JPH0614278Y2 - Inter-track detection circuit of magnetic tape reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of an inter-track detection circuit of a magnetic tape reproducing apparatus.

First, the configuration of the inter-track detection circuit of the conventional magnetic tape reproducing apparatus
Shown in the figure. In the figure, 1 is a magnetic head, 2 is a reproduction equalizer amplifier (EQ amplifier), 3 is a level comparator, 3
-1 is a reference voltage source, 4 is a microcomputer (CP
U), 5 is a drive circuit (driver), 6 is a mechanism control device (plunger), 7 is a power amplifier (power amplifier),
Reference numeral 8 is a speaker.

The inter-track detection operation of the conventional circuit will be described with reference to FIG.

It is assumed that the reproducing signal as shown in FIG. 2 (a) is reproduced from the magnetic tape by the magnetic head 1. Fig. 2
In (a), A, A ', and A "portions indicate large signal portions, B portion indicates tape noise between songs, and C indicates small signal portions.

The reproduction signal of FIG. 2 (a) is the reproduction equalizer amplifier 2
After being amplified to a predetermined level by, the signal is input to one input terminal of the level comparator 3.

On the other hand, the other input terminal of the level comparator 3 is supplied with a fixed reference voltage for noise level determination from the reference voltage source 3-1 and the level comparator 3 outputs this reference voltage and the input signal. In comparison, when the signal level of the input signal is higher than the reference voltage, a pulse train signal as shown in FIG. 2 (c) is generated. This pulse train signal is sent to the microcomputer 4.

The microcomputer 4 monitors the generation status of the pulse train signal of FIG. 2 (c) sent from the level comparator 3,
When this pulse train signal is interrupted for a certain time (for example, 3 seconds) or more, it is determined that the portion is a music interval, and the mechanism control device 6 of the magnetic data reproducing device is sent through the drive circuit 5 to a high speed music interval detection mode. I was supposed to switch from playback mode to playback mode.

By the way, the reference voltage value of the reference voltage source 3-1 is originally
For the input signal as shown in FIG. 2 (a), the level comparator 3
Output should be set as shown in Fig. 2 (c). In order to avoid malfunction when the tape noise between songs is large, the reference voltage source 3-1 I had no choice but to reduce the sensitivity by setting it to a large value. Therefore, in the case of the conventional inter-track detection circuit, as shown in FIG. 2 (b), there is a problem that the small signal portion C in FIG. 2 (a) may be erroneously determined to be the inter-track. . Such a problem is particularly likely to occur when playing classical music having many small signal portions.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a song interval detection circuit for a magnetic tape reproducing apparatus that does not erroneously determine a small signal portion having a low recording level in a song as a song interval. And

According to the invention, the noise level of the signalless portion of the magnetic tape is detected for each attached magnetic tape, and the level of the reference voltage for detecting the track interval is changed according to the detected noise level. It is achieved by setting.

Hereinafter, the inter-track detection circuit of the present invention will be described in detail with reference to embodiments.

FIG. 3 is a block diagram showing an embodiment of the inter-track detection circuit of the present invention. In the figure, 1 is a magnetic head, 2 is a reproduction equalizer amplifier (EQ amplifier), 3 is a level comparator,
4A is a microcomputer (CPU), 5 is a drive circuit (driver), 6 is a mechanism control device (plunger),
Reference numeral 7 is a power amplifier (power amplifier), and 8 is a speaker. The same reference numerals as those in FIG. 1 indicate the same or equivalent parts.

3 is different from the conventional circuit (FIG. 1) in that the reference voltage is supplied to the level comparator 3 from the microcomputer 4A in a feedback manner.

That is, the microcomputer 4A monitors the generation state of the pulse train signal output from the level comparator 3, and when the generation of the pulse train signal is interrupted, the reference voltage value is set as a starting point from a predetermined initial value E from that time point. Gradually lower the voltage with a predetermined slope, measure the time until the falling reference voltage becomes lower than the signal level of the input signal, and measure the measured time for a predetermined fixed time (for example, 3 seconds). When it exceeds, it is determined as a music interval, and a value F = (E _n + Δ) obtained by adding a predetermined noise margin Δα to the value E _n of the reference voltage at the time when the signal level becomes smaller than the signal level of the input signal.
α) is fixedly supplied to the level comparator 3 as a reference voltage for detecting the music interval thereafter.

