JPS6046886B2 - Digital automatic level setting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital automatic level setting device suitable for use in tape decks, etc. In particular, the present invention is capable of automatically setting the optimum level without compressing the dynamic range of an input signal. It is something.

Conventionally, when trying to record on a tape deck, etc., the input signal was adjusted to an appropriate level with a manual variable resistor while ignoring the VU meter, or the input signal was adjusted to an appropriate level using a manual variable resistor.
The recording level was automatically adjusted according to the average value of the input signal using an automatic gain control device called .

However, the former method of adjustment is cumbersome to operate;
Furthermore, in the latter case, there is a problem that the dynamic range of the input signal is compressed and recorded, so the following methods have been proposed to overcome this problem.

The first method is to increase the amount of attenuation by driving a motor connected to a variable resistor when a large input signal arrives, thereby attempting to perform distortion-free recording. This not only increases the number of mechanical components, but also is not completely satisfactory in terms of accuracy. The second circuit consists of a circuit that generates a DC voltage according to the signal level, and a circuit that stores the DC voltage and controls the gain of the signal transmission path according to the stored signal. update the memory signal by the switch,
There is a method of setting the gain according to a large input signal.
In this case, a capacitor is usually used as the memory element, and even if a variable resistance element with high input resistance such as a field effect transistor is used, it is difficult to maintain the same gain for a long time due to leakage current of the capacitor. It was difficult.
Furthermore, even if an ideal memory element were available, there would be drawbacks such as limitations in control linearity and control range because analog quantities were handled. The present invention detects an input signal level;
By converting it into a digital quantity using an AD (analog-digital) converter and digitally controlling the amount of signal attenuation of a group of signal attenuators arranged in the signal transmission path, the level is set. The object of the present invention is to provide a digital automatic level setting device that can solve the above-mentioned conventional problems.

Hereinafter, the present invention will be explained based on illustrated embodiments. FIG. 1 is a block diagram showing the main circuit configuration of an embodiment of the present invention, in which 1 and 2 are signal input terminals and output terminals, respectively, and 3 is a resistance attenuator group, which is a group of signal attenuators. in groups,
This is arranged between the input terminal 1 and the output terminal 2.

Level detector 6 is connected to input terminal 1, and its output is A
It reaches the digital counter 5 via the D converter 7, the subtracter 32, the AND gate circuit 12, and then the latch circuit 14.
The signal is supplied to the resistance attenuator group 3 via the. In the configuration shown in FIG. 1, an analog signal such as an audio signal is applied to the input terminal 1, and an analog signal with a set level is obtained at the output terminal 2. In FIG. 1, the level detector 6 is, for example, a circuit that detects the peak level of an input signal.
It usually consists of an absolute value circuit and a smoothing circuit with a short time constant.

The reference level generator 4 provides reference information for level setting, and generates a digital value corresponding to the input level at which the variable attenuation circuit 3 starts attenuation. A subtracter 9 receives a digital value corresponding to the input signal level obtained by the level detector 6 and the AD converter 7 from the reference level generator 4. Outputs a digital value corresponding to the difference from the digital value of . That is, the subtracter 9 performs subtraction between the two digital values, and a digital value corresponding to the level at which the input signal exceeds the reference level appears at its output. This is AN
It is applied to the counting terminal (IN) of the digital J counter 5 via the D gate circuit 12. The pulse generator 10 generates a clock pulse for the oil converter 7 and a clear pulse for clearing the digital counter 5 every time the oil converter 7 samples. AND gate circuit 12, 1
3 and the inverter 11 function to control the digital counter 5 to a counting or holding state by operating the switch 8. The latch circuit 14 and the comparator 15 function to hold the maximum count value, and the latch circuit 14 outputs the count value of the digital counter 5 as it is in the non-latched state, and maintains the previous value regardless of the input in the latched state. do the work. The comparator 15 is connected to the counting outputs Al, A2, A3, A4 of the digital counter 5 and the output Bi of the latch circuit.
. 14. As is clear from the above explanation, the latch circuit 14 and the comparator 15
are the counting outputs Al, A2, A3, of the digital counter 5,
A! i is the previous latch output Bl, 8, B3, B, respectively
The latch/output is updated only when it is larger than 4, and the previous output is held when it is smaller.

Therefore, the maximum value of the count values sequentially sent from the digital counter 5 is obtained as the output of the latch circuit 14. The resistance attenuator group 3 is composed of four stages of resistance attenuators and analog switches.

