JPH0576094A - Sound collecting device - Google Patents

Abstract

PURPOSE:To provide the small scale sound collecting device capable of improving the collecting characteristic of the objective sound by reducing the recording level of the sound other than the objective sound to be recorded at the time of recording using a microphone. CONSTITUTION:The signal level passing two-system band-pass filter groups 15 and 16 is detected, the level change point is detected by a signal processor 19 and the time difference that the sound reaches to microphones 11 and 12 is calculated. A coefficient value is selected according to the time difference, and the selected coefficient value and the signal outputted from the bandpass filter group 15 are multiplied by a multiplier 21, and signals other than the object having large time difference are attenuated. The signal outputted from the multiplier of each frequency band is added by an adder 22, which reduces excess noise. Thus, a sound collection signal with the necessary frequency band can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound collecting device for collecting a sound signal with a microphone.

[0002]

2. Description of the Related Art In recent years, a camera-integrated video tape recorder has become widespread, and video and audio are often recorded. Although the object is recorded through the lens and the zoom is easy, the directional microphone is often used to record the sound, and directivity control is not easy. An example of controlling the directivity is shown, for example, in Technical Research Report EA89-92 of the Institute of Electronics, Information and Communication Engineers.

A directivity control device which is a conventional sound collecting device will be described below. FIG. 2 is a block diagram of this conventional directivity control device. In FIG. 2, reference numeral 1 denotes a plurality (23) of microphones, which are arranged in a line at intervals of 2 cm. Reference numeral 2 denotes a plurality of analog-digital converters (hereinafter referred to as ADCs) connected to the respective microphones 1, 3 denotes a plurality of digital filters to which respective output signals of the ADC 2 are input, and 4 denotes respective outputs of the digital filter 3. An adder 5 for adding signals, a digital-analog converter (hereinafter referred to as a DAC) 5 for converting the output signal of the adder 4 into an analog signal,
An output terminal 6 is connected to the DAC 5 and outputs the collected sound.

The operation of the directivity control device configured as described above will be described below.

The signal collected and output by the microphone 1 is converted into a digital signal by the ADC 2 and added to the digital filter 3. The respective output signals of the digital filter 3 are added by the adder 4, and then the DAC 5
Is converted back into an analog signal and output to the output terminal 6.
Here, the digital filter group 3 constitutes a two-dimensional digital filter. And each digital filter 3
By controlling the coefficient of and changing the sampling frequency of the digital circuit, it is possible to change the directional characteristics of the sound collected by the microphone 1.

[0006]

However, in the above-mentioned conventional structure, a large number of microphones and ADCs must be provided, and the digital filter 3 has a higher order (3).
Since a 0th order (Finite Impulse Response) FIR filter is used, there is a problem that the scale is large.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a sound collecting device which is small in scale and can collect a target sound.

[0008]

In order to achieve this object, a sound collector of the present invention includes two sets of band pass filter groups for separating an input signal into a plurality of frequency bands and a band pass filter group. A level detector group that detects the level of the output signal of the bandpass filter and an output signal of the pair of level detector groups connected to the bandpass filters of the same frequency band of the two sets of bandpass filter groups are stored. A signal processor group that calculates the time difference between the level change points output by the memory and each of the pair of level detectors from the stored contents of the memory, and selects and outputs a coefficient value according to the operation result, and one band pass filter group Each of the output signals of the respective frequency bands and the output signal of each of the signal processor groups, and an adder for adding the output signals of the multiplier groups.

[0009]

According to the present invention, with the above structure, the signals collected by the two microphones are input to the band pass filter groups and separated into the signals of the narrow frequency bands. Then, in the two kinds of bandpass filter groups, the level of the signal separated by the bandpass filter of the same frequency band is detected by the pair of level detectors, and the signals output by the pair of level detectors are stored in the memory. , Calculate the time difference of the level change point from the stored contents of the memory with the signal processor,
When the time difference increases, the coefficient whose value decreases from 1 is output to the multiplier. In the multiplier, the signal separated by the band pass filter is multiplied by the coefficient selected as described above. In this way, the same operation as described above is performed on the output signals of all the bandpass filter pairs, and the output signals of the multiplier group are added by the adder to be a signal in a wide frequency band. Here, the fact that there is no time difference between the level change points of the pair of level detectors indicates that the sound source exists at a position equidistant from the two microphones, and a large time difference means that the sound source moves away from the position. Indicates that. That is, the sound of the target sound source that is equidistant from the two microphones passes through, and the sound away from the target is attenuated. In this way, the target sound can be collected.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a sound collecting device according to an embodiment of the present invention. In FIG. 1, 11,1
2 is a microphone placed at a certain distance (for example, 20 cm), 13 and 14 are ADCs that convert the output signals of the microphones 11 and 12 into digital signals, and 15 and 16 are A
It is a group of band pass filters (hereinafter referred to as BPFs) that divides the output signals of the DCs 13 and 14 into frequency bands, and are composed of BPFs 151 to 15n and BPFs 161 to 16n, respectively. Reference numeral 17 is a first level detector for detecting the output signal level of the BPF 151, 18 is a second level detector for detecting the output signal level of the BPF 161, and 19 is an output of the first and second level detectors 17, 18. Signal is added,
The signal processor 21 stores the value in the memory 20, determines the time difference between the level change points, and outputs a coefficient according to the time difference. Reference numeral 21 denotes the output signal of the BPF 1151 and the signal processor 19.
, 22 is an adder to which the output signal of the multiplier 21 is added, 23 is a DAC for converting the output signal of the adder 22 into an analog signal, 24 is a DAC 2
3 is an output terminal for outputting the sound collection result obtained in 3.
Although not shown, BPFs 152 to 15n, BPFs
Also for 162 to 16n, BPF151, BPF16
Similar to the case of 1, it has an equivalent configuration for detecting the level of each output signal of the BPF group 15 and the BPF group 16 and performing multiplication. Therefore, the adder 22 has 1
~ N multiplication results have been added.

