JPH0445882B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic recording level setting device for a tape recorder that is capable of automatically setting an optimum recording level depending on the magnetic tape used.

Conventionally, the recording level in a tape recorder has generally been set by manually operating a recording level adjuster (recording volume) while observing the indication on a recording level meter. However, it is surprisingly difficult to set the recording level manually in this way, and with this method, the recording level may be insufficient and hysteresis noise of the magnetic tape becomes noticeable during playback, or There was a high possibility that recording errors would occur, such as the recording level becoming excessive and distortion becoming large.

As a solution to this problem, a recording level setting device using an automatic level adjustment circuit (hereinafter referred to as an ALC circuit) is known. For example, in the ALC circuit shown in Figure 1, the recording signal supplied to input terminal 1 is connected to resistor 2 and NPN transistor 3.
After passing through the variable attenuation circuit 4 having This detection output is used to control the collector-emitter resistance of the transistor 3, thereby making the signal level of the recording signal obtained at the output terminal 6 constant.

However, when such an ALC circuit is used, the dynamic range is narrowed due to the limiter effect of the ALC circuit, or a large amount of distortion occurs because the transistor 3 used in the variable attenuation circuit 4 is a nonlinear element. I had the problem of being exposed. Therefore, such an ALC
Recording level setting devices using circuits could only be used with simple tape recorders.

On the other hand, there are four types of magnetic tapes that have been commercially available in recent years: normal, chrome-based, ferrichrome, and metal. It is known that the maximum output level of the reproduced signal is such that the third harmonic distortion is 3% or less when recording is performed using a bias current.
Therefore, when setting the recording level, it is desirable to change the recording level depending on the magnetic tape used. For example, FIG. 2 is a diagram showing the operation and display section of an example of a conventional recording level setting device that takes into consideration that MOL differs depending on the type of tape. In this recording level setting device, VU
- On the peak meter scale 11 of the peak meter 10 (bar graph meter using light emitting diodes), there are zone markers 12 to 14 (corresponding to normal, chrome tape, ferrite, chrome tape, and metal tape, respectively) corresponding to the tape type. It is provided. When setting the recording level, target the zone marker corresponding to the type of tape in use on the peak meter scale 11, and set the recording volume 1.
5 (sliding recording volume). FIG. 3 is a diagram showing the operation and display section of another example of the conventional recording level setting device of this type. The name of the tape type is also written on each peak indicator 17 to 19, and when setting the recording level,
The recording level is adjusted so that the peak indicator corresponding to the tape type lights up from time to time. However, with the above-mentioned recording level setting device, the recording level that can be set is approximate, and even if the tape type belongs to the same family, magnetic tapes may differ if they are made by different manufacturers or from different production lots. Naturally, the recording level varies, so it is impossible to set an accurate optimal recording level.

