JPH04322598A - Microphone device - Google Patents

Abstract

PURPOSE:To realize a main body built-in microphone in which the effect of noise and vibration and wind noise caused from a mechanism system in a camcorder main body are reduced and sound with high S/N is recorded. CONSTITUTION:A low frequency component of an output signal of an omnidirectional microphone unit 11 is eliminated by a high pass filter 13 and a phase of an output signal of an omnidirectional microphone unit 12 is delayed by a phase shifter 14. An output signal of the phase shifter is added to an output signal of a high pass filter 13 with phase inversion and an equalizer 16 corrects the frequency characteristic and the result is outputted.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microphone device built into a device having a noise source or a vibration source therein, and more particularly to a microphone device built into a video camera.

0002

2. Description of the Related Art The main factors that degrade the quality of sound collected using a microphone include noise other than the intended sound, vibration noise due to mechanical vibrations applied to the microphone, and wind noise. Particularly in the case of devices such as video cameras, not only do mechanical systems such as internal tape drives generate noise and vibration, but the devices are often used outdoors.

[0003] Conventionally, such devices have built the microphone into the main body to reduce the distance between the microphone and these mechanical systems. and the absolute level of vibration increases.

0004

Generally, when the positional relationship between the microphone and the noise source is fixed, the influence of the noise can be removed by using a suitable directional microphone. However, in the case of directional microphones, the proximity effect occurs due to the proximity of the noise source to the microphone.
Since the sound pressure sensitivity in the front and back directions increases in the low frequency range, it becomes more susceptible to the effects of noise emitted by equipment, and the S/N
decreases. Additionally, directional microphones are more susceptible to vibration and wind than omnidirectional microphones.

[0005] Due to these factors, when a directional microphone is used as a built-in microphone, the S/N ratio during sound collection decreases and the sound collection quality deteriorates significantly.

In view of the above-mentioned problems, the present invention provides a built-in microphone that can reduce the effects of noise and vibration generated by the mechanical system within the video camera body, as well as wind noise, and can collect sound with a high S/N ratio. The purpose is to provide.

[0007]

[Means for Solving the Problems] In order to solve the above problems, the present invention uses two omnidirectional microphones to pick up sound omnidirectionally in the low frequency range and directionally in the high frequency range. This is what we do.

[0008]

[Operation] The microphone of the present invention is omnidirectional in the low frequency range, and has directivity with low sensitivity in the direction of the noise source in the high frequency range. Therefore, wind noise and low-frequency vibration noise, whose frequency components are concentrated in the low range, can be suppressed to the same level as omnidirectional microphones, and at the same time, the high-frequency directivity of the microphone depends on the distance between the noise source and the microphone. Because it is unaffected, the effects of noise can be removed in high frequencies.

[0009]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(FIG. 1) shows the configuration of a microphone device according to a first embodiment of the present invention, in which 11 and 12 are omnidirectional microphone units;
3 is a high-pass filter, 14 is a phase shifter, 15 is a subtracter,
16 is an equalizer for correcting frequency characteristics. A high-pass filter 13 removes low frequency components of the output signal of the unit 11, and a phase shifter 14 delays the phase of the output signal of the unit 12. high pass high pass 1
The output signal from the phase shifter 14 is added to the output signal from the phase shifter 14 in reverse phase, and the frequency characteristics are corrected by the equalizer 16 and output.

First, the operation of the microphone device of this embodiment in a high frequency range above the cutoff frequency of the high-pass filter 13 will be described. In the microphone device of this embodiment, a phase shifter 14 applies a phase delay to the output of the omnidirectional microphone unit 12 according to the interval between the two units 11 and 12, and this signal is passed through a high-pass filter 13.
By adding the reverse phase to the output of the omnidirectional microphone unit 11 that has passed through, the microphone becomes a primary sound pressure gradient type microphone in this frequency band. The directivity D at this time is a function of the angle θ between the main axis of the microphone device and the direction in which the sound waves arrive.

0012

[Math 1]

It is given by: In (Equation 1), α is a constant determined by the time constant τ of the phase shifter 14, and α and τ
The relationship is that the distance between microphone units is d, and the speed of sound is c.
As,

[0014]

[Math 2]

It can be expressed as follows. Directivity is bidirectional when α=0, unidirectional when α=1, and omnidirectional when α=∞. Therefore, the time constant of the phase shifter 14 is set so as to obtain a directivity pattern in which the sensitivity decreases in the direction of the noise source. That is, by adjusting this time constant, the directivity pattern in the high frequency range can be changed depending on the direction of the noise source.