The operation of the sound collecting device of this embodiment having the above-described structure will be described below.

The signal obtained by the microphone 11 is A
It is converted into a digital signal at DC 13. The voice signal converted into the digital signal is the BPF in the BPF group 15.
It is divided into n series of frequency bands at 151 to 15n.
The audio signal obtained by the microphone 12 is also AD
It is divided into BPFs 161 to 16n in the BPF group 16 via C14. BPF1 through which signals in the same frequency band pass
The output signals of 51 and BPF 161 are applied to the first and second level detectors 17 and 18, respectively, and the average value of the signals is detected. The detected average value is used as the signal processor 19
Are stored in the area 1 and the area 2 of the memory 20, respectively. The signal processor 19 is
The change point of the value stored in the area 1 is detected, and the same pattern as the change point is searched in the area 2. When the same pattern is found, the time difference at which the change point is stored can be known from that location. Then, the coefficient value according to the time difference is selected from the read-only memory in the signal processor 19 and output. As the coefficient value, 1 is selected when the time difference is zero, and a value smaller than 1 is selected when the time difference is large. The coefficient value thus selected is added to the multiplier 21, multiplied by the output signal of the BPF 151, and the level is changed. Signal processor 19
Performs an operation of selecting a coefficient value when the output signal of the level detector 17 exceeds a certain set value, and when the level is less than or equal to the set value, the coefficient value retains the previous value. BPF1
The same signal processing as above is performed on the passing signals of 52 to 15n and BPFs 162 to 16n. The output signals of the n multipliers thus obtained are added by the adder 22, and the addition result is converted into an analog signal by the DAC 23 and output to the output terminal 24. BPF group 15 and BP
If there is no time difference between the level change points of the output signals of the F group 16, the signal source is an equal distance from the microphones 11 and 12, that is, the target sound source, and a large time difference means that the sound source is away from it. The sound output from the target sound source has a small coefficient output from the signal processor 19 and is attenuated in level by the multiplier 21. The signals obtained from the microphones 11 and 12 are BPF 151 to 1
5n, BPF 161 to 16n (for example, 32
However, even if a sound other than the target sound is input, if the frequency band is different, the coefficient selected by the signal processor 19 of the frequency band through which the target sound passes does not change, and the sound collection level is It doesn't change. In addition, a coefficient smaller than that coefficient is not selected for a few seconds (for example, 5 seconds) after a certain coefficient is selected to prevent a change in the audio level. Since the adders 22 add the signals of all the divided frequency bands, a sound collection signal in which the unintended signals are attenuated is obtained. When the signal processor 19 selects the coefficient value according to the time difference, the sound collection characteristic of the target sound can be changed by slightly modifying the coefficient value.

In the embodiment, the example in which the sound source equidistant from the two microphones 11 and 12 is used as the target sound source has been described. However, the level change points from the level signals stored in the areas 1 and 2 of the memory 20 are changed. When obtaining the time difference between the microphones 11 and 12, the time difference corresponding to the time when the sound is transmitted between the microphones 11 and 12 is provided as an offset value, and the offset value is subtracted from the time difference.
The target sound source may be arranged on the line connecting the lines 12 and 12. Also, the BPF groups 15 and 16 and the A connected to them.
Since the DC, the level detector group, the signal processor group, the multiplier group, etc. can be configured by using one digital signal processor in a time division manner, the circuit scale does not increase.

[0015]

As described above, according to the present invention, two sets of band pass filter groups, level detector groups for detecting the signal levels of the band pass filter groups, and level change points output by a pair of level detectors are provided. A signal processor group that calculates the time difference and selects a value according to the time difference, a multiplier group that multiplies the output signal of the band pass filter group and the coefficient value output from the signal processor group, and the output signal of the multiplier group By adding an adder to add the input signal, it is possible to detect the arrival time difference of the undesired audio signal, select a small coefficient value, and multiply it with the input signal to attenuate the level. Can be collected.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a sound collecting device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional directivity control device.

[Description of Codes] 1, 11, 12 Microphones 2, 13, 14 Analog-digital converter 3 Digital filter 4, 22 Adder 5, 23 Digital-analog converter 6, 24 Output terminal 15, 16 Band pass filter group 17 , 18 Level detector 19 Signal processor 20 Memory 21 Multiplier

Claims (1)

[Claims] 1. A first and a second band pass filter group having equivalent characteristics for separating two types of input signals into a plurality of frequency bands, and each of the first and second band pass filter groups. A level detector group for detecting the level of the output signal of the band pass filter; and a pair of the level detector groups connected to the band pass filters of the same frequency bands of the first and second band pass filter groups, respectively. A memory for storing the output signal; and a signal processor group for calculating the time difference between the level change points output by each of the pair of level detectors from the stored contents of the memory, and selecting and outputting a coefficient value according to the calculation result. A multiplier group for multiplying an output signal of each frequency band of the first band pass filter group and an output signal of each of the signal processor groups, and an output signal of the multiplier group. Pickup apparatus comprising an adder for adding.