JPH06319193A - Video camera containing sound collector - Google Patents

Abstract

PURPOSE:To prevent both high and low frequency band component level detectors from detecting the erroneous levels due to the variance of the center potential of each filter output. CONSTITUTION:A high frequency band component level detector 14 and a low frequency band component level detector 15 detect the high and low frequency band component levels of the output of a microphone 1 via an HPF 2 and an LPF 3 respectively. Then a sound collector detects the generation of wind noises based on the levels detected by both detectors 14 and 15 and then attenuates the low frequency band component when the wind noises are generated. In such a constitution, the output of the microphone 1 is supplied to a mute circuit 22 only for a certain period of time after the power source is supplied to a system. Thus the AC component is eliminated out of the output of the microphone 1, and this output is inputted to the filters 2 and 3. Then the center potential of each filter output is stored in a reference potential memory. The output of the microphone 1 is directly inputted to both filters 2 and 3, and the center potential stored in the memory is subtracted from the detection output of each filter. These subtraction outputs are defined as the high and low frequency band component levels.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera equipped with a sound pickup device having a wind noise suppressing function.

[0002]

2. Description of the Related Art A problem with recording with a video camera is that the recording quality is extremely deteriorated due to wind noise during outdoor shooting. Therefore, conventionally, various proposals have been made regarding the method of suppressing the wind noise. Generally, for example, JP-A-64-20798 (H04R3 / 0)
As shown in 0), a method of comparing the high frequency band component and the low frequency band component of the microphone output and automatically controlling the sensitivity of the low frequency band based on the comparison result is used. ing.

The conventional technique will be described below.
In FIG. 5, 1 is a microphone and 2 is a microphone 1.
High-pass filter (HPF) for extracting the high-frequency component of the output of the, 3 is a low-pass filter (LPF) for extracting the low-frequency component of the output of the microphone 1, 4 is the HPF
High-frequency level detection unit for detecting output level, 5 is LPF
Low-frequency level detection unit for detecting output level, 6 is HPF
From the output and the LPF output, a determination unit that determines whether the output of the microphone 1 is a voice signal or wind noise, 7 is an attenuator that controls the gain of the LPF output by the determination unit 6, and 8 is the output of the HPF 2 and the output of the attenuator 7. Adder for adding and, 9 is adder 8
It is an output terminal for outputting the output to the recording unit in the subsequent stage.

Next, in FIG. 6, AU is the spectrum of the output signal of the microphone 1 when voice is input, and N is the spectrum of the output signal of the microphone 1 when wind noise is input.
From the comparison between spectrum AU and spectrum N in FIG. 6,
It can be seen that the wind noise spectrum is concentrated in the low frequency band. Therefore, in order to determine whether the output of the microphone 1 is a regular voice signal or wind noise, the frequency spectrum of the signal may be examined.

In this prior art, the microphone 1
The HPF2 and the LPF3 separate the output of the high frequency signal and the low frequency signal. The signals in the two frequency bands are input to the high band level detection unit 4 and the low band level detection unit 5, and the levels of the respective frequency band signals are detected. These two signal levels are input to the determination unit 6, and when the level of the low frequency signal is much higher than the level of the high frequency signal, it is determined to be wind noise. That is, when the value obtained by dividing the level of the low frequency signal by the level of the high frequency signal is less than or equal to a preset threshold value, it is determined as an audio signal, and when the value is greater than or equal to the threshold value, it is determined as wind noise.

Next, a determination signal indicating the above determination result is supplied to the attenuator 7, and the attenuation amount of the attenuator 7 is controlled. That is, the attenuator 7 outputs the LPF 3 output to the adder 8 without attenuating when the wind is weak, that is, when the determining unit 6 determines that wind noise does not occur, and when the wind is strong, that is, the determining unit 6 When it is determined that wind noise is occurring, L
The output of PF2 is attenuated by a predetermined amount and output to the adder 8.

In the adder 8, the output of the HPF 2 and the output of the attenuator 7 are added and output to the output terminal 9, so that the signal derived at the output terminal 9 can suppress the influence of wind noise.

[0008]

By the way, in the prior art, as a means for detecting the level of each frequency band component in the high-frequency level detecting section 4 and the low-frequency level detecting section 5, the following method is generally used. Can be considered.

FIG. 7 shows the details of the high frequency level detecting section 4. Reference numeral 4a is a detection circuit for detecting the input signal, 4b is a reference potential memory in which a value considered to be the central potential of the output signal amplitude of the HPF 2 is stored in advance, 4c
Is a subtractor for calculating the difference between the output of the detection circuit 4a and the reference potential.