A control program for realizing each of the above processes and an initial value E of a reference voltage to be supplied to the level comparator 3 are stored in advance in the memory in the microcomputer 4A, and the first song after the cassette tape is loaded. The initial value E is supplied to the level comparator 3 as a reference voltage during the interval detection operation. The initial value E of the reference voltage is set to a value considerably higher than the noise level of the magnetic tape, as in the case of the conventional inter-track detection circuit described above.

Next, the inter-track detection operation of the above embodiment will be described.

Now, suppose that the position of the tape when the cassette tape is mounted on the magnetic tape reproducing apparatus is between the tracks. When the operation button of the magnetic tape reproducing device is set to the inter-track detection mode after the cassette tape is loaded, the microcomputer 4A controls the mechanism control device 6 through the drive circuit 5 to fast-forward the cassette tape. The magnetic head 1 starts the reproduction of the recording signal, and the following inter-track detection operation is performed.

First, the microcomputer 4A reads out the data of the initial value E of the built-in reference voltage,
The signal is D / D converted and supplied as an initial value E of the analog voltage to the reference voltage input terminal of the level comparator 3.

In the present case, since it is assumed that the tape position when the cassette tape is mounted is between tracks, the reproduced signal supplied from the reproduction equalizer amplifier 2 to the level comparator 3 is only the tape noise signal indicating the track. . The signal level of this tape noise signal is equal to or lower than the initial value E of the reference voltage.
Therefore, in this case, the pulse train signal is not output from the level comparator 1 even when the inter-track detection operation is started.

The microcomputer 4A monitors the generation state of the pulse train signal of the level comparator 1, and when it detects that the pulse train signal is not generated, the microcomputer 4A sets the initial value E of the reference voltage supplied to the level comparator 3 to a predetermined value. Gradually lower the slope.

As described above, when the reference voltage supplied to the level comparator 1 is gradually lowered starting from the initial value E, the reference voltage is below the tape noise level of the magnetic tape mounted at a certain time point. The voltage value is reached, at which point the level comparator 3 starts outputting the pulse train signal.

The value E _n of the reference voltage at the time the pulse train signal is generated corresponds to the tape noise level of the magnetic tape that is mounted at that time. Microcomputer 4A
Stores a value E _n of the reference voltage at this time the memory as a tape noise level of the magnetic tape that is mounted at that time. Then, a value plus the noise margin [Delta] [alpha] to a value E _n of the stored reference voltage F = (E n ₊ [Delta] [alpha]), the reference voltage for the value F detected between tracks of the magnetic tape in the subsequent Is fixedly supplied to the level comparator 3.

As a result, the reference voltage for detecting the music interval of the level comparator 3 at the time of the first music interval detection in the first music interval detection operation after mounting the cassette tape is the same as that of the conventional circuit as shown in FIG. From the initial value E of the large voltage of F to the specific reference voltage F corresponding to the tape noise level of the magnetic tape at that time.
Then, the inter-track detection operation is performed using this reference voltage F as a threshold value. Therefore, once the reference voltage F is once set, there is no possibility of erroneously detecting a portion having a low signal level in a song as a song interval as in the conventional song interval detecting circuit.

On the other hand, when the tape position when the cassette tape is loaded is the portion where the signal level is high during bending, the portion where the signal level is high is equal to or higher than the initial value E of the reference voltage.
The level comparator 3 starts outputting a pulse train signal at the same time when the inter-track detection operation is started. Therefore, the microcomputer 4A determines that the current tape position is not between the songs because the pulse train signal is output from the level comparator 3 at the same time when the song interval detecting operation starts.

Then, when the tape feed advances and the reproduction position of the tape reaches the inter-track position, the level comparator 3 displays the initial value E of the reference voltage.
Only the tape noise signal having a signal level lower than that of the above is input, and from this point, the level comparator 3 does not generate the pulse train signal. Therefore, after that, the same operation as the case where the tape position when the cassette tape is mounted is between songs is performed, and finally the level comparator 3 has F = F as a reference voltage for detecting the song interval. _{(E n} + Δ
α) is supplied.

Further, when the tape position when the cassette tape is loaded is a portion where the signal level in the song is low, the signal level may be lower than the initial value E of the reference voltage depending on the song. Therefore, in this case, the microcomputer 4A operates similarly to the case where the tape position when the cassette tape is mounted is between the tunes, and the reference voltage supplied to the level comparator 3 is set to the initial value E. The starting point is to gradually descend with a predetermined inclination.

