JPH05241582A - Noise canceler - Google Patents

Abstract

PURPOSE:To eliminate a noise component mixed in a sound signal from a microphone. CONSTITUTION:A microphone 1 is arranged close to a speaker and a microphone 2 is arranged close to a noise sourse. Then, since a noise is inputted to the microphone 1 delayed from the microphone 2, the delay time of a delay circuit 32 is set to a value adding the propagation delay of the noise and the delay of the delay circuit 31. Further, since the level of the noise inputted to the microphone 2 is higher than the level of the noise inputted to the microphone 1, a signal level is attenuated by a variable gain adjusting circuit 42 and the levels of the noise components in the outputs of the variable gain adjusting circuits 41, 42 are made to coincide. Thus, the noise components are inputted to a subtractor 5 with the same phase and with the same level and the noise components are canceled and only a sound signal is outputted from the subtractor 5. An echo canceler 6 operates in adaptive when temperature and humidity are changed further and cancels and eliminates the noise component perfectly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise canceller for removing a noise component mixed in a voice signal.

[0002]

2. Description of the Related Art For example, in a remote conference, conference rooms separated by a space are connected by a communication line and a conference is held using a microphone and a speaker. At a lecture or the like, a speaker's voice is expanded inside the room by a microphone. However, in such a teleconference or lecture, not only the voice of the speaker of the teleconference or the speaker of the lecture (hereinafter simply referred to as the speaker) but also noise generated in the room is picked up by the microphone. Therefore, noise components such as the sound of the air conditioner, the sound of the fan of computer equipment and office equipment, the sound of the printer and the sound of the listener are mixed in the sound signal from the microphone, and as a result, the sound is emitted from the speaker. The voice that is heard is buried in noise, making it difficult to hear.

Therefore, conventionally, a microphone having a strong unidirectional directivity is used so that only the voice of the speaker is input to the microphone to prevent noise from entering.

[0004]

However, when a strongly directional microphone is used, it is good when the speaker speaks at a fixed position, but when the speaker changes position, the voice signal is greatly attenuated. Resulting in. Further, in the case of a remote conference, since there are many speakers, a large number of microphones must be installed when a strongly directional microphone is used.

One method of preventing noise contamination is to eliminate noise generation from air conditioning equipment and office equipment, but this requires a huge equipment cost and is practically impossible.

An object of the present invention is to provide a noise canceller which solves such a problem and removes a noise component mixed in a voice signal from a microphone.

[0007]

SUMMARY OF THE INVENTION A noise canceller according to the present invention has a first delay for delaying a signal from a first microphone.
A variable delay circuit, and a first variable gain adjusting circuit for adjusting the level of the signal from the first microphone,
A second variable delay circuit that delays the signal from the second microphone, a second variable gain adjustment circuit that adjusts the level of the output signal of the delay circuit, the first variable delay circuit, and the first variable delay circuit. And a subtractor for subtracting the output signal of the second variable gain adjustment circuit from the signal from the first microphone delayed and level-adjusted by the variable gain adjustment circuit No. 1, and using the output signal of the subtractor as a transmission input signal. And an echo canceller using the output signal of the second variable delay circuit as a received input signal.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows an example of the noise canceller according to the present invention. This noise canceller includes a variable delay circuit (D) 31 for delaying a signal from a microphone 1 for picking up a voice of a speaker, a variable gain adjusting circuit 41 which receives an output signal of the delay circuit 31, and noise. A variable delay circuit (D) 32 that delays a signal from a microphone for pickup, a variable gain adjustment circuit 42 that receives the output signal of the delay circuit 32 as an input, and a variable gain adjustment based on the output signal of the variable gain adjustment circuit 41. A subtractor 5 that subtracts the output signal of the circuit 42, an echo canceller 6 that outputs the output signal of the subtractor 5 as a transmission input signal, an output signal of the variable delay circuit 32 as a reception input signal, and an output signal to the terminal 7. Is equipped with. And the microphone 1
As shown in FIG. 2, the microphone 9 is arranged close to the speaker 9, while the microphone 2 is arranged close to the noise source 10. Reference numeral 8 is the noise canceller of this embodiment.

