JPH0546397Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a recording circuit for equipment having a built-in microphone, such as a video camera or a tape recorder.

(b) Conventional technology Generally, video cameras, tape recorders, etc. have a built-in microphone for recording surrounding sounds. The built-in microphone records sounds related to
02) Reference). In the case of such video cameras and tape recorders, it is necessary to properly record a wide range of sound levels from short distances to long distances, so an automatic gain control circuit (ALC) is installed in the recording circuit.
circuit) to prevent distortion from occurring during large inputs.

(c) Problems that the invention aims to solve However, for example, when recording is performed with such a video camera, the person who is the subject of the recording and recording must be several meters to several tens of meters away from the video camera. Therefore, the recording level of the sound to be recorded is very low compared to the recording level of the sound generated near the video camera.
In addition, a large amount of noise such as coughing, conversation, and operation sounds made by the photographer is recorded, resulting in a problem in that many unnecessary sounds are included during playback. Furthermore, if various noises like those mentioned above occur near the video camera, the ALC circuit will suppress the recording sensitivity, causing the inconvenience that the desired sound will not be recorded at all for several seconds. was.

(d) Means for solving the problems In order to solve the above problems, the present invention has two
a stereo/monaural switch for switching between stereo and monaural use of each built-in microphone; and a stereo/monaural switch for switching between stereo and monaural use of each built-in microphone; The left and right recording amplifiers are inputted with separate signals, and when the stereo/monaural switch is set to the monaural position, the built-in microphones are switched to the far or near position so that the built-in microphones can be input in the same phase or in opposite directions. It consists of a change-over switch that connects the mixed microphone signals in series in phase and inputs the mixed microphone signals to each of the recording amplifiers respectively.When recording monaural sound from a short distance, the change-over switch is switched to the short-distance position to input the mixed microphone signal to the long-distance sound with the same phase. The sound is attenuated, and when recording distant sounds in monaural, the changeover switch is switched to the far position to attenuate near-field sounds having an opposite phase.

(E) Effect In the recording circuit of the present invention having the above configuration, when the sound source to be recorded is far away, the same phase sound is input to the two built-in microphones, and when the sound source is nearby, the sound is input to the two built-in microphones. The polarity of the two built-in microphones can be switched to in-phase or anti-phase by taking advantage of the fact that opposite-phase sounds are input to the input terminal, so that only the desired short-range sound can be recorded when monaurally recording short-range sounds. It is also possible to extract and record only the target distant sound when making monaural recordings of distant sounds.

(F) Embodiment An embodiment of the present invention will be described below with reference to the drawings.

In other words, 1 and 2 in the figure are two built-in microphones, and they can be installed on different sides of the device, or even on the same side, separated from each other or with a partition wall in order to pick up near-field sounds at different phases. It is being 3, 4, 5, and 6 are stereo/monaural changeover switches for switching between stereo use and monaural use of each of the built-in microphones 1 and 2, and 7 and 8 are stereo/monaural changeover switches 3, 4, and 5 for switching to the stereo position. When the built-in microphones 1 and 2 are installed, the microphone signals from the built-in microphones 1 and 2 are input separately into left and right recording amplifiers, and 9 to 13 are used for monaural recording of near-field sounds and monaural recording of far-field sounds. A changeover switch that can be switched between a short distance position (LOCAL) and a long distance position (DX), and the changeover switches 9, 10, and 11 switch the built-in microphones 1 and 2 in opposite phases at the short distance position (LOCAL). The built-in microphones 1 and 2 are connected in series in the same phase at their distant positions (DX), and their mixed microphone signals are input to the respective recording amplifiers 7 and 8, respectively. There is. 14 and 15 are the respective recording amplifiers 7 and 8.
The ALC circuit operates level adjusters 16 and 17 provided at the input ends of each of the recording amplifiers 7 and 8 to adjust the microphone signal level. 18, 19 and 20, 21 are time constant capacitors that determine the recovery time of each of the ALC circuits 14, 15, respectively, and their capacitance values are as follows: time constant capacitors 18, 20≫time constant capacitors 19, 21. The switching circuits 12 and 13 selectively connect to the ALC circuits 14 and 15, respectively. Reference numeral 22 denotes a focus voltage generation circuit linked to the focusing mechanism, and its output voltage Ve increases as the focus is varied from near to long distance. Specifically, in the case of an automatic focusing type, it is linked to a lens drive mechanism, etc., and in the case of a manual focusing type, it is linked to a focus ring. A comparison circuit 23 compares the output voltage Ve from the focal voltage generation circuit 22 with a reference voltage Vref set by resistors 24 and 25, and when Ve>Vref, its output is inverted to H level. Reference numeral 26 denotes a driving transistor that turns on when the output of the comparator circuit 23 becomes H level, and 27 denotes the driving transistor 2.
6 is a relay that is energized to switch each of the changeover switches 9 to 13 to a long distance position (DX).

