JPH03226200A - Camera integration type video tape recorder - Google Patents

Abstract

PURPOSE:To record an audio signal with high quality by correcting a frequency characteristic of a noise signal at an adaptive filter circuit and subtracting the corrected signal from the audio signal. CONSTITUTION:The above recorder is provided with a noise use microphone 7, an audio signal microphone 3, analog digital conversion circuits 12, 10, an adaptive filter circuit 16 switching the characteristic based on an audio output signal SDOUT to correct the frequency characteristic from a digital noise signal SDN and a subtraction circuit 16 subtracting an output signal (y) of the adaptive filter circuit 18 from the digital audio signal SDO and outputting the audio output signal SDOUT. Thus, the output signal (y) of the adaptive filter circuit 16 whose characteristic is switched based on the audio output signal SDOUT is subtracted from the digital audio signal SDO to output the audio output signal SDODT, then the noise mixed in the digital audio signal SDO is suppressed. Thus, the audio signal is recorded with high quality.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a camera-integrated video tape recorder, and is particularly suitable for application to a small-sized camera-integrated video tape recorder.

B. Summary of the Invention The present invention enables a camera-integrated video tape recorder to record an audio signal with high quality by removing noise components from the audio signal using an adaptive filter.

C. Conventional technology Conventionally, in camera-integrated video tape recorders,
It is possible to record audio signals with high quality by effectively avoiding the mixing of noise.

In other words, in a camera-integrated video tape recorder, it is inevitable to avoid noise from the rotating drum, magnetic tape running system, etc. during recording, and therefore, there is a risk that the noise will be mixed into the audio signal and the quality of the audio signal will deteriorate. There is.

For this reason, for example, by housing the microphone in a housing via a damper or the like, vibrations directly propagating from the housing to the microphone are reduced and noise is prevented from entering the microphone.

D Problems to be Solved by the Invention However, when a microphone is housed in a housing via a damper etc., it is difficult to deal with relatively low frequency mechanical vibrations.
It becomes difficult to effectively reduce vibration propagation.

Furthermore, there is a characteristic that it is impossible to prevent noise from being mixed in at all with respect to noise radiated to the outside of the housing.

Particularly in miniaturized camera-integrated videotape recorders, the microphone and the noise source can be placed close to each other, so noise contamination can be avoided in this case, and it is possible to record audio signals with high quality. There was no problem.

As one way to solve this problem, for example,
As proposed in No. 2-230278, a method of arranging two microphone units so as to cancel out mechanical vibrations and configuring a microphone with the two microphone units can be considered.

According to this method, vibrations directly propagated to the microphone can be efficiently reduced.

However, this method also has the characteristic that it cannot prevent noise from being mixed in at all with respect to noise radiated to the outside of the housing.

On the other hand, a method of suppressing the noise component mixed into the audio signal using a filter circuit or the like may be considered.

However, since the noise from the rotating drum is superimposed on the frequency band of the audio signal and is distributed in a frequency range of several hundred to several thousand (Hz), it is impossible to suppress just the noise component even if a filter circuit is used. It was difficult to record the audio signal with high quality.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a camera-integrated video tape recorder that can record audio signals with high quality.

E Means for Solving the Problem In order to solve this problem, in the present invention, a noise microphone 7 is provided near the drive system 5, which collects the noise of the drive system 5 and outputs a noise signal SN. and an audio microphone 3 that collects audio and outputs an audio signal So.
and an analog-to-digital conversion circuit 12. which converts the noise signal SN and audio signal S0 into digital signals and outputs a digital noise signal S□ and a digital audio signal SDO.
10, and an audio output signal S. . , an adaptive filter circuit 16 that corrects the frequency characteristics of the digital noise signal SDH by switching its characteristics based on , and the digital audio signal SIO.
fi&X the output signal y of the adaptive filter circuit 16 from
The subtraction circuit 18 outputs the audio output signal SDOllT.

By subtracting the output signal y of the adaptive filter circuit 16 whose characteristics are switched based on the F-action audio output signal S DOUT from the digital audio signal SD0 and outputting the audio output signal 5tlotIT, noise mixed in the digital audio signal SDO can be suppressed. be able to.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, 1 generally indicates a camera-integrated video tape recorder, and an image captured through a lens 2 is recorded by the built-in video tape recorder.

For this reason, in the camera-integrated video tape recorder 1, a microphone 3 for collecting audio (hereinafter referred to as an audio microphone) is arranged near the lens 2, facing the subject.

Furthermore, in the camera-integrated videotape recorder 1, a microphone 7 for collecting noise (hereinafter referred to as a noise microphone) is arranged near the rotating drum 5, and the noise microphone 7 generates noise emitted from the rotating drum 5. It is designed to faithfully collect sound.

As a result, as shown in FIG. A noise signal SN consisting of the noise of the drum 5 can be obtained.

