JPH08153365A - Magnetic recorder with built-in microphone - Google Patents

Abstract

PURPOSE: To eliminate a noise due to a beat sound of a tape when the volume of a built-in microphone is a small level and to invalidate filter operation when a large level and to prevent tone quality from being impaired by providing a level detection circuit, a comparison circuit and a switch, etc. CONSTITUTION: A trap circuit 2 reduces a frequency component in the vicinity of a frequency band among which the beat sound of the tape distributes from a sound signal from the built-in microphone 1, and the switch 3 selects alternatingly the sound signal from the built-in microphone 1 and the sound signal from the trap circuit 2. The comparison circuit 6 compares the level of the sound signal detected by the level detection circuit 5 with a prescribed reference level, and switch controls the switch 3 according to the comparison result. That is, when the sound from a subject is small, and the level of the sound signal is lower than the reference level, the switch 3 is switched to a fixed contact 3b side, and when the sound from the subject is high, and the level of the sound signal exceeds the reference level, the switch 3 is switched to the fixed contact 3a side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a microphone (hereinafter referred to as
And a VTR unit for recording video and audio signals formed by the camera unit on a magnetic tape, which are integrated with each other.

[0002]

2. Description of the Related Art In a camera-integrated VTR such as an 8 mm camcorder, noise generated by rotation of a cylinder around which a tape is wound, that is, a so-called tape tapping noise is picked up by a microphone, which is desired as annoying noise. Will be recorded on the tape together with the sound signal of.

Conventionally, in order to remove this noise, the frequency characteristics of the built-in microphone are lowered, or the sound signal component of the frequency at which the tape tapping sound is distributed is always dropped by a trap filter to reduce the tape tapping sound. It was

[0004]

The spectrum of the tapping sound itself is in the vicinity of 2 to 3 kHz, and it overlaps with a part of the audible band of the voice to be recorded. Inserting a trap filter for removing the frequency band component or reducing the frequency characteristics of the microphone inserts a filter in the audible band, and also impairs the sound quality of the sound originally recorded from the built-in microphone. Become.

[0005]

According to the present invention, there is provided a filter means for reducing a predetermined frequency band component of a first audio signal obtained from a built-in microphone and outputting it as a second audio signal.
A selection means for selectively selecting one of the first and second audio signals, a level detection means for detecting one level of both audio signals, a level detection means output is compared with a predetermined level, and a level detection means output Selection control means for causing the selecting means to select the first audio signal when the level exceeds the predetermined level, and outputting a selection control signal for causing the selecting means to select the second audio signal when the level of the output of the selecting means falls below the predetermined level. And a cylinder on which a magnetic tape is wound and a magnetic head for recording the output of the selecting means on the magnetic tape is mounted.

[0006]

Since the present invention is configured as described above, the band component in which the tape tapping sound is present only when the volume level of the sound picked up by the built-in microphone is low and the tape tapping sound becomes unpleasant. Is reduced, the noise due to the tape tapping sound is removed, and conversely, when the volume level is sufficiently high, the tape tapping sound removal operation is not performed,
Sound quality is not impaired.

[0007]

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 the device of this embodiment. In the figure, reference numeral 1 is a built-in microphone that is integrally mounted in advance on the camera-integrated VTR main body, and 2 is in the vicinity of 2.8 kHz, which is a frequency band in which the sound signal from the built-in microphone 1 is input and tape tapping sound is distributed. It is a trap circuit whose frequency characteristics are set so as to reduce frequency components. 3 is a fixed contact 3a to which a voice signal from the built-in microphone 1 is applied
And a switch for selectively selecting one of the fixed contacts 3b to which the audio signal passed through the trap circuit 2 is applied,
4 is an AMP that amplifies the audio signal output from the switch 3 by about 60 dB, 5 is a level detection circuit that detects the signal level of the AMP 4 output, 6 is the level of the audio signal detected by the level detection circuit 5 and a predetermined reference Level (eg -40
This is a comparison circuit for level comparison of dBs).
The comparison result at becomes a switch switching signal for switching control of the switch 3.

Next, a camera-integrated VT having the above structure
The operation of the audio signal processing circuit of the R body will be described. The audio signal picked up by the built-in microphone 1 is directly input to the fixed contact 3a as the first audio signal and also input to the trap circuit 2 to remove only the frequency band component in which the tape tapping sound is present and It is input to the fixed contact 3b as an audio signal.