Resistors 16 and 17, analog switch 18, and buffer amplifier 19 constitute a first-stage resistance attenuator, and output 2 of latch circuit 14 applied to the gate of analog switch 18 is "H"('rl'L logic). High level), conductive state, “L” (TTL logic low level)
Since it becomes a cutoff state when , the output of the latch circuit 14 ends up being ? When is “H”, the first stage resistor attenuator is resistor 16 and 1
It exhibits an attenuated state compared to the partial pressure ratio of 7, and ? When is "L", it is in a non-damped state. The buffer amplifier 19 serves to prevent mutual influence between the first and second stage resistive 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; 29, analog switch 30, and buffer amplifier 31 constitute a fourth stage resistance attenuator. Each of the resistance attenuators from the first stage to the fourth stage is connected in cascade to form the resistance attenuator group 3.
and each resistive attenuator has a different amount of attenuation in its attenuation state, for example, 1dB12c1B14dB. ．． 8c
[Set to B. When attempting to set the level in the digital automatic level setting device shown in FIG. 1, the switch 8 is pressed to bring it into the setting state.

The input signal is converted by the level detector 6 into a DC voltage corresponding to either a positive or negative peak level, which is sampled at regular intervals by the AD converter 7, and the sampled value is converted into, for example, the number of pulses. The subtracter 9 converts the digital value into a digital value corresponding to a level exceeding the reference value generated by the reference level generator 4, and sends it to the AND gate circuit 12 at regular intervals. Now, since the switch 8 is pressed and is in a short-circuited state, an "H" level is applied to the other input terminal of the AND gate circuit 12 via the inverter 11, and the output pulse of the subtracter 9 is sent to the digital counter 5. will be applied to the counting input terminal (IN).

“H” through the inverter 11 is applied to the AND gate circuit 13.
A level and a clear pulse are applied from the pulse generator 10, and the output thereof is given to the clear input of the digital counter 5. The clearing pulse from the pulse generator 10 is generated in synchronization with the pigeon converter 7 sampling at regular intervals, and immediately before the AD converter 7 converts the sampled value into a pulse number and outputs it. In short, the clear pulse applied to the clear input terminal (CL) of the digital counter 5 clears the count value of the digital counter 5 to O so as not to accumulate the previous count value, and the count value corresponding to the next sample value is cleared. be prepared. Therefore, the digital counter 5 outputs a count value corresponding to a sample value for each fixed period at which the input signal exceeds the reference level.
This count value is determined by the maximum value holding operation by the latch circuit 14 and comparator 15 described above, so that the maximum value during the period when the switch 8 is pressed is the output Bl, B2 of the latch circuit 14.
, B3, and B4. The output of the latch circuit 14 is for each analog switch 18, 22, 26, 3 of the resistance attenuator group 3.
0 and controls the first to fourth stage resistance attenuators to be attenuated or non-attenuated, thereby controlling the total attenuation amount of the resistance attenuator group 3. In this example, the peak level of the input signal is very high, and the outputs Bl, B2, and
When B3 and B4 are all set to "H", each resistor attenuator is all attenuated, and the attenuation amount is 15 dB, so that the signal applied to input terminal 1 is attenuated by 15 dB and sent to output terminal 2. In addition, if the peak level of the input signal is very low and does not meet the reference level, for example, when all the outputs of the latch circuit 14 become "L", the resistor attenuator group 3 becomes a non-attenuating state, and the input signal is not attenuated. It will be sent to output terminal 2. Therefore, a signal at a substantially constant level is obtained at the output terminal 2 with respect to an input signal exceeding the reference level. When switch 8 is released, AN
Since "L" level is given to the inputs of the D gate circuits 12 and 13, the counting manual terminal (I
No pulse is applied to the clear input (CL) and the counting and clearing operations are not performed. Therefore, the output of the latch circuit 14 continues to hold the previous count value. In this way, the switch 8 is in the setting state when it is short-circuited and is in the holding state when it is open. In the setting state, the peak value of the input signal is measured and a level setting corresponding to that peak value is executed, and in the holding state, the level Keep your settings. The digital automatic level setting device described in FIG. 1 can be used, for example, to set the recording level of a tape deck.

In this case, the output terminal 2 is connected to the recording amplifier of the tape deck, and a recording current is supplied to the Isoke head. In the setting state of the switch 8, the attenuation amount of the resistive attenuator group 3 is set so that, for example, the peak of the input signal is recorded at the maximum recording level of the magnetic tape. This can be easily set by adjusting the digital value generated by the reference level generator 4.
In this way, the peak 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 distortion-free recording can be automatically performed. The digital automatic level setting device of the present invention performs optimal level setting by simply pressing the switch 7, which frees you from the hassle of operation and also eliminates the worry that the dynamic range of the input signal will be compressed and recorded. do not have.