On the other hand, in the low frequency range below the cutoff frequency of the high-pass filter 13, the output of the subtracter 15 is almost the output of the phase shifter 14, so the directivity of the microphone device of this embodiment is omnidirectional. It becomes sex.

(FIG. 2) shows an example of the directional frequency characteristic of the microphone device of this embodiment before passing through the equalizer 16. The vertical axis in the figure is a relative value based on the sound pressure sensitivity of the omnidirectional microphone unit. Further, (FIG. 3) shows an example of the high frequency directivity pattern of the microphone device of this embodiment. In (FIG. 3), N is a noise source. As described above, the directivity of the microphone device of this embodiment is omnidirectional in the low frequency range, and directivity with low sensitivity in the direction of the noise source in the high frequency range. Therefore, wind noise and low-frequency vibration noise, whose frequency components are concentrated in the low range, can be suppressed to the same level as omnidirectional microphones, and at the same time, the high-frequency directivity of the microphone depends on the distance between the noise source and the microphone. Because it is unaffected, the effects of noise can be removed in high frequencies.

(FIG. 4) shows the configuration of a microphone device according to a second embodiment of the present invention, in which 41 and 42 are omnidirectional microphone units;
3 is a high-pass filter, 44 is a phase shifter, 45 is a subtracter,
46 is an equalizer, and 47 is a fixture. The difference from the first embodiment is that the main axes of the two units 41 and 42 are aligned, and the two units are fixed so that they vibrate together when vibration is applied to the two units. It is that you are. With this configuration, vibrations are transmitted to both units with the same amplitude and phase, so the high-frequency vibration sensitivity of the microphone device of this example is such that the vibrations are transmitted to both units at an angle of 90 degrees to the main axis of the microphone device. It shows the same characteristics as the sound pressure sensitivity when . (Figure 5) Equalizer 4
6 shows an example of the vibration sensitivity frequency characteristic of the microphone device of the present embodiment before passing through 6. The vertical axis in the figure is a relative value based on the vibration sensitivity of the omnidirectional microphone unit. As described above, in the band equal to or higher than the cutoff frequency of the high-pass filter 43, the vibration sensitivity of the microphone device of this embodiment is lower than that of the omnidirectional microphone unit. Note that the vibration sensitivity decreases as the value of α in (Equation 2) decreases. For other operations, please refer to the first
This is similar to the embodiment.

[0019]

As described above, the present invention uses two omnidirectional microphone units to pick up sound with omnidirectionality in the low frequency range, and directivity with low sensitivity in the direction of the noise source in the high frequency range. By doing this, it is possible to suppress wind noise and low-frequency vibration noise to the same level as an omnidirectional microphone, and at the same time, it is possible to eliminate the effects of noise in the high-frequency range. Furthermore, by arranging the main axes of each microphone unit so that they are aligned and facing the same direction, and by fixing the two units so that they vibrate as a unit, high-frequency vibration sensitivity is achieved in a non-directional manner. vibration sensitivity is lower than that of the standard microphone unit. Therefore, by installing the microphone device of the present invention in a video integrated camera, it is possible to prevent the S/N from decreasing during sound collection.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of directional frequency characteristics of the microphone device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an example of high-frequency directivity characteristics of the microphone device according to the first embodiment of the present invention.

FIG. 4 is a block diagram showing the configuration of a second embodiment of the present invention.

FIG. 5 is a diagram showing an example of vibration sensitivity frequency characteristics of a microphone device according to a second embodiment of the present invention.

[Explanation of symbols]

11, 12, 41, 42 Omnidirectional microphone unit 13, 43 High pass filter 14, 44 Phase shifter 15, 45 Subtractor 16, 46 Equalizer 47 Fixture N Noise source

Claims (2)

[Claims] 1. First and second omnidirectional microphones arranged in a straight line with a spacing between them; and a high-pass filter that removes low frequency components of an output signal of the first omnidirectional microphone. A microphone comprising: a phase shifter that delays the phase of the output signal of the second omnidirectional microphone; and a subtracter that mixes the output of the phase shifter with the output of the high-pass filter in reverse phase. Device. Claim 2: Claim 1, wherein the two omnidirectional microphones are arranged so that their main axes are aligned and facing the same direction, and are fixed so that the two omnidirectional microphones vibrate together. Microphone device as described.