Immediately after the power of the camera-integrated VTR main body is turned on, the switch 3 is switched to the fixed contact 3a side in the initial state to select the first audio signal, and this signal is AMP4.
Is amplified and level detected by the level detection circuit 5,
This detection output is compared with the reference level in the comparison circuit 6,
When the detection output exceeds the reference level, the sound from the subject desired to be recorded is loud, the first audio signal has a sufficient volume and a high level, and even if the volume is always small and a constant tapping sound is included. Assuming that the switch 3 is held on the side of the fixed contact 3a so as not to be offensive to the ears, an audio signal from which the tapping sound is not removed is retained from the AMP 4 so that the sound quality of the sound from the subject is not impaired. Is supplied to a magnetic head mounted on a rotary cylinder together with a video signal in a well-known recording system (not shown), and recorded on a magnetic tape wound around the cylinder.

When the sound from the subject is low and the level of the first sound signal is low and falls below the reference level, the comparison circuit 6 supplies the switch 3 with a switch changeover signal for selecting the fixed contact 3b. The switch 3 is switched to the fixed contact 3b side. Therefore, the switch 3 selects the second audio signal in which the frequency band component corresponding to the tapping sound is reduced in advance via the trap circuit 2, and while the audio from the subject is low, the second audio signal is selected. Is input to the recording system from the output terminal 8 and recorded on the magnetic tape.

Further, while the switch 3 is selecting the second audio signal, the level detection circuit 5 detects the level of the output of the switch 3, so that the level of the second audio signal is compared with the reference level. Therefore, when the sound from the subject becomes loud again, the detection level becomes louder, and a switch switching signal for switching the switch 3 to the fixed contact 3a side is issued above the reference level, so that the switch 3 is moved to the fixed contact 3a side. The first audio signal is selected by switching, and this is recorded.

Since the second audio signal has a reduced frequency band component in which the tapping sound is present compared to the first audio signal, the level detected by the level detection circuit 5 is slightly different from that of the second audio signal. However, since the band component to be removed is extremely small compared to the entire band of the audio signal, the difference in detection level is extremely small, and the reference level is used when determining whether the audio level from the subject is sufficiently high. There is no particular effect on the comparison result of. Further, the reference level is set to an optimum value in advance based on experiments.

As described above, the sound signal picked up by the built-in microphone 1 is small, and the tape tapping sound whose absolute level does not always change is relatively conspicuous and recorded as annoying noise. When there is a fear, by selecting the second audio signal with the switch 3, it is possible to prioritize the removal of the noise caused by the tapping sound over the sound quality of the audio signal from the subject.

Since the audio signal from the built-in microphone 1 of the AMP 6 is at a very small level, it is possible to avoid the possibility of being erroneously determined if the audio signal is directly input to the level detection circuit 5 and the comparison circuit 6. It is inserted as a purpose.

In the above-described embodiment, the AMP4 is arranged at the subsequent stage of the switch 3 and the output of the AMP4 is used as the input of the level detection circuit 5, but instead of this, the AMP4 is provided immediately after the built-in microphone as shown in FIG. The AMP4 output is directly applied to the fixed contact 3a of the switch 3, and at the same time the trap circuit 2
It is also possible to supply the AMP4 output to the level detection circuit 5 and input the AMP4 output to the level detection circuit 5. In such a configuration, the signal level-detected by the level detection circuit 5 is
It is possible to always output the first audio signal that does not pass through the trap circuit 2. Further, the input of the level detection circuit 5 in FIG. It is also possible that the signal to be reproduced is always the second audio signal. In any case, there is no change in that the switch 3 selects the first audio signal when the detection level in the level detection circuit 5 exceeds the reference level, and the second audio signal is selected when the detection level falls below the reference level.

[0016]

As described above, according to the present invention, when the volume level of sound picked up by the built-in microphone is so low that the tapping sound is unpleasant to the ear, the frequency band component of the tapping sound is removed by the filter operation. The noise caused by tapping the tape is removed, and when the volume level that is picked up is large enough not to be offensive to the ear, the filter operation may be disabled and a specific band of the audio signal may be removed, impairing the sound quality. Absent.

[Brief description of drawings]

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

FIG. 2 is a circuit block diagram of another embodiment of the present invention.

[Explanation of symbols]

 1 Built-in microphone 2 Trap circuit 3 Switch 5 Level detection circuit 6 Comparison circuit

Claims (1)

[Claims] 1. A built-in microphone, filter means for reducing a predetermined frequency band component of a first sound signal obtained from the built-in microphone and outputting as a second sound signal, and selecting one of the first and second sound signals. A selection unit that selects a single level, a level detection unit that detects the level of the first audio signal or the second audio signal, and a comparison between the level detection unit output and a predetermined level. When the level exceeds the predetermined level, the selection means selects the first audio signal, and when the level of the output of the selection means falls below the predetermined level, the selection means outputs a selection control signal for selecting the second audio signal. A micro controller comprising a selection control means, a cylinder around which a magnetic tape is wound, and a magnetic head for recording the output of the selection means on the magnetic tape is mounted. Down internal magnetic storage device.