JPS6118826B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic recording level setting device suitable for use in tape decks, etc., and in particular, it automatically sets the recording level when the power is turned on, so that recording can be performed at the optimal recording level even when recording while you are away. It was designed so that

Recently, it has been proposed to automatically set the recording level in tape decks and the like. This is a one-touch switch that automatically sets the gain according to the maximum level of the input signal over a suitable period, compared to the conventional method of manually adjusting the recording level while monitoring a VU meter. The feature is that it is very easy to set the optimum recording level.

The present invention is an automatic recording level setting device of this kind, in which the optimum recording level can be set even when recording while the user is away, and one embodiment thereof will be described below with reference to the drawings.

First, Figure 1 is a circuit block diagram of the main part of the automatic recording level setting device, where 1 and 2 are signal input and output terminals, respectively, and 3 is a gain control circuit that changes the gain between input terminal 1 and output terminal 2. It is.

4 is a level detector which functions to detect the level of the signal applied to the input terminal 1; Reference numeral 5 denotes a maximum value holding circuit, which functions to hold the maximum value of the levels detected by the level detector 4 and supply a corresponding control signal to the gain control circuit 3. 6
is a time setting circuit which generates a pulse of a constant time width by operating an automatic setting switch 7 and supplies it to the maximum value holding circuit 5.

In the above configuration, when the operator presses the automatic setting switch 7, the time setting circuit 6 is immediately driven.
A pulse with a time width corresponding to a predetermined set time is generated, and this pulse is applied to the maximum value holding circuit 5. The maximum value holding circuit 5 holds the maximum level detected by the level detector 4 within the time set by the time setting circuit 6, and supplies a corresponding control signal to the gain control circuit 3. Therefore, the gain control circuit 3 is controlled to a gain determined by the maximum level of the input signal within a certain period of time.

Here, assuming that the output terminal 2 is connected to the recording amplifier of the tape deck and a recording current is supplied to the magnetic head, the maximum retention time measured during the time determined by the time setting circuit 6 is calculated. The voltage is set to control the gain control circuit 3 so that the peak of the input signal is recorded, for example at the maximum recording level of the tape.

In this way, the maximum level of the input signal is recorded at the maximum recording level of the magnetic tape, and other signal levels are recorded below the maximum recording level. Therefore, the input signal is recorded without being subjected to saturation distortion of the magnetic tape, and without compressing the dynamic range of the input signal. The recording level can be set by simply pressing the automatic setting switch 7, which is an extremely easy operation compared to the conventional recording level setting.

Here, it is sufficient to set the automatic recording level by one-touch operation for about 10 seconds.

FIG. 2 shows a more specific embodiment of the main parts of the present invention, and the same parts as in FIG. 1 are given the same reference numerals. In FIG. 2, the recording level can be set by simply pressing the automatic setting switch 7. When automatic setting switch 7 is shorted, monostable multivibrator 32
is driven, one pulse with a time width corresponding to the maximum value measurement time explained in Fig. 1 is generated, and the AND
added to gate circuits 12 and 13. The input signal applied to the input terminal 1 is converted by the peak detector 9 into a DC voltage according to the peak level of the signal, and this is converted by the analog-to-digital (AD) converter 11 into a number of pulses, which is a digital signal. Ru.

During the measurement period, that is, the period when the monostable multivibrator 32 is generating pulses, AND
A pulse is applied to the digital counter 8 via the gate circuit 12 and the AND gate circuit 13 to perform counting. Digital counter 8, latch circuit 1
4. The comparator 15 constitutes the maximum value holding circuit 5 shown in FIG. 1, and has the function of detecting and holding the maximum value among the number of pulses corresponding to the input level successively sent from the AD converter 11. do.
In other words, the maximum value holding operation is performed digitally,
The digital output is given to the gain control circuit 3 as a control signal. The gain control circuit 3 includes a plurality of resistor attenuators including analog switches, and each resistor attenuator is controlled to be attenuated or not attenuated according to the digital output given from the latch circuit 14, and the total amount of attenuation is determined. be done. Therefore, the attenuation amount is set in accordance with the maximum input during the maximum value measurement period during which the monostable multivibrator 32 is generating pulses. That is, when the maximum input is large, the attenuation amount is set to be large. When the measurement period ends and the pulse generation operation of the monostable multivibrator 32 stops, the pulses from the AD converter 11 are blocked by the AND gate circuit 12, and the pulses from the pulse generator 10 are blocked by the AND gate circuit 13, and the pulses are blocked by the digital counter. 8, the digital counter 8 does not perform any counting and continues to hold the count value counted during the measurement period. Therefore, the attenuation amount of the gain control circuit 3 is also maintained at a value corresponding to the maximum input level set during the measurement period.

The peak detector 9 is a circuit that detects the peak level of an input signal, and is usually composed of an absolute value circuit and a smoothing circuit with a short time constant. The pulse generator 10 is
A clock pulse for the AD converter 11 and a clear pulse for clearing the digital counter 8 every time the AD converter 11 samples are generated. This clear pulse is synchronized with the AD converter 11 sampling every fixed period, and
It is generated immediately before the converter 11 converts the sample value into a pulse number and outputs it. In short, the clear pulse applied to the clear input terminal (CL) of the digital counter 8 clears the count value of the digital counter 8 to 0 so as not to accumulate the previous count value, and returns the count value corresponding to the next sample value. Prepare. Therefore, the digital counter 8 outputs a count value corresponding to a sample value of the peak level of the input signal every fixed period.

