JPS5935871Y2 - Recording level adjustment device using bar graph meter - Google Patents

Description

[Detailed description of the invention] This invention is a level adjustment method using a bar graph meter to match the signal input level during recording and the output level during playback of a test signal in a device that performs magnetic recording and playback such as a tape recorder. It is related to the device.

In a magnetic recording/playback device such as a tape recorder, it is desirable that the recording input level and the playback output level match. Particularly in tape recorders equipped with the Dolby noise reduction system or dBX system, the recording signal It is essential for optimal recording and playback that the input level and the playback output level match.

For this reason, level meters have traditionally been used to match the recording input level and the playback output level, but it is necessary to judge whether the two levels match based on the degree of deflection of the pointer. Therefore, it had the disadvantage that level adjustment was extremely difficult.

The present invention displays the level using a bar graph meter, making it extremely easy to judge whether the recording level and the playback output level match.
The test signal is subjected to AM modulation with an amount of change smaller than that between the predetermined elements of the bar graph meter, thereby making it possible to perform accurate level adjustment.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a test signal generating circuit which generates a high frequency signal of constant amplitude as shown in a.

2 is a rectangular wave generation circuit such as a flip-flop (
AM modulation circuit) generates a rectangular wave as shown in b, turning transistor 3 on and off.

By turning on and off the transistor 3, the waveform of the test signal at point B is AM modulated and becomes as shown in Fig. 2.
The amount of change in this test signal, that is, the level difference C, is determined by the resistance 4
This can be determined by adjusting the variable resistor 5 connected in series with the variable resistor 5.

In this embodiment, the variable resistor 5 is adjusted to reduce the level difference C.
, 2ctB.

Switch S is a level adjustment switch, and is switched to the terminal 6 side for normal recording and playback, and to the terminal T side for level adjustment.

8 is an amplifier, 9 is a resistor for adjusting the recording level, and the test signal is recorded on the tape T by the recording head 11 through the recording amplifier 10.

The test signal recorded by the recording head 11 is taken out as a reproduction output by the reproduction head 12.

The retrieved reproduction output is amplified by a reproduction amplifier 13, and then taken out by a line 15 in order to display its level by a bar graph meter 14, and passed through a rectifying and smoothing circuit 16 and a display driver 17 to a bar graph meter 14. The level of the reproduction output is displayed on the R channel of the graph meter 14.

In addition, the test signal amplified by the amplifier 8 is taken out as a monitor output as a line 18 in order to display the input level of the test signal by a bar graph meter 14, and is outputted from a rectifying and smoothing circuit 19 as well as a display.・
The input level of the test signal is displayed on the L channel of the bar graph meter 14 through the driver 20.

Therefore, when the AM-modulated test signal shown in FIG. 2 passes through the rectifying and smoothing circuit 19, it becomes as shown in FIG. 3, and this level is applied to the L channel of the bar graph meter 14.

The input level of these test signals and the level of their reproduced output are as shown in Fig. 4) Display element 2 of the bar graph meter.
1, but the level of the test signal is the level difference C
In this example, it is set to 0.2 dB, so the level of the test signal is adjusted so that +3 dB blinks on the L channel indicating the input level of the test signal, There is also an R channel that displays the playback output level.
By adjusting the recording level adjusting resistor 9 so that the signal blinks by 3 dB, the level of the test signal and the level of the playback output can be matched within an error range of 0.2 ctH.

In the above embodiment, a rectangular wave is used as a means for AM modulation, but instead of a rectangular wave, a sine wave or a triangular wave may be used.

As a circuit for generating a rectangular wave, if a tape recorder is used, the structure can be simplified by using an on/off signal for a shut-off circuit generated by the rotation of a reel stand.

Further, even if the tape recorder has a normal recording/reproducing head without a recording head and a reproducing head, the level can be adjusted in the same way by rewinding and reproducing the tape after recording.

As is clear from the above, in the present invention, the level difference between the predetermined elements of the bar graph meter (
In this example, the amount of change (2 dB difference between +1 dB and +3 dB, or 2 dB difference between +3 dB and +5 dB) is smaller.
An element (explained as 0.2 dB in this example) that applies AM modulation and displays both the peak values of the input level of the test signal and the playback output level of the recorded and played back test signal. Since the input level of the test signal and the playback output level are matched by making the element that displays +3 dB blink, the error in level matching can be kept small regardless of the level difference between the display elements. Since it is possible to suppress the error to less than the amount of change multiplied by AM modulation, accurate level adjustment can be performed.

[Brief explanation of drawings]

The figures show one embodiment of the present invention. Fig. 1 is a circuit diagram of the invention, Fig. 2 is a waveform diagram at point B in Fig. 1, and Fig. 3 is a waveform diagram when adding to bar graph make. FIG. 4 is an explanatory diagram showing display elements of the bar graph meter. 1...Test signal generation circuit, 2...Square wave generation circuit, 3...Transistor, 9...
- Recording level adjustment resistor, 11... recording head, 12... playback head, 14... bar graph meter.

Claims (1)

[Scope of utility model registration request] A test signal generation circuit that generates a test signal at a constant level, a bar graph meter that displays the input level of the test signal and a playback output level of the test signal recorded and played back, and a bar graph meter that displays the test signal. and an AM modulation circuit that applies AM modulation with an amount of change smaller than the level difference between the predetermined elements of the bar graph meter, and applies AM modulation with an amount of change smaller than the level difference between the predetermined elements of the bar graph meter to the test signal. The human power level of the test signal and the reproduction output level are displayed by a bar graph meter, and an element of the bar graph meter that displays the peak value of both the levels is blinked, and an element that displays a level below that level is lit. A recording level adjustment device using a bar graph meter, characterized in that the level is adjusted by using a bar graph meter.