This invention was made in view of the above-mentioned circumstances, and its purpose is to provide a tape recorder that can automatically set the optimum recording level according to the magnetic tape used without human intervention. An object of the present invention is to provide an automatic recording level setting device. In order to achieve this object, the automatic recording level setting device for a tape recorder according to the present invention includes (a) a test signal generation circuit that generates a test signal to be recorded on the magnetic tape used;
(b) The tape sensitivity is determined by comparing the test signal generated by the test signal generation circuit with the playback output signal of the recorded test signal, and the input is recorded on the magnetic tape according to this tape sensitivity. a first recording level setting circuit that sets a first signal gain of the signal; (c) a bandpass filter that extracts the playback output signal and high-frequency distortion components; and (c) a band-pass filter that extracts the reproduced output signal and high-frequency distortion components, and converts the extracted high-frequency distortion components into a DC voltage. a level detector; a reference voltage generator that generates a predetermined reference DC voltage; a comparison unit that compares the level of the DC voltage with the level of the reference DC voltage and outputs a comparison result; a recording level adjuster that amplifies or attenuates the input signal and supplies the amplified or attenuated signal to the first recording level setting circuit, and increases the second signal gain when the reference DC voltage becomes large as a result of comparison between the comparison means and the first recording level setting circuit; On the other hand, the present invention is characterized by comprising a second recording level setting circuit comprising a level control means that reduces the second signal gain when the DC voltage becomes large.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 4 is a block diagram showing the configuration of an embodiment of the present invention applied to a three-head tape recorder. Note that the erase head is omitted in this figure. The automatic recording level setting device for a tape recorder shown in FIG. 4 amplifies a recording signal supplied to a recording input terminal 20 by a recording circuit 21, supplies it to a recording head 22, and records it on a magnetic tape 23. Furthermore, in a tape recorder in which the signal reproduced by the reproduction head 21 is amplified through the reproduction circuit 25 and then outputted from the reproduction output terminal 26, the output of the test signal generation circuit 27 is sent to the recording circuit 24 and the recording head 22. so that it can be recorded on the magnetic tape 23 through the
Further, the MOL of the magnetic tape 23 is detected by the MOL detection circuit 28 using the reproduction signal of the test signal obtained from the output of the reproduction circuit 25,
Furthermore, using the output of this MOL detection circuit 28, a central processing unit such as a microprocessor (hereinafter referred to as
a level control unit 30 in 29 (referred to as CPU);
Recording level adjuster 31 in the recording circuit 21
The optimum recording level corresponding to the MOL of the magnetic tape 23 is automatically set by a recording level setting circuit 32 consisting of the following.

The configuration of each part of this embodiment will be explained in more detail below.The recording input terminal 20 receives a recording signal from an FM tuner (not shown) or other audio equipment whose signal level has been adjusted to a predetermined level in advance. The test signal generation circuit 27 is a circuit that outputs a test signal that is, for example, a 1KHz sine wave with extremely low distortion. In the normal recording mode, the input terminal 33 is connected from the recording input terminal 20 to the resistor 34. This is a mode selection switch configured to select a recording signal to be supplied through the recording level setting mode, and to select a test signal output from the test signal generation circuit 27 in the automatic recording level setting mode. The recording level adjuster 31 is a variable attenuator that attenuates the signal (recording signal or test signal) supplied from the mode selection switch 33 according to the output of a level control section 30, which will be described later.
5 is a line amplifier that amplifies the output of this recording level adjuster 31, and this line amplifier 35 is provided with a noise reduction encoder (NRE) 36. Reference numeral 37 attenuates the output of the line amplifier 35 in accordance with the sensitivity of the magnetic tape 23 (the magnetic tape being used), and consists of a variable attenuator whose attenuation amount is controlled by a sensitivity control section 38, which will be described later. There is. 39 is a recording amplifier, 40 is a recording bias oscillator, and tape sensitivity adjuster 37
After the output of is amplified by the recording amplifier 39,
The signal is superimposed on the output of the recording bias oscillator 40 and supplied to the recording head 22.

Next, 41 is the output of the playback head 24 (playback signal)
This is a playback amplifier that amplifies the
1 is provided with an equalizer circuit (EQ) 42. Further, 43 is a line amplifier that amplifies the output of the reproduction amplifier 41, and this line amplifier 43 is provided with a noise reduction decoder (NRD) 44 corresponding to the noise reduction encoder 36 described above. The output of this line amplifier 43 is supplied to the reproduction output terminal 26.

