Microphone apparatus

Abstract: A microphone apparatus using two microphones has a circuit for processing output signals of the two microphones so as to obtain non-directional characteristics in a low frequency region and uni-directional characteristics in a high frequency region. When this microphone apparatus is incorporated in an appliance containing acoustic noise source and vibration source therein, acoustic noise, vibration noise and wind noise are reduced to prevent reduction of the S/N ratio when picking up the sound, so that recording of excellent quality sound is realized.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microphone apparatus to be built into an appliance possessing an acoustic noise source or a vibration source therein. 2. Description of the Prior Art In collection of sound using a microphone, the quality of sound signal deteriorates due to acoustic noise other than the desired sound, vibration noise caused by mechanical vibration and wind noise caused by wind. In particular in such an appliance as video camera, not only the mechanical system contained inside generates acoustic noise and vibration, but also the appliance itself is often used outdoors. when incorporating a directional microphone or a non-directional microphone in such appliance, the S/N ratio in sound collection drops owing to the following factors. Since the microphone is close to the vibration source or acoustic noise source, the absolute level of the acoustic noise or vibration applied to the microphone increases. Since the microphone is close to the acoustic noise source, a proximity effect occurs in a directional microphone, and the pressure sensitivity is raised in the front and rear directions in low frequency region so as to be susceptible to the acoustic noise generated by the mechanical system. The directional microphone is more liable to be influenced by the vibration than the non-directional microphone. The directional microphone is more liable to be influenced by the wind than the non-directional microphone. The non-directional microphone cannot eliminate acoustic noise by directivity. A microphone apparatus having a function for reducing the wind noise have been already proposed (for example, the Japanese patent publication Nos. H01-39194, H01-39195). The microphone apparatus comprises a non-directional microphone, a uni-directional microphone, a low pass filter for removing the high frequency components of output signal of the non-directional microphone, a high pass filter for removing the low frequency components of output signal of the uni-directional microphone, an adder for synthesizing the outputs of the two filters, and means for detecting the intensity of wind noise. In thus composed microphone apparatus, by detecting the intensity of the wind noise, the wind noise is reduced by deriving the output signal of the uni-directional microphone when the wind is weak, and the combined signal of the high frequency components of the output signal of the uni-directional microphone and the low frequency components of the output signal of the non-directional microphone when the wind is strong. In such conventional microphone apparatus, however, although the wind noise can be reduced, if the apparatus is built into an appliance having a noise or vibration source, it is impossible to reduce the acoustic noise increasing due to the proximity effect and mechanical vibration when the wind is weak. The present invention provides a microphone apparatus comprising: a first non-directional microphone; a second non-directional microphone disposed at a distance from the first non-directional microphone so that main axes of the first and second non-directional microphones are aligned on a straight line; a delay unit for delaying an output signal of the second non-directional microphone; a high-pass filter for removing low frequency components of an output signal of the first non-directional microphone; and a subtractor for subtracting an output signal of the delay unit from an output signal of the high-pass filter. An advantage of the invention is that a microphone apparatus is provided which is capable of reducing the wind noise and the acoustic and vibration noises generated by a mechanical system of an appliance in which the microphone apparatus is incorporated, and which lowers reduction of S/N ratio in sound collection. Fig. 1 is a block diagram showing a microphone apparatus according to an embodiment of the invention; Fig 2 is a diagram showing a frequency response of the microphone apparatus of Fig. 1. Fig. 1 is a block diagram of a microphone apparatus according to an embodiment of the invention. In Fig. 1, the X-direction is referred to as the front direction, the -X direction as the rear direction, and the Y-direction as the side direction. More specifically in Fig. 1, numeral 1 is a non-directional microphone, 2 is a non-directional microphone disposed at a distance in the rear direction to the non-directional microphone 1 with the main axis aligned on a straight line with that of the non-directional microphone 1, 3 is a delay unit for delaying an output signal of the non-directional microphone 2, 4 is a high-pass filter for removing low frequency components of an output signal of the non-directional microphone 1, and 5 is a subtracter for subtracting an output signal of the delay unit 3 from an output signal of the high-pass filter 4. In thus composed microphone apparatus, the operation is as follows. The two non-directional microphones are disposed at a spacing therebetween, and the output signal of one non-directional microphone is delayed by a delay time corresponding to the distance between the two microphones. The delayed signal is subtracted for the output of the other non-directional microphone, so that the same directional characteristic as that of a uni-directional microphone can be obtained. Accordingly, the output signal of the non-directional microphone 2 is delayed by the delay unit 3. The delayed signal from the delay unit 3 is combined with the output signal of the non-directional microphone 1 which has been eliminated of the low frequency components by the high-pass filter 4,-so that only the high frequency components are made uni-directional. Fig. 2 shows a frequency response of the microphone apparatus of Fig. 1. According to the characteristic as shown in Fig. 2, the microphone apparatus of Fig. 1 can reduce the acoustic noise in the high frequency region and vibration noise in the low frequency region generated by the mechanical system contained in an appliance in which the microphone apparatus is incorporated, and the wind noise, thereby preventing reduction of the S/N ratio when collecting sound.

Claims: A microphone apparatus comprising: a first non-directional microphone (1); a second non-directional microphone (2) disposed at a distance from the first non-directional microphone so that main axes of the first and second non-directional microphones are aligned on a straight line; a delay unit (3) for delaying an output signal of the second non-directional microphone; a high-pass filter (4) for removing low frequency components of an output signal of the first non-directional microphone; and a subtractor (5) for subtracting an output signal of the delay unit from an output signal of the high-pass filter.

Inventors: KOBAYASHI HIROSHI, MATSUMOTO MICHIO, NAONO HIROYUKI, ONO KIMINORI, YAMASHINA YUUJI, KOBAYASHI, HIROSHI, MATSUMOTO, MICHIO, NAONO, HIROYUKI, ONO, KIMINORI, YAMASHINA, YUUJI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1990
Main classification: H04R3
IPC codes: H04R3