; and wherein at each test frequency, the driver is driven with a sinusoidal driver signal at the test frequency, the sensor detects a sinusoidal sensor signal at the test frequency, and a comparison of the sensor signal to the driver signal produces an amplitude and a phase for the test frequency,

wherein the sinusoidal driver signal and the sinusoidal sensor signal are sampled at intervals that are spaced apart by one-fourth of an oscillation period at the test frequency.

2. The hearing aid of claim 1 , wherein four samples of the sinusoidal driver signal and four samples of the sinusoidal sensor signal are saved at each test frequency as voltage levels.

3. The hearing aid of claim 2 , wherein the samples of the sinusoidal driver signal are offset in time from the samples of the sinusoidal sensor signal by a predetermined offset for each test frequency.

4. The hearing aid of claim 3 , wherein the predetermined offset is zero for all test frequencies.

5. The hearing aid of claim 4 , wherein for each test frequency:

the four samples of the sinusoidal driver signal are denoted as D 1 , D 2 , D 3 and D 4 ;

the four samples of the sinusoidal sensor signal are denoted as S 1 , S 2 , S 3 and S 4 ;

the system amplitude is given by:

[( S 3 −S 1) 2 +( S 4 −S 2) 2 ] 1/2 /[( D 3 −D 1) 2 +( D 4 −D 2) 2 ] 1/2 ;

and the system phase is given by:

a tan 2[( D 4 −D 2), ( D 3 −D 1)]−a tan 2[( S 4 −S 2), ( S 3 −S 1)].

6. The hearing aid of claim 3 , wherein the predetermined offset is a constant time for all test frequencies.

7. The hearing aid of claim 3 , wherein the predetermined offset is a constant phase for all test frequencies.

8. The hearing aid of claim 1 , wherein the hearing aid is surgically implantable in the patient, is a cochlear device, or is a middle ear device.

9. A device for restoring the hearing of a patient, comprising:

a sensor for converting ambient sound around the patient into a corresponding input electrical signal;

an audio processing unit which receives the input electrical signal and produces an output electric signal; and

a driver for converting the output electrical signal into a stimulation signal that can be received by an anatomy of the patient;

wherein the audio processing unit includes a test mode during which the audio processing unit drives the driver with a sinusoidal driver signal at a predetermined frequency, receives through the sensor a sinusoidal sensor signal at the predetermined frequency, and samples and stores at least four voltage levels each for the sensor and driver signals; and

wherein the voltage levels are sampled at intervals that are spaced apart by one-fourth of an oscillation period at the predetermined frequency.

10. The device of claim 9 , further comprising a module external to the patient for reading the stored at least four voltage levels each for the sensor and driver signals.

11. The device of claim 10 , wherein the stored at least four voltage levels determine a feedback gain and a feedback phase shift at the predetermined frequency.

12. The device of claim 9 , wherein the predetermined frequency is stepped in discrete increments over a predetermined frequency range.