In such a structure, the microphone 1
Is separated from the noise source 10, noise is input to the microphone 1 later than the microphone 2. Therefore,
The delay time of the delay circuit 32 is set to a value obtained by adding the propagation delay of the sound wave and the delay of the delay circuit 31. Further, since the noise level input to the microphone 2 is higher than the noise level input to the microphone 1, the signal level is attenuated by the variable gain adjusting circuit 42, and the noise component of the output of the variable gain adjusting circuits 41, 42 is reduced. Match the levels. By setting the variable delay circuit and the variable gain adjusting circuit as described above, the noise component is input to the subtractor 5 at the same phase and at the same level, and as a result, the noise component is canceled and only the audio signal is output. Is output from the subtractor 5.

By the way, sound waves propagating in the air are easily affected by the environment such as temperature and humidity, and the delay time and the level fluctuate due to the change of the environment. The echo canceller 6 is provided in order to cope with such a variation, and when the noise component is not completely canceled due to the phase or level shift due to the change in the environment, but appears in the output of the subtractor 5. The echo canceller 6 operates adaptively to completely cancel and remove noise components. Therefore, the noise component is surely removed not only in the environment assumed in advance but also when the environment changes.

The echo canceller 6 can reduce the hardware scale of the adaptive filter of the echo canceller 6 by reducing its control time by the delay time of the delay circuit 32.

[0012]

As described above, the noise canceller of the present invention includes the first variable delay circuit for delaying the signal from the first microphone and the first variable delay circuit for adjusting the level of the signal from the first microphone. Variable gain adjustment circuit of
A second variable delay circuit that delays the signal from the second microphone, a second variable gain adjustment circuit that adjusts the level of the output signal of the delay circuit, a first variable delay circuit, and a first variable delay circuit. A second signal from the signal from the first microphone delayed and level-adjusted by the variable gain adjustment circuit
Of the variable gain adjustment circuit, and an echo canceller that uses the output signal of the subtractor as a transmission input signal and the output signal of the second variable delay circuit as a reception input signal. And

Therefore, in the noise canceller of the present invention,
By properly delaying the signal with the delay circuit and appropriately adjusting the signal level with the variable gain adjustment circuit, the phase and level of the noise component are matched and canceled at the input of the subtractor, and the noise mixed in the voice signal The components can be removed. Further, even when the environment for sound waves changes and the noise component cannot be completely removed at the output of the subtractor, the noise component can be adaptively removed by the action of the echo canceller.

Therefore, by using the noise canceller of the present invention, it is possible to remove the noise component and obtain only the voice signal even when the microphone is used to collect the sound in a bad environment where the noise is large, and the listener can easily hear it. It becomes possible to provide voice. Further, a general omnidirectional microphone may be used as the speaker microphone, which is advantageous in terms of cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a noise canceller of the present invention.

FIG. 2 is a diagram showing an arrangement of microphones connected to the noise canceller of FIG.

[Explanation of symbols]

 1, 2 Microphone 5 Subtractor 6 Echo canceller 7 Terminal 8 Noise canceller 9 Speaker 10 Noise source 31,32 Variable delay circuit 41,42 Variable gain adjustment circuit

Claims (1)

[Claims] 1. A first variable delay circuit for delaying a signal from a first microphone, a first variable gain adjustment circuit for adjusting a level of a signal from the first microphone, and a second variable delay circuit. A second variable delay circuit for delaying the signal from the microphone and a second variable delay circuit for adjusting the level of the output signal of the delay circuit.
Variable gain adjusting circuit, and the output signal of the second variable gain adjusting circuit from the signal from the first variable delay circuit and the first microphone delayed and adjusted in level by the first variable gain adjusting circuit. And a echo canceller having an output signal of the subtractor as a transmission input signal and an output signal of the second variable delay circuit as a reception input signal.