Therefore, according to the recording circuit of the present invention, when recording a person at a close distance with a video camera,
When Vref>Ve, the output of the comparison circuit 23 becomes L.
Level - OFF state of drive transistor 26 - Relay 27 is in a non-energized state, and each of the changeover switches 9 to 13 is switched to a short distance position (LOCAL). Therefore, the built-in microphones 1 and 2 are connected in series with opposite phases by the changeover switches 9, 10, and 11, and distant sounds input in the same phase are attenuated on the microphone output side. The signal is not input to the recording amplifiers 7 and 8. Therefore, short-distance sounds input with opposite phases are input to the recording amplifiers 7 and 8 through the resistors 28 and 29, respectively, without being attenuated on the microphone output side.

Next, when recording a distant person with a video camera, Ve>Vref and the output of the comparison circuit 23 is at H level - the driving transistor 25 is in the ON state - the relay 29 is in the energized state. Then, each of the changeover switches 9 to 13 is switched to a long distance position (DX). Therefore, each of the built-in microphones 1 and 2 is connected to each of the changeover switches 9 and 2.
10 and 11 are connected in series with the same phase, and close-range sounds input with opposite phases are attenuated on the built-in microphone output side and are not input to the recording amplifiers 7 and 8. Therefore, distant sounds that are input in the same phase have twice the voltage on the microphone output side and are input to the recording amplifiers 7 and 8, respectively. Furthermore,
During monaural recording of such distant sound, the ALC circuits 14 and 1 are switched by the respective changeover switches 12 and 13.
Since the time constant capacitors 19 and 21 are connected to the terminals 5 and 5, the recovery time is shorter than that when monaural recording of nearby sounds, and the target distant sound can be heard for a long time after a sudden excessive input that occurs at a short distance. It is designed to prevent people from being masked.

(G) Effects of the invention As mentioned above, according to the recording circuit of the invention, by connecting two built-in microphones in series with the same phase or opposite phase, it is possible to attenuate distant sounds when recording short-distance sounds in monaural. Also, when recording distant sounds in monaural, it is possible to attenuate near-field sounds, and
The recovery time of the ALC circuit can be changed to a value suitable for monaural recording of short-range sounds and long-distance sounds.

[Brief explanation of the drawing]

The illustrated circuit is one embodiment of the recording circuit of the present invention. 1, 2...Built-in microphone, 3, 4, 5, 6
...Stereo/monaural selector switch, 7, 8...
...Recording amplifier, 9, 10, 11, 12, 13...
Changeover switch.

Claims (1)

[Scope of utility model registration request] There are two built-in microphones, a stereo/monaural changeover switch that switches between stereo use and monaural use of each built-in microphone, and when the stereo/monaural changeover switch is set to the stereo position, The left and right recording amplifiers input microphone signals separately, and when the stereo/monaural switching switch is switched to the monaural position, the built-in microphones are switched to the far or near position and are switched to the same phase or the same phase. It consists of a changeover switch that connects the microphone signals in series with opposite phases and inputs the mixed microphone signals to each of the recording amplifiers respectively.When recording close-range sound in monaural, the changeover switch is switched to the short-range position to input the mixed microphone signal to the same phase far-field sound. A recording circuit characterized in that a distance sound is attenuated, and when a long distance sound is monaurally recorded, the changeover switch is switched to a long distance position to attenuate a short distance sound having an opposite phase.