The AND gate circuits 12 and 13 function to control the digital counter 8 to a counting or holding state depending on the presence or absence of a pulse from the monostable multivibrator 32. The digital counter 8, the latch circuit 14, and the comparator 15 form the maximum value holding circuit 5 in FIG. It functions to maintain the previous value. The comparator 15 compares the counting outputs A ₁ , A ₂ , A ₃ , A ₄ of the digital counter 8 with the outputs B ₁ , B ₂ , B ₃ , B ₄ of the latch circuit,
Outputs a pulse only when there is a relationship of A>B,
This pulse unlatches the latch circuit 14, rendering it unlatched, and outputs the output of the digital counter 8 to the latch circuit 14.

As is clear from the above explanation, latch circuit 1
4 and a comparator 15 update the latch output only when the count outputs A ₁ , A ₂ , A ₃ , A ₄ of the digital counter 8 are respectively larger than the previous latch outputs B ₁ , B ₂ , B ₃ , B ₄ , When it is small, the previous output is retained.
Therefore, the maximum value of the count values sequentially sent from the digital counter 8 is obtained as the output of the latch circuit 14.

The gain control circuit 3 is composed of a four-stage resistive attenuator and an analog switch. Resistors 16 and 17, analog switch 18, and buffer amplifier 19 constitute a first-stage resistance attenuator, and analog switch 18 receives the output B ₁ of latch circuit 14 "H" (high level of TTL logic) applied to its gate. When the output _B1 of the latch circuit 14 is "H", the first stage resistor attenuator is connected to the resistor 16. It exhibits a damped state with a partial pressure ratio of 17, and becomes a non-damped state when _B1 is "L". The buffer amplifier 19 serves to prevent mutual influence between the first and second stage resistor attenuators. Similarly, resistors 20, 21, analog switch 22, and buffer amplifier 23 form a second stage resistance attenuator, resistors 24, 25, analog switch 26, and buffer amplifier 27 form a third stage resistance attenuator, and resistor 28, 29, analog switch 30, and buffer amplifier 31 constitute a fourth stage resistance attenuator. The resistive attenuators from the first stage to the fourth stage are connected in cascade to form a gain control circuit 3, and each resistive attenuator has a different attenuation amount in the attenuation state, for example, 1 dB, 2 dB, 4 dB, 8 dB, etc.
It is set to dB.

As mentioned above, in this circuit, automatic setting switch 7
You can digitally set the optimal recording level with just one touch. Since the set level continues to be held at a constant value after the setting is completed, the set level does not change during recording, and high-quality recording can be performed.

The present invention is such that such an automatic recording level setting circuit operates even when the power is turned on.
As shown in the figure, the output terminal 2 of the automatic recording level setting circuit A shown in FIGS. 1 and 2 is connected to the recording amplifier 33.
The DC voltage obtained from the tape deck power supply circuit 35, which supplies power to the automatic recording level setting circuit A, the recording amplifier 33, etc., is also supplied to the differentiating circuit 36. ing.

The output of the differentiation circuit 36 is applied to a switching element 38 such as a transistor connected in parallel to the automatic setting switch 7 of the automatic recording level setting circuit A via a selection switch 37.

As a result, with the selection switch 37 currently closed, the power switch 39 to the power supply circuit 35 is closed,
When the power supply circuit 35 operates, one pulse is generated at the output of the differentiating circuit 36, and this pulse causes the switching element 38 to become conductive for a moment.
Automatic recording level setting circuit A operates in the same manner as when automatic setting switch 7 is operated.
The recording level is automatically set.

Therefore, if the power switch 39 is used as a timer switch for recording when the user is not at home, recording will be performed at the optimum recording level even during this recording when the user is not at home. It should be noted that the selection switch 37 can be used to select whether or not to automatically set the recording level when the power is turned on.

As described above, the present invention detects the input signal level with a level detector for a predetermined period of time in a time setting circuit activated by the operation of an automatic setting switch, and detects the input signal level within the certain period of time. The automatic recording level setting circuit is configured to operate the gain control circuit and automatically set the output signal level according to the maximum level of the signal, so the level can be detected within a certain period of time determined by the time setting circuit. The maximum level can be detected based on the current setting, the operability of the automatic setting switch can be significantly improved, and the previous setting state can be reset and the level setting can be newly updated by operating the automatic setting switch. Moreover, since a switch means that operates only when the power is turned on is connected in parallel to the automatic setting switch that constitutes the automatic recording level setting circuit, when the power is turned on, a predetermined constant level is set by the time setting circuit that is activated by this switch means. The recording level can be automatically set to the optimum value within the specified time, and good recording can be made even when the user is away from home.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an automatic recording level setting circuit according to the present invention, FIG. 2 is a detailed diagram of the same circuit, and FIG. 3 is a block diagram of an embodiment of the present invention. A... Automatic recording level setting circuit, 3... Gain control circuit, 4... Level detector, 7... Automatic setting switch, 35... Power supply circuit, 37... Selection switch, 38... Switching element, 39... ...Power switch.

Claims (1)

[Claims] 1. The input signal level is detected by a level detector for a predetermined period of time in a time setting circuit activated by the operation of an automatic setting switch, and the maximum input signal level within that period of time is detected. An automatic recording level setting circuit configured to automatically set the output signal level by operating a gain control circuit according to the level is connected in parallel to an automatic setting switch that constitutes the automatic recording level setting circuit. An automatic recording level setting device characterized in that it is equipped with a switch means that operates only at certain times. 2. The automatic recording level setting device according to claim 1, further comprising a selection switch for selecting the operation of the automatic recording level setting circuit by the switch means.