Next, the manner of signal processing in the high frequency level detecting section 4 will be described with reference to FIG. HP shown by the chain line in FIG.
When the output signal SH of F2 is input to the detection circuit 4a and subjected to envelope detection processing, the detection signal Ha shown by a solid line is generated.
Becomes This detection signal Ha is input to the subtractor 4c, and the timing Tn (n = 1, 2,
3, ...), the potentials V1, V2, V of the detection signal Ha
3, that is, the difference VD between the Vn and the reference potential Vr stored in the reference potential memory 4b, VD1, VD2, VD3 ,.
.. That is, VDn is calculated and sequentially sent to the determination unit 6 in the subsequent stage. That is, VDn = Vn-Vr is established. On the other hand, the low-frequency level detecting section 5 is similarly configured and shows the same signal processing form.

Here, as the reference potential Vr, a center potential of the output signal amplitude of the HPF 2, that is, a constant value which is theoretically considered to be a DC component of the output signal is stored in advance. However, the actual center potential often shows a value different from the theoretical value due to the individual difference of the components forming the circuit, the temperature characteristic, and the like. This point will be described with reference to FIGS. 9 and 10.

9 and 10 show two circuits in which the actual center potential of the output signal of the HPF 2 is different from Vr 'and Vr ".
It shows a case where signals of the same amplitude are input. First, in FIG. 9, when the detection signal Ha at a certain timing Tn is Ha ′, this level is Vn ′, which is the reference potential Vr stored in the reference potential memory 4b.
The difference VDn ′ from Vdn ′ is VDn ′ = Vn′−Vr.
Further, in FIG. 10, when the detection signal Ha at a certain timing Tn is Ha ″, this level is Vn ″, and the difference VDn ″ from the reference potential Vr is VDn ″ = V.
n ″ -Vr.

As is clear from the comparison between VDn 'in FIG. 9 and VDn "in FIG. 10, even when signals of the same amplitude, such as Ha' and Ha", are input, variations in the center potential are actually observed. Therefore, the signal level to be judged differs greatly. On the other hand, the same problem can be considered in the low frequency level detection unit 5.

Therefore, since the center potential varies, the high-frequency and low-frequency component levels of the audio signal input from the microphone 1 cannot be accurately detected, and the original characteristics cannot be sufficiently obtained. Occurs.

[0015]

The present invention is directed to a microphone, an HPF for extracting a high frequency component of the output of the microphone, an LPF for extracting a low frequency component of the output of the microphone, and a DC component of a high frequency signal. A high-frequency level detection unit that detects the amplitude from the high-frequency signal level,
A low-frequency level detection unit that detects the amplitude from the DC component of the low-frequency signal as a low-frequency signal level, and a determination unit that determines whether the microphone output signal is a voice signal or wind noise based on the high-frequency and low-frequency signal levels. And an attenuator that outputs the LPF output signal after attenuating it when the determination unit determines that it is noise, and outputs it without attenuation when it determines that it is a voice signal.
A high-frequency signal and a low-frequency signal are provided by including an adder that adds the output of the HPF and the output of the attenuator to the outside and removes the AC component of the microphone output for a certain period of time and reads only the DC component during this period. It is characterized in that the reference position of is corrected to an appropriate value at any time.

[0016]

Since the present invention is configured as described above, it is possible to accurately detect the frequency component levels of the high frequency band and the low frequency band of the voice signal input from the microphone, and to realize a more accurate wind noise suppression function. be able to.

[0017]

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 circuit block diagram of a sound collecting device mounted on a video camera according to this embodiment. It should be noted that the same parts as those in FIGS. 5 and 7 showing the prior art are designated by the same reference numerals and the description thereof will be omitted.

Compared with the circuit block of the prior art, a switch circuit 21 and a mute circuit 22 are inserted between the microphone 1 and the HPF2 and LPF3, and a timer circuit 20 is added, so that a higher frequency band than the output of the timer circuit 20 can be obtained. It is configured so that the operations of the low-frequency level detection units 14 and 15 are controlled. That is, 20 is a timer circuit that is activated by receiving a signal that the power of the sound collecting device of the video camera is turned on, and switches the level of the control signal that is an output when a preset predetermined time is reached. Microphone 1
A switch circuit that receives the control signal from the timer circuit 20 as an input and selectively switches to the fixed contacts 21a and 21b, and 22 is a mute circuit that removes the AC component of the microphone 1 output derived to the fixed contact 21a. Is.

