JPH0510254Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a so-called voice operation tape recorder that runs a tape to record only when there is a voice input.

BACKGROUND ART AND THEIR PROBLEMS FIG. 1 shows an example of a circuit of a conventional voice operation tape recorder.

In the figure, an audio signal obtained from a microphone 1 is amplified by a microphone amplifier 2, and then its level is detected by a level detection circuit 3. The level V ₁ of the detected audio signal is determined by the comparator 4 as the reference level V _S
When V ₁ ≧V _S , the output of the comparator 4 becomes “L” (low level). As a result, the transistor _Q1 is turned off, the drive circuit 5 including the servo circuit is operated, the motor 6 is rotated, and the tape 13 is run.

On the other hand, the output audio signal of the microphone amplifier 2 is applied to a delay circuit constituted by a BBD 8 through an amplifier 7, and is delayed for a predetermined time. This delay prevents the audio signal from being applied to the recording head 12 during the start-up time of the motor 6, thereby preventing the beginning of the audio from being cut off. After a clock component is removed from the delayed audio signal by a low-pass filter 9, it is applied to a recording head 12 through a recording amplifier 10 and an equalizer circuit 11, and is recorded on a tape 13.

When the audio signal from microphone 1 disappears
Since V ₁ <V _S , the comparator 4 is inverted and its output becomes "H" (high level). Therefore, the transistor _Q1 is turned on, the operation of the drive circuit 5 is stopped, and the power to the motor 6 is turned off.

The BBD 8 used in such a voice operation tape recorder is provided to prevent the recorded audio from being cut off at the beginning, as described above. However, this BBD8 is generally the second
It has input level vs. distortion rate characteristics as shown in the figure. That is, when the input level is -10 dBs or more, the distortion increases, and when the input level is low, the distortion rate worsens due to clock pulse leakage. For this reason, the range that can actually be used with good sound quality is a narrow range of about 10 dB. Moreover, the S/N ratio is poor and it is not practical except at limited input levels.

Purpose of the invention The purpose of the invention is to solve the above-mentioned problems in this type of voice operation tape recorder using BBD, and to enable recording and playback with always good sound quality.

Summary of the invention This invention applies AGC (automatic gain control) to the audio signal to maintain the input level of the BBD within an appropriate range.

Embodiment FIG. 3 shows an embodiment of the present invention, in which the same parts as in FIG. 1 are given the same reference numerals.

In FIG. 3, a portion of the output of amplifier 7 is applied to the base of transistor Q ₂ forming amplifier 14. In FIG. This amplified output is rectified and smoothed by diodes D ₁ and D ₂ and capacitor C ₁ to detect the level of the input audio signal. This detected level is applied as an AGC voltage to the base of a gain control transistor _Q3 connected to the input terminal of the amplifier 7, thereby controlling the gain of the audio signal. As a result, the output of the amplifier 7, ie, the input of the BBD 8, is maintained within an appropriate level range as shown in FIG. 4, for example.

By setting the gain distribution for amplifiers 2, 7, and 14 to, for example, 18 dB, 37 dB, and 9 dB, the BBD input will change from -12 to -30 dBs when the input audio signal changes from -72 to -30 dBs as shown in Figure 4. This is narrowed down to a change of -22dBs, which falls within the appropriate range shown in Figure 2.

In this way, in the present invention, the output of amplifier 7 is further added to amplifier 14, and its output level is detected.
Since the AGC voltage is obtained, AGC can be applied so that the input of BBD8 is within the appropriate range. In addition, the AGC attack time and recovery time are shortened to speed up response, and after a voice is interrupted, appropriate AGC can be applied to the next voice. In FIG. 3, the attack time is determined by the output impedance of the transistor _Q2 and the capacitor _C1 , and the output impedance is set low to make the attack time several milliseconds. Further, the recovery time is set to about 0.5 to 1 sec by the capacitor _C1 and the resistor _R1 .

Effects of the invention The input of the BBD of a voice operation tape recorder using a BBD to prevent cut-offs can always be kept within the appropriate range, thereby improving the distortion rate and S/N, resulting in good sound quality. Recording and playback can be performed.

[Brief explanation of the drawing]

Fig. 1 is a circuit block diagram of a conventional voice operation tape recorder, Fig. 2 is a BBD input level versus distortion characteristic diagram, Fig. 3 is a circuit diagram showing an embodiment of the present invention, and Fig. 4 is a circuit diagram of the present invention. FIG. 3 is a diagram of input versus BBD input characteristics of a tape recorder. In addition, in the symbols used in the drawings, 1...microphone, 4...comparator, 6...motor, 14...amplifier, _D1 , _D2 ...diode,
C ₁ ... Capacitor, Q ₃ ... AGC transistor,
It is.

Claims (1)

[Claims for Utility Model Registration] Audio-driven tape that is configured to run the tape and record when an audio signal is input, and which is provided with a BBD delay circuit in the signal supply path to the recording head. In the recorder, an amplifier circuit is connected to the input side of the BBD and amplifies the input signal of the BBD; a level detection circuit detects the output level of this amplifier circuit;
1. A sound-driven tape recorder comprising: a control circuit for controlling an input level of a BBD, and the input level of the BBD is set within a predetermined range.