Victor Company of Japan, Limited

Kaoru Totsuka

Yukinobu Ishigaki

Naotaka Miyaji

Makoto Yamamoto

Yutaka Haramoto

Takao Kawasaki

A noise reducing apparatus consists of a compression system and an expansion system. The compression system comprises a pre-emphasis circuit for performing a pre-emphasis operation with respect to an input signal, a first variable gain control circuit for giving a level compression characteristic to an output signal of the pre-emphasis circuit, to produce an output signal to a transmission path, a first control voltage producing circuit for dividing the output signal of the first variable gain control circuit into a plurality of bands, to produce a plurality of control voltages respectively given mutually different bands, a first weighting circuit for respectively and relatively weighting the plurality of control voltages obtained from the first control voltage producing circuit, and a first adding circuit for adding the plurality of control voltages obtained from the first weighting circuit, to obtain a first control voltage and apply this first control voltage to the first variable gain control circuit. The expansion system similar to the compression system, comprises a second variable gain control circuit for giving a level expansion characteristic to the level compressed signal obtained through the above transmission path, where the level expansion characteristic is complementary to the level compression characteristic.

Noise reducing apparatus

A variable directivity microphone device comprises a microphone unit assembly provided and arranged with at least three microphone units, wherein the three microphone units are mutually separated by predetermined distances, and front faces of a first and second microphone units of the three microphone units are provided and arranged facing the front surface of the microphone unit assembly while the front face of a third microphone unit is provided and arranged in a direction opposite to those of the first and second microphone units, a first and second variable resistors respectively having a terminal at one end, an intermediate terminal, and a terminal at the other end, wherein respective sliders are mutually linked or ganged and movable between a first, second, and third positions corresponding to the terminals, where the first variable resistor has the terminals at both ends thereof respectively connected to the output sides of the second and third microphone units and the intermediate terminal thereof connected to ground, an adder for adding and mixing the output of the first microphone unit and a signal obtained from the slider of the first variable resistor, and a frequency characteristic compensating circuit having an operational amplifier, for compensating for the frequency characteristic of the output signal of said adder. The second variable resistor has the terminals at both ends thereof respectively connected between the output side and input side of the operational amplifier, and the slider thereof connected to the output side of the operational amplifier. The frequency characteristic compensating circuit further comprises a frequency characteristic circuit connected in parallel with the second variable resistor, and the microphone device varied of its directivity from non-directivity, to primary unidirectivity, and then to secondary unidirectivity, as the sliders of the first and second variable resistors vary from the above first, to second, and then to third positions.

Variable-directivity microphone device

Three microphone units of first order sound pressure gradient unidirectional type are disposed in a casing having front and rear portions at both sides in such a manner that the center axes of the microphone units are aligned on the same axis. Two among the three microphone units are arranged to face the front portion of the casing, and remaining one microphone unit is arranged to face the rear portion of the casing. The output signals of the three microphone units are combined at a variable ratio so that the directivity of the microphone system can widely vary from nondirectivity via first order sound pressure gradient unidirectivity to second order sound pressure gradient unidirectivity. The output signals of two microphone units used for obtaining second order sound pressure gradient unidirectivity may be respectively applied to high pass filters before being combined, and the combined signal is fed to an equalizer. If an equalizer having modified frequency characteristic is employed, such high pass filters may be omitted.

Variable directional microphone system

In a noise reduction system including a compressor and an expander having a complementary frequency response characteristic to the frequency response characteristic of the compressor, the compressor includes a high frequency emphasis variable frequency filter and a low frequency emphasis variable gain filter which are connected in a series circuit between input and output terminals and which respectively vary their parameters in response to the respective high and low frequency components of the compressor output. The expander includes a high frequency de-emphasis variable frequency filter and a low frequency de-emphasis variable gain filter which are connected in a series circuit between input and output terminals and which respectively vary their parameters in response to the respective high and low frequency components of the expander input.

Noise reduction system having series connected low and high frequency

A variable-directivity microphone device comprises a microphone unit having a plurality of microphones, a circuit which resultingly adds the low-frequency range components of the output signal of one of the microphones of the microphone unit and mixes with the output signal of the other microphone so that only the high-frequency range components cancel each other, and an equalizer which corrects the characteristic of the mixed signal. The above effective mixing is performed under varying mixing states.

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Yokohama, Japan

Kaoru Totsuka