Details of the timer circuit 20 will be described with reference to FIG. When the sound collecting system including all the components of FIG. 1 is powered on, the POWER signal changes from the L (low) level to the H (high) level. In the timer circuit 20, the edge detector 20a receives this POWER signal,
Only when the POWER signal changes from L level to H level, a pulse is issued to the counter 20b in synchronization with this rising edge.

When the counter 20b receives this pulse,
This is used as a reset signal, the value held internally until then is reset, and the count-up of a constant frequency clock generated from an oscillator (not shown) is started.

This count value t is always input to the first count comparator 20e and the second count comparator 20f.
When the power is turned on, both the first count comparator 20e and the second count comparator 20f output the control signal S1 of L level,
S2 is output.

Here, first, the first count comparator 20e compares the input count value t with the first count threshold Ca stored in advance in the first count threshold memory 20c. Then, the count value t is the first count threshold Ca
While it is less than the above, the L-level control signal S1 is continuously output, and when the count value t eventually becomes equal to or larger than the first count threshold value Ca, the control signal S1 is switched to the H level.

Similarly, the second count comparator 20f also inputs the count value t and the second count threshold memory 20 in advance.
The second count threshold Cb stored in d is compared. While the count value t is less than the second count threshold value Cb, the L-level control signal S2 is continuously output, and when the count value t becomes equal to or more than the second count threshold value Cb, the control signal S2 is set to the H level. Switch. Here, both count thresholds have a relationship of Ca <Cb, and specifically, the time ta required until the count value t reaches the first count threshold Ca reaches 1 second, and also reaches the second count threshold Cb. Both thresholds are set such that the time tb required for the time is approximately doubled to 2 seconds. That is, the control signal S1 is L → H
The level becomes the time ta after the power is turned on, and the control signal S2 becomes the L → H level at the time tb after the power is turned on.

Next, the switch circuit 21 will be described. The switch circuit 21 controls the control signal S2 from the timer 20.
The control signal S2 is on the fixed contact 21a side while the control signal S2 is at the L level and guides the output signal of the microphone 1 to the mute circuit 22 (first mode). When the control signal S2 eventually becomes H level, the switch circuit 21 is switched to the fixed contact 21b side to directly guide the output signal of the microphone 1 to the HPF 2 and the LPF 3 (second mode). The mute circuit 22 removes the AC component of the audio signal output from the microphone 1 and allows passage of only the DC component.

Next, the high band level detecting section 14 to which the HPF2 output and the control signal S1 are input and the low band level detecting section 15 to which the LPF3 output and the control signal S1 are input will be described with reference to FIG.

The high-frequency level detecting section 14 is the same as the high-frequency level detecting section 4 shown in FIG.
e is added, and the reference potential memory 4f has a fixed reference potential Vr set in advance as shown in 4b of FIG.
Is not stored, but the output of the detection circuit 4a input via the switch 4e is stored as a reference potential. Timer 2
The control signal S1 output from 0 outputs a pulse to the switch circuit 4e in synchronization with this rising edge only when the edge detector 4d changes the control signal S1 from the L level to the H level.

The switch circuit 4e is inserted between the detection circuit 4a and the reference potential memory 4f, and when receiving this pulse,
That is, when the output of the edge detector 4d is at the H level, it is closed to allow passage of the detection output Ha of the detection circuit 4a to the reference potential memory 4f, and the detection output immediately after this passage is stored in the reference potential memory 4f as the reference potential Vr. It

On the other hand, the low-frequency level detecting section 15 is also the detection circuit 1
The signal input to 5a is an LPF instead of the HPF2 output.
Except for having three outputs, it has the same configuration as the high frequency level detecting section 14 and performs the same operation. That is, the edge detection circuit 15d that receives the control signal S1 and emits a pulse, the switch circuit 15e that closes only during the H period of this pulse, the detection circuit 15a that detects the LPF output, and the reference potential memory 15f that stores the output of the switch circuit 15e as the reference potential. , A subtractor 15c for subtracting the reference potential of the reference potential memory 15f from the output of the detection circuit 15a.

Timer circuit 2 configured as described above
0, the switch circuit 21, and the mute circuit 22, the state of the signal guided to the high-frequency and low-frequency level detection units 14 and 15 will be described with reference to FIG.

From when the power is turned on until the count value t of the counter 20b reaches the second count threshold value Cb, the switch circuit 21 guides the output signal of the microphone 1 to the mute circuit 22 by the control signal S2. The AC component is removed, and the DC component, that is, the center potential of the amplitude of the signal is input to the high band and low band level detection units 14 and 15.