However, since the low signal level portion is a part of the song, it does not last so long as between songs. Therefore, the interruption time of the pulse train signal from the level comparator 3 hardly lasts for a certain time or longer for the above-described inter-track detection, and before the certain time elapses, the level comparator 3 again detects the pulse train. Since the output of the signal is started, the microcomputer 4A does not judge that position to be between the songs.

Then, when the tape feed advances and the reproduction of the music portion is completed and the first inter-music portion is reached, the same operation as described above is repeated again. Pulse train signal is interrupted for a certain time or longer. Therefore, the microcomputer 4A operates in the same manner as when the tape position when the cassette tape is mounted is between tracks, and the reference voltage of the level comparator 3 is F =
It is set to _{(E n} + Δα).

As described above, no matter which tape position the track-to-track detecting operation is started, the reference voltage supplied to the level comparator 3 is the reference voltage corresponding to the tape noise level of the magnetic tape mounted at that time. F = (E _n + using the voltage E _n
Δα) is automatically set. Therefore, after that, since the inter-track detection operation of the magnetic tape is executed with this reference voltage F as a threshold value, a portion having a low signal level in the music is not erroneously detected as the inter-track.

The operation of setting the reference voltage F = (E _n + Δα) is repeated every time the mounted magnetic tape is taken out and another magnetic tape is mounted. Therefore, every time the magnetic tape is replaced, the optimum reference voltage F based on the actual tape noise level of the magnetic tape is automatically set, and the optimum reference voltage for each mounted magnetic tape is used to detect the inter-track. Can be done.

In the above embodiment, the level comparator 3 generates the pulse train signal when the input signal is larger than the reference voltage. On the contrary, when the input signal is smaller than the reference voltage, the pulse train signal is generated. Even if it is configured to generate a signal, it can be realized similarly. Also, in FIG.
An amplifier may be inserted between the reproduction equalizer amplifier 2 and the level comparator 3. A Schmitt trigger circuit can be used instead of the level comparator 3. Further, instead of the microcomputer 4A, the setting operation of the reference voltage F of the level comparator 3 described above may be performed by a logic circuit having a hardware configuration.

As described above, according to the present invention, the noise level of the signalless portion of the magnetic tape is detected for each magnetic tape, and the reference voltage level for detecting the inter-track distance is detected according to the detected noise level. Since it is variably set for each magnetic tape, it is possible to set an accurate reference voltage according to the noise level of the unrecorded part of the magnetic tape to be mounted, like the conventional inter-track detection circuit. It is possible to prevent the low signal level portion in a song from being erroneously detected as a song interval.

[Brief description of drawings]

FIG. 1 is a block diagram of a conventional inter-track detection circuit, FIG. 2 is a waveform diagram for explaining the operation of the conventional inter-track detection circuit, and FIG. 3 is a block diagram showing an embodiment of the present invention. The figure is a waveform diagram for explaining the operation of the embodiment. 1 ... Playback head, 2 ... Playback equalizer amplifier, 3 ...
… Level comparator, 4A… Microcomputer, 5…
... Drive circuit, 6 ... Mechanism control device.

Claims (1)

[Scope of utility model registration request] 1. A signal input terminal for inputting a reproduction signal from a magnetic head in a music interval detecting circuit of a magnetic tape reproducing device for detecting a signal level of a recording signal recorded on a magnetic tape to detect a music interval. And a reference voltage input terminal to which a reference voltage for level comparison is input, level comparison means for comparing and detecting the signal level of the input signal and the reference voltage, and an initial value of the reference voltage to the level comparison means. As an initial voltage supply means for supplying a voltage of a value larger than the noise level of the magnetic tape, and an output generation state of the level comparison means is monitored, and the starting point is the time when the input signal becomes smaller than the initial value of the reference voltage. As the reference voltage lowering means for gradually lowering the initial value of the reference voltage with a predetermined slope, the reference voltage lowered by the reference voltage lowering means is lower than the input signal. A time measuring means for measuring the time until it becomes small, a music interval judging means for judging that there is a music interval only when the measured time exceeds a predetermined fixed time, and a music interval determining means for measuring the music interval. After that, a voltage obtained by adding a predetermined anti-noise margin to the value of the reference voltage when it becomes smaller than the input signal is used as the reference for detecting the inter-track distance of the magnetic tape mounted at that time. And a reference voltage setting means for fixedly supplying the level comparing means as a voltage.