1. Technical Field
The present disclosure relates to an array microphone apparatus and in particular to an array microphone apparatus for generating a beam forming signal and a beam forming method thereof.
2. Description of the Related Art
For ease of understanding, the following is a glossary of certain terms used herein:                First order difference pattern: a pattern that is formed as the difference in pressure between two points in space. The two-port microphones often used in hearing aids are of this type.        Cardioid: a first order difference pattern that has maximum response in the forward direction and a single null to the rear.        Bidirectional: general name for any pattern that has equal maximum response in both the front and rear directions.        
Many communication system and voice recognition devices are designed for use in noisy environments. Examples of such applications include communication and/or voice recognition in cars or mobile environments (e.g., on street), conference calls, Flat panel TV's, Laptop or other computers, camera modules, Smartphones, and the like.
For these applications, the microphones in the system may pick up both the desired voice and also noise. The noise can degrade the quality of voice communication and speech recognition performance if it is not dealt with in an effective manner able to improve communication quality and voice recognition performance.
Noise suppression may be achieved using various techniques. One of these techniques, known in the state of the art, is the so called array microphone technique.
With reference to this technique, it is to be noted, as known to a skilled man, that a substantial directivity can only be obtained with a spatial distribution larger than the minimum relevant wavelength.
In the array microphone technique it is possible to distinguish two meaningful groups of linear arrays characterized by the position of the microphones and the main source angles:                End Fire beam forming, and        Broad Side beam forming.        
It is defined broadside beam forming in the array depicted in FIG. 1 where the microphones M1, . . . , Mn are placed along the x-axis, and the main beam is perpendicular (y-axis) to the line of microphones. Particularly the sound coming from a 90° direction is kept, and the sound coming from the 0° direction is deleted.
It is defined end fire beam forming in the array depicted in FIG. 2 where the microphones M1, . . . , Mn are placed along the y-axis and the main beam is in the direction of the microphones, i.e., the x-axis. Particularly the sound coming from a 0° direction is kept, and the sound coming from the 90° direction is deleted.
It is to be noted also that, the end fire technique is simpler with respect to the broad side beam forming. However the end fire technique has few applications since deleting front signal sources is generally not suitable for Laptop or Flat panel TV modules.
On the other side the broad side beam forming technique is the solution most implemented since it provides noise suppression, wind noise suppression (mobile phones makers), and speech enhancement sound equalization.
However, the broad side beam forming technique is generally realized with a complex algorithm performing Fast Fourier Transform (FFT), adaptive suppression, and also inverse FFT.
Therefore, the broad side beam forming technique often uses a powerful digital signal processor (DSP) or microcontroller, software development memory, and several million instructions per second (MIPS) allocation for the algorithm.
Further it is to be noted that the simplest broad side beam forming technique works by taking advantages from the placement of the microphones or by using delays, but this technique works properly only for a fixed frequency.
These techniques appear to be very capable but are not always cost-effective and flexible to use in practical situations.
Thus effective suppression of noise in communication system and voice recognition devices is desirable using a cost effective apparatus.