In the high frequency level detector 14, the control signal S1
In response to the action of the edge detector 4d and the switch circuit 4e, the first mode is set in the first mode from when the power is turned on to when the count value t of the counter 20b reaches the first count threshold value Ca, that is, half of the time tb. The potential after the passage of time is stored as Vr in the reference potential memory 4f.
On the other hand, the low-frequency level detecting section 15 also stores the reference potential in the same manner.

Next, when time tb elapses after the power is turned on, the second mode is set, and the output of the microphone 1 is directly input to the HPF 2 and the LPF 3, and the detection circuits 4a and 15 are provided.
a, the reference potentials stored in the reference potential memories 4f and 15f are detected by the subtracter 4 from the detected outputs.
Subtraction is performed at c and 15c, and the subtracted outputs are input to the determination unit 6 as high frequency component and low frequency component levels, respectively. still,
The pulses from the edge detectors 4d and 15d are
The pulse width is set so as to return to the L level by the time tb, and the switch circuits 4e and 15e are open when the time tb has elapsed.

As described above, each time the power is turned on, the center potential of the input signal immediately after the power is turned on, that is, when the minute time ta has passed after the power is turned on, is newly used as the reference potential in each reference potential memory 4f. It is stored in 15f. By making the reference potential variable according to the variation of the central potential in this way,
As shown in FIGS. 9 and 10, the difference between the level of the detection signal and the reference potential is always constant at Vd when a signal having the same amplitude is input.

The respective outputs from the high band and low band level detecting sections 14 and 15 are inputted to the judging section 6 as high band and low band frequency component levels, respectively, where the same judgment operation as in the conventional example is performed. Further, when the determination unit 6 recognizes that it is wind noise, the attenuator 7 attenuates the LPF3 output by a predetermined amount, the attenuator 7 output and the HPF2 output are added by the adder 8, and the result is output to the output terminal 9. By doing so, the microphone output obtained at the output terminal 9 is not affected by wind noise. It goes without saying that the operation of each circuit described above can be processed by software using a microcomputer.

[0036]

As described above, according to the present invention, the frequency component levels of the high frequency band and the low frequency band of the audio signal input from the microphone are accurately detected without being affected by the variation in the center potential of the HPF and LPF outputs. Therefore, the wind noise suppressing function with higher accuracy can be realized.

[Brief description of drawings]

FIG. 1 is an overall circuit block diagram of an embodiment of the present invention.

FIG. 2 is a circuit block diagram of a main part of an embodiment of the present invention.

FIG. 3 is a circuit block diagram of a main part of an embodiment of the present invention.

FIG. 4 is a diagram showing the timing of setting the center potential when the power is turned on in the embodiment of the present invention.

FIG. 5 is a circuit block diagram of a conventional example.

FIG. 6 is a diagram showing a spectral distribution when wind noise is input and when a voice signal is input.

FIG. 7 is a circuit block diagram of a main part of a conventional example.

FIG. 8 is a diagram illustrating a level detection method.

FIG. 9 is a diagram illustrating a level detection result due to variations in center potential.

FIG. 10 is a diagram illustrating a level detection result due to variations in center potential.

[Explanation of symbols]

 1 Microphone 2 HPF 3 LPF 22 Mute circuit 21 Switch circuit 4a Detection circuit 15a Detection circuit 4f Reference potential memory 15f Reference potential memory 4c Subtractor 15c Subtractor 6 Judgment unit 7 Attenuator 8 Adder

Claims (1)

[Claims] 1. A microphone, a high-pass filter for extracting a high-frequency component of an input signal, a low-pass filter for extracting a low-frequency component of an input signal, and an AC component of an input signal is removed for a certain period of time. Alternating current removing means, selecting means for inputting the microphone output to both filters through the alternating current removing means in the first mode, and directly inputting the microphone output for both filters in the second mode, and the selecting means Switching control means for switching to the second mode after being set to the first mode for a certain period of time, and a first for performing envelope detection of the output of the high-pass filter.
Detection means, first reference potential storage means for storing the output level of the first detection means as a first reference potential in the first mode, and first output from the output of the first detection means in the second mode.
First subtraction means for reducing the reference potential and outputting it as a high frequency component level; and second for performing envelope detection of the output of the low-pass filter.
Detection means, second reference potential storage means for storing the output level of the second detection means as a second reference potential in the first mode, and second output from the output of the second detection means in the second mode.
Second subtracting means for subtracting the reference potential and outputting as a low frequency component level; determining means for determining whether the microphone output is an audio signal or wind noise based on the high frequency component level and the low frequency component level; A video including a sound collecting device having an attenuating means for attenuating the low-pass filter output when the microphone output is determined to be wind noise by the determining means, and an adding means for adding the high-pass filter output and the attenuating means output. camera.