Analog-to-digital conversion circuits (A/D) 10 and 12 convert the audio signal S0 and the noise signal SN into digital signals, respectively, and produce a digital audio signal SOO and a digital noise signal S. Output.

The adaptive noise canceller 14 receives the digital noise signal SI
To suppress the noise component mixed into the digital audio signal SDO using N as a reference.

That is, the adaptive noise canceller 14 provides the digital noise signal S to the adaptive filter circuit 16 and outputs its output signal to the subtraction circuit 18.

Furthermore, the adaptive noise canceller 14 inputs the digital audio signal S to the fiX circuit 18. is given, and the audio output signal Sゎ is output from the subtraction circuit 18. at is output to a recording system signal processing circuit via a digital-to-analog conversion circuit (D/A) 20, and is also fed back to the adaptive filter circuit 16.

The adaptive filter circuit 16 has an F I R (finite
ts+pulse response) type filter circuit, and when recording starts, the audio output signal S11°U?
, thereby switching the characteristics based on the audio output signal Sl,. The noise component contained in a7 is suppressed.

At this time, the adaptive filter circuit 16 detects a period in which the signal level of the digital audio signal SDO is below a predetermined level based on the signal level detection result of the digital audio signal S0° output from the signal level detection circuit 19.

As a result, the adaptive filter circuit 16 is in a state where the subject's voice is not included in the digital audio signal sDa, that is, the digital audio signal S. 1, which contains only the noise of the rotating drum 5! (hereinafter referred to as the silent state), and when recording starts, the audio output signal S DOU is output in the silent state.
The characteristics are switched so that the average value power of T becomes 0 level.

Further, the adaptive filter circuit 16 receives the audio output signal S. u
If we can obtain the characteristic that the average power of T becomes 0 level,
The characteristics at this time are held, and the frequency characteristics of the digital noise signal SDH are corrected and output using the characteristics.

That is, as shown in FIG. 3, the adaptive filter circuit 16 includes delay circuits 22 (N-1) and 22 (N-1) connected in series.
2), ..., 22 (0) is given the digital noise signal SDN, and the digital noise signal Sゎ and each delay circuit 22 (N-1), 22 (N-2), ...・・・
The output signal of 22 (0) is multiplied by the multiplier circuits 24 (N), 24
(N-1), 24 (1), 24 (
0) in an adder circuit 26.

Here, delay circuits 22 (N-1), 22 (N-2),
. . . , 22 (0) are selected such that their respective delay times coincide with the clock period of the digital noise signal S□.

Therefore, the digital noise signal S. When the value of is expressed as XN, each delay circuit 22 (N-1), 22 (N-2), . . .
. . , 22(0) output signals each have 1
Value delayed by sample lN-1% lN-1,...
..., X, delayed signals can be obtained.

Therefore, multiplier circuits 24 (N), 24 (N-1), . . .
..., 24 (1), 24 (0) multiplication value is ho
, hI, .

On the other hand, multiplier circuits 24 (N), 24 (N-1
), ..., 24 (IL 24 (0) is the silent state at the start of recording, L M S (least m
The multiplication value +ho, hl, ......, hN-, hs can be switched using the ean 5quear) algorithm, and as a result, the average power of the audio output signal S0°LIT becomes 0 level in a silent state. Switch the characteristics so that

That is, the multiplication value at sample time n is, hI, .
..., hll-1,, hN as h 11 (1%)
,hl(.

・・・・・・ hN−□nl h N ++a),
Value of delayed signal χ8-0, xN-+, """, Xo @
X)l-11R)%
(nl), the multiplication value h and (7, 1) are sequentially updated so as to satisfy the following formula %() (2).

Here, μ is a value expressed by the following equation using the maximum eigenvalue λXAI of the correlation matrix of the input digital noise signal SIN.

In this way, the multiplication value hi(
By updating lI+I+, the average power e of the audio output signal s_oua can be converged to the O level in a period of several hundred [m5ec].

At this time, in the adaptive filter circuit 16, the power X value hi (Rol) is updated in a silent state, so that the digital audio signal S,. can maintain the signal level at 0 level.

Therefore, if the adaptive filter circuit 16 maintains this characteristic, the digital audio signal S. Even if the subject's voice is included in the digital audio signal S,.

Suppresses the noise component mixed into the audio output signal S Dol
l? can be output.

Therefore, by outputting the audio output signal Soouy to the recording system via the digital-to-analog conversion circuit 20, -
The noise that is emitted from the housing and then enters through the audio microphone 3 can be effectively suppressed, and audio can be recorded with high quality.

By the way, instead of suppressing the noise mixed into the audio signal by converting it into a digital signal as described above, it is conceivable to configure the entire audio signal with an analog circuit.

