Patent Application
20140363001
1. Field of the Invention
The present invention relates to array microphone calibration technology, and in particular, relates to small array microphone calibration technology.
2. Description of the Related Art
A microphone, which is a transducer that converts sound into an electrical signal, can be used for various applications such as voice communication or voice recognition.
An array microphone can have any number of microphones. The array microphone captures more sound information and can achieve better performance than a single microphone. However, mismatching among the microphones in the array microphone occur, such as the phase mismatch, sensitivity mismatch and the frequency response mismatch.
Small array microphones (SAM) are a new type of array microphones, which require there be only 5 mm between any two microphones. Therefore, the small array microphone can be used in any environment with greater application. Compared with the traditional wide array microphones (any two microphones therein has to be apart from each other by at least 30 mm), the parameter mismatch problems in the small array microphones are more serious and therefore require a completely different algorithm to process sounds and voices.
The present invention provides a method for calibrating performance of a small array microphone (SAM), wherein the small array microphone comprises at least two microphones. The method comprises: measuring parameters of the microphones; recording the parameters in a storage media; and calibrating acoustic performance of the array microphone according to the parameters recorded in the storage media.
A detailed description is given in the following embodiments with reference to the accompanying drawings.
The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
The way for arranging the array microphone in the sound insulation cabin should not be limited to the embodiments in
In the recording procedure (step S104), the parameters such as the phase, the sensitivity and the frequency response of the microphones measured in the measuring procedure described above are then recorded in a storage media. In an embodiment, the storage media of the present invention is a non-volatile memory such as an EEPROM, flash memory, or hard disk. The storage media may be multiple time access-able devices such as flash memories, EEPROM memories or multiple programmable memories, or one-time programmable devices such as one-time programmable (OTP) memories, Efuse cells and Laser trim structures. The storage media of the present invention can be integrated with the array microphone, or configured in a device such as a computer that is separate from but connected to the array microphone.
In the calibration procedure (step S106), the acoustic performance of the array microphone can be calibrated according to the parameters of the microphones (e.g., the phase, the sensitivity and the frequency response) which are recorded in the recording procedure. The present invention provides embodiments for calibrating the phase mismatch (delay) as described below:
x1(t)=h1(t)*s(t); and
x2(t)=h2(t)*s(t),
where the symbol “*” denotes the convolution operation, the symbols h1(t) and h2(t) respectively denote the impulse responses from the source to the two microphones 402 and 404. The received test signals x1(t) and x2(t) can be combined into the following equation:
x1(t−t0)=x2(t) (equation 1),
where t1 is a delay which compensate for the difference between the propagation paths from the source to the two microphones. Then the following equation for the two filters w1(t) and w2(t) may be designed to eliminate the delay:
w1(t)*x1(t−t0)=w2(t)*x2(t) (equation 2).
To simplify the calculation, equation 2 may be translated to the Z domain as follows:
W1(z) W2(z)=z−D (equation 3),
where the symbol “D” represents the delay in the Z domain, having a nonnegative value. In some embodiments, the following equation may apply to the filters:
minimize E [w1(t)*x1(t−t0)−w2(t)*x2(t)]2 (equation 4).
Note that the calibration procedure described above can be implemented for an array microphone that has two or more than two microphones, which receives sounds from several sources with different incident angles. The calibration procedure can also be performed in the time domain, the frequency domain, or others.
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
