Microphone matching

The two microphones in a directional dual microphone system have to react in exactly the same manner to a given sound. If they do not, directionality will not be optimal and the user will not receive the full benefit.
 

Continuous microphone matching is necessary

Buying microphones as matched sets does not in itself guarantee that the microphones function in an identical fashion.

The matching done by the microphone manufacturer may not be as accurate as one would hope for. Also, the two microphones’ characteristics may change independently over time.

Consequently, Widex uses an adaptive microphone matching system that continuously makes sure the two microphones function completely identically.

The Multipoint microphone matching system is found at the very beginning of the hearing aid signal processing, so that the two microphone signals are matched before moving to the next step in the hearing aid sound processing sequence.
 

The multipoint microphone matching system

The multipoint microphone matching system takes advantage of the fact that all our microphones have the same general frequency response: the low frequencies are dampened and the higher frequencies are let through with the same sensitivity for a wide frequency area.

The frequency where the dampening sets in is called the roll-off frequency.


Illustration : The frequency responses of two unmatched microphones

Microphone matching is achieved by measuring the difference between the two microphones’ sensitivity at six distinct frequencies around a common kneepoint in the microphone characteristics.


Illustration: A close-up of the distribution of matching points along the frequency responses in the frequency region marked by red dotted lines in the figure above

The system then alters the phase delay and sensitivity of one of the microphones until they are identical to the other microphone’s.


Illustration: The frequency responses of two matched microphones.