The output of the line amplifier 43 is also passed through a bandpass filter (BPF) which is installed in the MOL detection circuit 28.
45 is also supplied. This band pass filter 4
5 is a filter that passes only the 3KHz signal, which is the third harmonic component of the 1KHz test signal in this case. Further, 46 is a level detector that converts the signal level of the output of the bandpass filter 45 into a corresponding DC voltage, and 47 is a level detector that detects the level when the third harmonic distortion contained in the playback signal of the recorded test signal is 3%. A reference voltage generator 48 generates the same DC voltage as the DC voltage output by the detector 46 (that is, the DC voltage corresponding to 3% distortion), and 48 is a reference voltage generator whose output voltage of the level detector 46 is equal to the output voltage of the reference voltage generator 47. The comparator outputs a binary logic signal "1" when the signal is equal to or higher than , and otherwise outputs a "0" signal. 3 in the reproduction signal of the test signal outputted by the MOL detection circuit 28 configured as described above and the line amplifier 43 described above.
This circuit outputs a "1" signal when the harmonic distortion exceeds 3%, and a specific circuit thereof is shown in FIG. 5, for example. In this Figure 5,
The band pass filter 45 is a known band pass filter consisting of resistors 49 to 51, capacitors 52 and 53, and an operational amplifier 54.
51 and the values of capacitors 52 and 53 are set so that this bandpass filter 45 has bandpass characteristics with a center frequency of 3KHz. The level detector 46 includes resistors 55 to 57 and a diode 5.
8, 59, capacitor 60, and operational amplifier 61
This is a known rectifier circuit consisting of the following, which rectifies and outputs the output of the band pass filter 45. In the comparator 48, the output voltage of a reference voltage generator 47, which is a variable voltage source, is applied to a non-inverting input terminal, the output of the level detector 46 is supplied to an inverting input terminal, and the output terminal is connected through a resistor 62. It consists of an operational amplifier 64 connected to a positive power supply terminal 63. In this case, the output voltage of the level detector 46 is set to 3V when the third harmonic distortion of the reproduced signal of the test signal supplied to the bandpass filter 45 reaches 3%, as shown in FIG. The output voltage of the reference voltage generator 47 is also set to 3V. However, according to the MOL detection circuit 28 shown in FIG. 5, the output becomes "1" when the third harmonic distortion of the reproduction signal of the test signal becomes 3% or more.

Returning again to FIG. 4, 65 and 66 are level detectors, the level detector 65 converts the signal level of the output of the line amplifier 43 into a corresponding DC voltage, and the level detector 66 converts the signal level of the output of the line amplifier 43 into a corresponding DC voltage. It converts the signal level of the output of the amplifier 35 into a corresponding DC voltage. 67 is a comparator, and this comparator 67 detects when the output voltage of the level detector 65 is equal to or higher than the output voltage of the level detector 66, that is, the signal level of the reproduced signal becomes equal to the signal level of the recording signal. When the value is equal to or higher than that, a "1" signal is output, and in other cases, a "0" signal is output.

Next, 68 is a tape type discrimination unit that generates a code signal corresponding to the type of magnetic tape used, and includes normal tape, chrome tape, etc.
Code generator 69 corresponding to each metal tape
71, and a changeover switch 72 which is linked to a manually operated tape selection switch or a tape detection switch which automatically detects the type of tape using a sensing hole provided in the cassette half. The CPU 29 includes a sensitivity control section 38 that controls the attenuation amount of the tape sensitivity adjuster 37 based on the output of the tape type discrimination section 68 and the output of the comparator 67, and a sensitivity control section 38 that controls the attenuation amount of the tape sensitivity adjuster 37 based on the output of the tape type discrimination section 68 and the output of the MOL detection circuit 28. Recording level adjuster 3
The sensitivity control section 38 and the level control section 30 both operate according to a program stored in a memory 73 consisting of a read-only memory or a random access memory. I'm starting to do that.

Next, the operation of this embodiment having the above structure will be explained according to the flowchart shown in FIG.

First, when the magnetic tape 23 is loaded and automatic recording level setting is commanded, the mode changeover switch 33 is switched to the test signal generation circuit 27 side and an automatic recording level setting mode is started. Here, the CPU 29 reads the output of the tape type determining section 68 and determines the type of the loaded magnetic tape 23 (step S1). Next, the level control section 30 in the CPU 29 sets the attenuation amount of the recording level adjuster 31 to a value corresponding to the standard recording level corresponding to the tape type of the magnetic tape 23 (step
S2). Next, the sensitivity control section 38 in the CPU 29
Then, the attenuation amount of the tape sensitivity adjuster 37 is set to the maximum value (step S3). Once the test signal has been recorded and played back (step S4), the sensitivity control section 38 reads the output of the comparator 67 and determines whether this read value is "0" or "1" (step S4).
S5). In this case, if the read value is "0", the sensitivity control section 38 decreases the attenuation amount of the tape sensitivity adjuster 37 by one step and returns the control to step S4 (step S6), while the read value is "0". 1'', the deviation between the recording level and the reproduction level becomes zero, meaning that the recording sensitivity for the magnetic tape 23 has been corrected, and the control proceeds to step S7.