Furthermore, since it can be performed purely electronically without using mechanical parts such as a motor, it is easy to reduce costs. In addition, compared to conventional analog systems, since control is performed using digital signals, it is possible to achieve much higher precision, and the retention time in the retention state is permanent as long as the power is turned on. It has a number of excellent features, such as the fact that there is no need to worry about setting level drift due to leakage current. Furthermore, another great effect is that the signal generated by the reference level generator 4 is a combination of "H" and "L" (in the embodiment, 4
It has an extremely simple configuration because it only needs to be supplied with a combination of two (1) combination of two (2) combinations), and although it is step-like, it is convenient for level setting, and the device is highly reliable against temperature characteristics, power supply voltage fluctuations, various noises, etc. This is possible. FIG. 2 shows another embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals.

This embodiment is designed so that the reference level generator 4 generates a plurality of types of reference information, and by using it, several types of setting values for automatic level setting can be selected. The reference level generator 4 is configured to output three types of reference levels as digital values, for example L. ．． H,. A 4-bit digital value (equivalent to 7 in W base) along with HlH is used as the first reference information by the selector switch 3.
It is given to the a contact point of 2. Here, L is TTL(7)L
The H level can be obtained by connecting to the ground, and the H level can be obtained by connecting to Vcc (power supply voltage), which is the TTL H level, so the configuration is extremely simple. Similarly, HlL. ．． L. ．． The digital value of H (corresponding to 9 in W base) is sent to the b contact of the selector switch 32, and the H. L. H. H (corresponding to 11 in decimal notation) is applied to the c contact of the changeover switch 32, respectively. The digital values corresponding to the respective reference levels thus given are selected by the d contact (common contact) of the changeover switch 32 and added to the subtracter 9. Therefore, the D contact of the changeover switch 32 becomes the A contact! If the first reference level is selected by connecting to the point, the subtracter 9 is activated only when the input signal reaches a high level exceeding the first reference level.
When a digital value of 1 or more appears at the output of the resistor 5, the counter 5 is counted and one of the attenuators in the resistive attenuator group 3 is put into an attenuating state. Thereafter, if the second and third reference levels are selected, attenuation will start sequentially from the higher portions of the input signal.
In short, the selector switch 32 selects the control start point of the automatic level setting device, in other words, the level obtained at the output terminal 2 is selected. If a conventional attenuator using a variable resistor was used in the recording circuit of a tape deck, the user would set the level by operating the variable resistor while monitoring the VU meter. The indicated value changes from moment to moment, and it requires considerable skill to set it to the highest level.

On the other hand, if a digital automatic level setting device as shown in the above embodiment is used, there is no need to monitor the VU meter, and the user can simply press and release the switch 8 for a certain period of time, and the optimum level will be automatically set. This makes it extremely easy to make high-quality recordings. If you want to record with this device without any saturation distortion, it would be ideal to measure the source you are trying to record once in the setting state, then switch to the hold state and record. When recording music, the peak level can be detected not only by setting the switch 8 for several seconds to several tens of seconds.

As described in detail above, the present invention detects the input signal level, converts it into a digital value using an oil converter, calculates the difference between the input signal level and the digital value indicating the reference level, calculates the maximum value of the result, and calculates the maximum value of the result. Since the level is set by digitally controlling the amount of signal attenuation of a group of signal attenuators placed in the signal transmission path, it is possible to set the level in the recording circuit of a tape deck. This provides an excellent effect in that high-quality recording without saturation distortion can be performed automatically.

Furthermore, the present invention has the excellent feature that the gain is set digitally, so it is highly accurate and there is no drift in the set gain.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a main part of one embodiment of the present invention, and FIG. 2 is a diagram of a circuit diagram of a main part of another embodiment of the invention. 1...Input terminal, 2...Output terminal, 3
... Resistance attenuator group, 4 ... Reference level generator, 5 ... Digital counter, 6 ...
Zeta detector, 7...Oil converter, 8...
...Switch, 9...Subtractor, 10...
・Pulse generator, 14...Latch circuit, 15...
Comparator, 32...changeover switch.

Claims (1)

[Claims] 1. A group of signal attenuators disposed on an analog signal transmission path;
a level detector that detects the input signal level of the analog signal transmission path; an AD converter that converts the output of the level detector into a digital signal; a reference level generator that generates a digital signal corresponding to a reference level; A subtracter that obtains the difference signal between the output of the AD converter and the output of the reference level generator, a digital counter to which the digital output of the subtracter is input and that performs counting according to the digital input, and a maximum count of the digital counter. a latch circuit and a comparator that hold a value and control the amount of signal attenuation of the signal attenuator group, and attenuate the signal of the signal attenuator group in accordance with the level at which the input signal of the analog signal transmission path exceeds a reference level. A digital automatic level setting device characterized in that it is configured to control the amount. 2. In the statement of claim 1, the reference level generator is configured to generate a plurality of types of reference levels, and to select and use one of the reference levels by switching a switch. Digital automatic level setting device.