However, this type of camera-integrated videotape recorder 1 has a feature that the frequency characteristics of noise differ from device to device.

Furthermore, the noise itself is characterized by a wide frequency band.

Therefore, if the entire system is constructed from analog circuits, the adjustment work will be complicated and it will be difficult to practically apply it to the camera-integrated video tape recorder 1.

However, as in this embodiment, L is turned off in the silent state when recording starts.
By switching the characteristics of the adaptive filter circuit 16 using the MS algorithm, it is possible to reliably suppress noise with a wide frequency band even if the frequency characteristics of noise differ from device to device.

Furthermore, this type of camera-integrated video tape recorder 1 has a characteristic that the frequency characteristics of the noise change as the device ages.

Therefore, if the characteristics of the adaptive filter circuit 16 are set only once, the noise suppression effect will decrease as the equipment ages.

However, as in this embodiment, if the characteristics of the adaptive filter circuit are switched each time in the silent state when recording starts, noise can be reliably suppressed even if the equipment changes over time.
You can always record high quality audio.

In the above configuration, the audio signal output from the audio microphone 3 is converted into a digital audio signal S by the analog-to-digital conversion circuit 10. After being converted to 0, it is output to the signal level detection circuit 9, where the digital audio signal 50
A signal level of 0 is detected.

The signal level detection result is output to the adaptive filter circuit 16, whereby the adaptive filter circuit 16 detects a silent state at the start of recording.

In this silent state at the start of recording, the adaptive filter circuit 16 uses the LMS algorithm to output the audio output signal 5DOL.
The characteristics are switched so that the average value power of IT becomes O level, thereby correcting the frequency characteristics of the digital noise signal SDH output to the subtraction circuit 18, and the audio output signal S
Suppresses noise components mixed into oouy.

As a result, via the digital-to-analog conversion circuit 2o,
It is possible to obtain an audio signal that is free from noise.

According to the above configuration, the frequency characteristics of the noise signal obtained through the noise microphone are corrected by the applied filter circuit, and then subtracted from the audio signal obtained through the audio microphone, so that the noise is suppressed. It is possible to obtain signals and record audio signals with high quality.

In the above-described embodiment, a case has been described in which the signal level detection circuit detects the signal level of a digital audio signal to detect a silent state, but the present invention is not limited to this.
For example, when recording starts, the characteristics of the adaptive filter circuit may be switched in a quiet place.

Further, in the above-described embodiment, a case was described in which the adaptive filter circuit was configured with an FIR type filter circuit, but the present invention is not limited to this.
The adaptive filter circuit may be configured with an impulse response type filter circuit or a lattice type filter circuit.

Further, in the above-described embodiment, a case has been described in which the characteristics of the adaptive filter circuit are switched using the LMS algorithm, but the present invention is not limited to this, and various methods such as the fixed learning method can be widely applied.

Furthermore, in the above embodiment, a case was described in which the noise of a rotating drum was detected using a noise microphone.
In the present invention, instead of this, detection may be performed using a vibration detector.

Further, in the above-described embodiment, the case where the noise generated from the rotating drum is suppressed has been described, but the present invention is not limited to this. For example, the present invention is also applicable to the case where the noise generated from the magnetic tape running system and the zoom drive system is also suppressed. etc. can be widely applied.

In this way, it is possible to suppress the noise of the magnetic tape running system, which varies depending on the magnetic tape, and the noise generated when driving the zoom lens.

Effects of the Invention As described above, according to the present invention, by correcting the frequency characteristics of the noise signal using an adaptive filter circuit and then subtracting it from the audio signal, the noise signal mixed into the audio can be suppressed.
A camera-integrated videotape recorder capable of recording audio signals with high quality can be obtained.

[Brief explanation of drawings]

3 is a block diagram showing an audio signal processing circuit, and FIG. 3 is a block diagram showing an adaptive filter circuit. 1... Camera-integrated videotape recorder, 3
...Sound microphone, 5...Rotating drum, 7...Noise microphone, l0
112...Analog-digital conversion circuit, 16
...Adaptive filter circuit, 18...Subtraction circuit.

Claims (1)

[Scope of Claims] A noise microphone disposed near a drive system, which collects noise from the drive system and outputs a noise signal; an audio microphone which collects sound and outputs a sound signal; an analog-to-digital conversion circuit that converts the noise signal and the audio signal into digital signals and outputs the digital noise signal and the digital audio signal; and an analog-to-digital conversion circuit that converts the noise signal and the audio signal into digital signals and outputs the digital noise signal and the digital audio signal, and switches the characteristics based on the audio output signal and corrects the frequency characteristics of the digital noise signal. A camera-integrated video tape recorder comprising: an adaptive filter circuit; and a subtraction circuit that subtracts the output signal of the adaptive filter circuit from the digital audio signal and outputs the audio output signal.