Next, after the recording sensitivity has been corrected as described above, the level adjustment section 30 sets the attenuation amount of the recording level adjuster 31 to the maximum value (step
S7). When the test signal is recorded and played back here (step S8), the MOL detection circuit 28 detects the signal level of the third harmonic included in the playback signal of the test signal, and this detection result is output from the comparator 48. (Step S9). Then, the level control section 30 reads the output of the comparator 48 and determines whether the read value is "0" or "1" (step S10). In this case, if the read value is "0", that is, if the third harmonic distortion is less than 3%, the level control unit 30 reduces the attenuation amount of the recording level adjuster 31 by one step. Increase the recording level by that amount and control step S8
(step S11); on the other hand, if the read value is "1", that is, the third harmonic distortion is 3%.
If it reaches this value, it means that the recording level adjuster 31 has been adjusted to a state where the optimum recording level corresponding to the MOL of the magnetic tape 23 can be obtained, so the attenuation amount of the recording level adjuster 31 is fixed at the same value. (Step S12). Since the setting of the optimum recording level according to the MOL of the loaded magnetic tape 23 is completed by the above operation, it is sufficient to switch the mode changeover switch 33 to the recording input terminal 20 side.

In this way, in this embodiment, the recording level can be set to the optimum recording level corresponding to the MOL of the magnetic tape 23, and the CPU 29
Since digital control is carried out using By reading out the data, it is also possible to reset the recording level extremely easily.

As explained above, the automatic recording level setting device for a tape recorder according to the present invention includes a second recording level setting circuit that automatically sets the recording level according to the level of the high frequency distortion component of the playback output signal. This makes it possible to automatically and accurately set the optimal recording level for the magnetic tape being used, thereby maximizing the dynamic range for any type of magnetic tape. It becomes possible to perform recording with extremely little distortion. Also, since the settings are automatic, anyone can easily make optimal recordings.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an example of an ALC circuit, and Figure 2 shows the operation of a conventional recording level setting device.
A diagram showing an example of the display section, FIG. 3 is a diagram showing another example of the operation and display section in a conventional recording level setting device, and FIG. 4 is an example of the present invention applied to a three-head tape recorder. FIG. 5 is a circuit diagram showing an example of a specific circuit of the MOL detection circuit in the same embodiment, FIG. 6 is a characteristic diagram showing the same circuit and its characteristics, and FIG. It is a flowchart for explaining the operation of the embodiment. 23... Magnetic tape, 27... Test signal generation circuit, 28... MOL detection circuit, 32... Recording level setting circuit.

Claims (1)

[Claims] 1. (a) A test signal generation circuit that generates a test signal to be recorded on a magnetic tape used; (b) A test signal generated by the test signal generation circuit and a recorded test signal. (c ) a bandpass filter that extracts a high frequency distortion component of the reproduced output signal; a level detector that converts the extracted high frequency distortion component into a DC voltage; a reference voltage generator that generates a predetermined reference DC voltage; Comparing means for comparing the level of the voltage and the level of the reference DC voltage and outputting a comparison result; and a recording device that amplifies or attenuates the input signal with a second signal gain and supplies the amplified or attenuated input signal to the first recording level setting circuit. A level at which the second signal gain is increased when the reference DC voltage becomes large in the comparison result between the level adjuster and the comparison means, and the second signal gain is reduced when the DC voltage becomes large. 1. An automatic recording level setting circuit for a tape recorder, comprising a second recording level setting circuit comprising a control means.