The devices such as a microphone array including a plurality of sound receiving units using a microphone such as a condenser microphone outputting sound signal based on received sound and performing various acoustical signal processes based on the sound output by the sound receiving unit has been developed. Such device including a plurality of sound receiving units is capable of suppressing noise by performing processing such as “delay-and-sum” processing emphasizing a target sound by synchronizing each of the sound signals for each of the sound receiving units and adding the sound signals, and synchronized subtraction forming a dead zone for the noise source by synchronizing each of the sound signals and subtracting one from the other.
The noise suppressing device includes a main sound receiving unit and a sub sound receiving unit for generating a sound signal based on received sound, a delay unit for delaying the sound signals, a correcting unit for correcting the sound signals, and a subtracting unit for subtracting the sound signals. The main sound receiving unit and sub sound receiving unit are arranged along the arrival direction of sound from a speaker with adequate spacing, and the speaker produces sound from the side of the main sound receiving unit. The analog sound signals generated by the main sound receiving unit and the sub sound receiving unit are amplified, converted to digital signals, and furthermore converted to components on the frequency axis.
The delay unit delays the sound signal for the sub sound receiving unit by a delay time τ, and outputs the delayed sound signal to the correcting unit. The delay time τ is based on the time required for arriving of the sound from the side of the sub sound receiving unit at the main sound receiving unit after the sound reached to the sub sound receiving unit. The level of the sound signal output from the sub sound receiving unit is matched to the level of the sound signal output from the main sound receiving unit including the correcting unit for correcting the delayed sound signal output from the sub sound receiving unit. The subtracting unit subtracts the corrected sound signal output for the sub sound receiving unit from the sound signal output for the main sound receiving unit. In this way, the noise suppressing device suppresses noise by performing synchronized subtraction of the sound signals and forming a directional dead zone on the side of the sub sound receiving unit.
When a disturbance such as wind blows against a noise suppressing device including a plurality of sound receiving units, wind noise is generated having characteristics in increasing of the level difference between the sound signals output by each of the sound receiving units, decreasing of the correlation between the sound signals, concentration of power on the low frequency region, disturbing of the phase difference spectrum between sound signals becomes disturbed and so on.
For example, due to the wind noise, the calculation of the correction value performed by a correction value calculating unit is disturbed so that the levels of the sound signals output from sub sound receiving unit become mismatched. Then abnormal conditions occurs, such as distortion of sound due to overcorrecting the level of the sound signal, or remaining noise due to under correcting the level of the sound signal. In addition, when wind blows against the sub sound receiving unit, the sound signal output by the sub sound receiving unit is subtracted from the sound signal output by main sound receiving unit. Then abnormal condition may occur such as generating of the component of the wind noise in the sound signal output from the sub sound receiving unit.
Techniques for suppressing wind noise are disclosed in Japanese Patent No. 3,086,539, Japanese Patent No. 3,283,423 and Japanese Laid-open Patent Publication No. 116-311583. Moreover, a technique of determining the strength of the wind using two microphones is disclosed in Japanese Laid-open Patent Publication H5-308696.