The present invention relates to a microphone, particularly to a miniature electronic directional microphone.
In a variety of occasions where sounds need picking up, such as a reporter's interview, a competition broadcast, an outdoor filming, there is noise coming from all directions. A common microphone would pick up many unnecessary noises in addition to the sounds intended to pick up. Therefore, a directional shotgun microphone is usually used in the above-mentioned occasions to pick up sounds coming from a specified direction and avoid noise interference from other directions.
A US publication No. 20110305359 disclosed a shotgun microphone, which comprises an acoustic tube, a connection member and a microphone unit, wherein the connection member connects the acoustic tube with the microphone unit. The conventional shotgun microphone uses the acoustic tube to achieve the pick-up directionality. The acoustic tube may be made of a porous material, whereby the acoustic tube can contract and extend to adjust the distance between the front end of the acoustic tube and the microphone unit, whereby is regulated the sound pick-up effect of the microphone unit.
The conventional shotgun microphone needs the acoustic tube to achieve the pick-up directionality. However, the acoustic tube is much larger than the microphone unit. Thus, the conventional shotgun microphone is bulky, hard to carry about, and inconvenient to use in many occasions.
The primary objective of the present invention is to solve the problem that the conventional shotgun microphone is bulky, hard to carry about and inconvenient to use.
To achieve the above-mentioned objective, the present invention proposes a miniature electronic shotgun microphone, which is used to pick up a sound source from a specified direction, and which comprises a pick-up member, an A/D (Analog/Digital) conversion unit, and a digital signal processor. The pick-up member includes a first pick-up unit, a second pick-up unit separated from the first pick-up unit by a first distance D1, and a third pick-up unit separated from the second pick-up unit by a second distance D2. The first, second, and third pick-up units respectively receive the sound source and output an analog signal. The A/D conversion unit electrically connects with the pick-up member, receives the analog signals, and converts the analog signals into a first digital signal, a second digital signal, and a third digital signal. The digital signal processor electrically connects with the A/D conversion unit and converts the first, second and third digital signals into a directional digital acoustic signal.
The first distance is greater than the second distance. Thus, the pick-up member has a maximum pick-up frequency greater than the frequency expressed by an Equation of
and
wherein c is the sound speed.
Via the design of the first, second and third pick-up units and the first and second distances D1 and D2, the miniature electronic shotgun microphone has a mini size and high directionality. Further, the pick-up member has the maximum pick-up frequency, whereby is increased the upper limit of the pick-up frequency and decreased the grating lobes and spatial aliasing.
The technical contents of the present invention are described in detail in cooperation with drawings below.
Refer to
The low-pass filter 40 electrically connects with the pick-up member 10, receives the analog signals output by the first pick-up unit 11, second pick-up unit 12 and third pick-up unit 13, filters out the high-frequency noise from the analog signals, and outputs the low-frequency portion of the analog signals. In one embodiment, the frequency allowed to pass the low-pass filter 40 depends on an effective bandwidth which is determined by the distance between the pick-up units (i.e. microphones). For example, the effective bandwidth may be decided by c/(2×D1) or c/(2×D2), wherein c is the sound speed, D1 is the first distance, and D2 is the second distance. Via the effective bandwidth is limited the bandwidth of the input sound source.
The A/D conversion unit 20 may either electrically connect with the pick-up member 10 through the low-pass filter 40 or directly electrically connect with the pick-up member 10. The A/D conversion unit 20 receives the analog signals and converts the analog signals into a first digital signal, a second digital signal, and a third digital signal. Refer to
the second digital signal may be expressed by Equation (2):
the third digital signal may be expressed by Equation (3):
In the above-mentioned equations, s(t) is the baseband signal, ωc is the center frequency, k is the wave vector=ωcκ/c, κ=(sin θ,cos θ), and c is the sound speed.
The digital signal processor 30 electrically connects with the A/D conversion unit 20 and receives the first, second and third digital signals, which are expressed by Equations (4) and (5):
wherein n1(t)−n3(t) are respectively the uncorrected noise signals of the pick-up units, a(κ) is the directional vector, and n(t) is the noise signal.
The digital signal processor 30 includes convex optimization software 31. The convex optimization software 31 is used to perform convex optimization process for Equation (5) to sets weights to the first, second and third digital signals to form a directional digital acoustic signal expressed by Equation (6):
h(ω,κ)=wHa(κ) (6)
wherein wH is the set weight.
Please refer to a paper “Convex Optimization” by S. Boyd and L. Vandenberghe (Cambridge University Press, New York, 2004). The method proposed in this paper is also included in the specification and regarded as a prior art used by the present invention.
In one embodiment, the digital signal processor 30 also includes golden-section search software 32. The digital signal processor 30 uses the golden-section search software 32 to set the values of the first and second distances D1 and D2 in a golden-section search way so as to optimize the directional digital acoustic signal. In one embodiment, the golden-section search is implemented with a calculation factor—Equation (7) and a target function—Equation (8):
wherein I is the section number of the set frequency range, ωi is the ith frequency point, and x a set variable that may be the first distance D1.
Please refer to a paper “Algorithms for Minimization without Derivatives” by R. P. Brent (Prentice-Hall, Englewood Cliffs, N.J., p. 48-75 (1973).-GSS-PI). The method proposed in this paper is also included in the specification and regarded as a prior art used by the present invention.
In one embodiment, the miniature electronic shotgun microphone of the present invention further comprises a D/A (Digital/Analog) conversion unit 50. The D/A conversion unit 50 electrically connects with the digital signal processor 30, receives the directional digital acoustic signal from the digital signal processor 30, and converts the directional digital acoustic signal into a directional analog acoustic signal for outputting.
Refer to
Suppose that the conventional equidistant array microphone has three microphones, and respectively define the spacing between the first and second microphones and the spacing between the second and third microphones to be d1 and d2. Thus, the maximum pick-up frequency f can be worked out according to Equation (9):
wherein c is the sound speed and d is the spacing between microphones.
In the example of
Therefore, it is observed in
Via the design of the first, second and third pick-up units and the design that the first distance is greater than the second distance, the miniature electronic shotgun microphone of the present invention has greater directionality pick-up effect. Further, the miniature electronic shotgun microphone of the present invention has a maximum pick-up frequency to increase the upper limit of the pick-up frequency and decrease grating lobes and spatial aliasing when the total pick-up length and the number of the pick-up units are identical to those of the conventional equidistant array microphone. The present invention can be fabricated with a microelectromechanical technology, whereby the present invention not only has higher directionality but also has miniature size, in comparison with the conventional shotgun microphone having an acoustic tube, and whereby the present invention is easy to carry about and applicable to various mobile electronics.
The embodiments described above are only to exemplify the present invention but not to limit the scope of the present invention. Any equivalent modification or variation according to the spirit of the present invention is to be also included within the scope of the present invention.
Number | Date | Country | Kind |
---|---|---|---|
101120192 A | Jun 2012 | TW | national |
Number | Name | Date | Kind |
---|---|---|---|
5793875 | Lehr et al. | Aug 1998 | A |
6681023 | Turnbull et al. | Jan 2004 | B1 |
8384685 | Kuo et al. | Feb 2013 | B2 |
20030072461 | Moorer | Apr 2003 | A1 |
20070253574 | Soulodre | Nov 2007 | A1 |
20110305359 | Ikeda et al. | Dec 2011 | A1 |
Number | Date | Country | |
---|---|---|---|
20130329907 A1 | Dec 2013 | US |