JPS6044737B2 - How to play - Google Patents

Description

[Detailed Description of the Invention] A VTR (video tape recorder) not only plays back at the normal tape speed at which it is recorded (hereinafter referred to as normal playback), but also plays the tape at high speeds such as when fast forwarding or rewinding. There are cases where regeneration (hereinafter referred to as high-speed regeneration) is performed while the vehicle is running.

By the way, in the case of this high-speed reproduction, the frequency of the reproduced high-frequency signal is significantly shifted from that during normal reproduction.

However, since the reproduction equalizer has characteristics for the reproduced signal during normal reproduction, if you try to demodulate the reproduced signal as it is during high-speed reproduction, the reproduced image has the disadvantage that the image quality will deteriorate considerably. The present invention aims to provide a regeneration method that can effectively eliminate this drawback.

An example of the reproduction method according to the present invention will be described below.
Let's explain the case of R. FIG. 1 shows an example of a reproduction system using the method of the present invention, where 1 is a switch for switching between normal reproduction and high-speed reproduction.

During normal playback, the switch 1 is connected to the contact N, and the rotating magnetic head 2 produces a playback output with a frequency spectrum as shown in FIG. The signal is supplied to a reproduction equalizer circuit 4 through a switch 1, the output of the reproduction equalizer circuit 4 is supplied to a demodulation circuit 5, where it is demodulated, and the demodulated output is supplied to a gain control amplifier 6.

A voltage corresponding to the tape speed is supplied from a terminal 7 to the gain control amplifier 6, and the gain is controlled thereby.
The purpose of this gain control circuit is to correct level changes in the reproduced video signal depending on the speed during high-speed reproduction, as will be described later. And this gain control amplifier 6
An output terminal 8 is led out, and a reproduced video signal is taken out to this terminal 8.

Next, during high-speed reproduction, for example, when reproduction is performed in a fast-forward state at a tape speed m or more times that of normal reproduction, switch 1 is connected to contact F.

At this time, as shown in FIG. 2B, the head 2 obtains a reproduced output Sx whose center frequency is at a frequency fx that is significantly lower than 10 MH2, and this is supplied to the frequency converter 9. On the other hand, this frequency converter 9 is supplied with an oscillation signal Sv of frequency fv from a variable frequency oscillator 10, and from this, a signal Sx from an amplifier 3 and a signal Sv from an oscillator 1 are supplied.
Signals having the sum and difference frequencies with the oscillation signal Sv from 0 are obtained.

In this case, the variable frequency oscillator 10 has a free-running center frequency, for example, an oscillator whose oscillation frequency is controlled by a voltage corresponding to the tape speed from the terminal 7. When the center frequency of the retrieved reproduction output becomes Fx=10M11z+Δf, the oscillation frequency Fv of the oscillator 10 is controlled to become Fv=40MHZ+Δf.

Therefore, the signal with the frequency difference between the signal Sx and the signal Sv is:
Fv-Fx=30M, and the signal S has a constant center frequency even if the tape speed changes.

(See Figure 2C). Then, a signal SD having a frequency that is the difference between these two signals is extracted from the bandpass filter 11, and this signal SD is supplied to the frequency converter 12. On the other hand, this frequency converter 12 is supplied with a constant frequency FO=Shunda signal Sc from a crystal oscillator 13, and a signal SO (second (see Figure D), a signal is obtained by taking the sum, and the signal SO is taken out through a bandpass filter 14 having a pass characteristic as shown in Figure 2E.

This signal SO has a center frequency of FO-(Fv-Fx)=
10M1I2', amplifier 3 during normal playback
The output signal is similar to that of .

And this signal S. is supplied to the reproduction equalizer circuit 4 through the contact F of the switch 1, and demodulated by the demodulator 5. In this case, since there is no deviation change in the frequency modulated wave before demodulation, the level of the video signal, which is the demodulated output, changes depending on the change in tape speed. There will be a difference in the
Therefore, in the present invention, the demodulated output is supplied to the gain control amplifier 6, and the gain control amplifier 6 is controlled by a voltage that changes in response to changes in tape speed, so that the demodulated video signal taken out from the terminal 8 is , -j is kept at a constant level regardless of changes in tape speed. In this way, even in the case of high-speed reproduction, it is possible to obtain a reproduction signal that always provides a good reproduction image.

By the way, in the example of Fig. 1, frequency conversion is performed twice to obtain a signal with the same frequency as during normal reproduction, but as shown in Fig. 3A, the variable frequency of the example of Fig. 1 is Set the free-running center frequency Fv of the oscillator 10 to twice the reproduction center frequency during normal reproduction, or 20M in the case of the example in Fig. 1.
Hz, the frequency converter 9 can obtain a signal with a center frequency of 10 MHz as shown in FIG. The question may arise as to whether this is the case.

However, this causes the following inconvenience. That is, in the case of this one-time conversion, in order to obtain the case where the center frequency is JlO ox, the output of the frequency converter 9 is passed through a bandpass filter having a pass characteristic as shown in FIG. 3C. However, as is clear from the figure, this bandpass filter not only provides a signal converted to the center frequency 1/Z as shown in figure D, but also the output of amplifier 3 shown in figure A. This is undesirable since there is a risk that the signal may be taken out as is.

In addition, as shown by O and × in Figure 3, the signal obtained as a difference in one frequency conversion has frequencies higher and lower than the center frequency of the original signal. Since the relationship is reversed, it is not possible to perform good demodulation using the same reproduction equalizer circuit and demodulator as in normal reproduction.

However, if we adopt the playback method shown in Figure 4,
Frequency conversion only needs to be done once.

That is, in this example, the output signal of the amplifier 3 is supplied to the contact N of the switch 1 through the equalizer circuit 15 for normal reproduction and the demodulation circuit 16 for normal reproduction.

The output signal of the amplifier 3 is also supplied to the frequency converter 9, where it is multiplied by the signal from the variable frequency oscillator 10 as in the example of FIG. SD is obtained. In this example, this signal SO passes through the equalizer circuit 17 for high-speed reproduction and the demodulation circuit 18 for high-speed reproduction to the switch 1.
is supplied to contact F. The signal obtained by this switch 1 is then supplied to a gain control amplifier 6. In this way, each equalizer circuit 15 and 17, each demodulation circuit 1
6 and 18 can each have desired characteristics, so that good reproduction and demodulation can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a reproduction system for explaining an example of the method of this invention, FIGS. 2 and 3 are frequency characteristic diagrams for explaining the same, and FIG. 4 is another example of the method of this invention. 1 is a diagram showing an example of a reproduction system for explaining. 1 is a switch, 2 is a rotating magnetic head, 4 is a reproduction equalizer circuit, 5 is a demodulation circuit, 6 is a gain control amplifier, 7 is a voltage converter according to the tape speed, and 9 and 12 are frequency converters, 10 is a variable The frequency oscillators 11 and 14 are bandpass filters.

Claims (1)

[Claims] 1 When reproducing by running a recording medium at a faster transport speed than during recording, the reproduced signal is mixed with a frequency signal that changes according to the speed of the recording medium, and the mixed output is passed through a filter to extract a signal in a specific band. , a reproducing method in which the output signal of this filter is demodulated, and the gain of the demodulated signal is controlled according to the transport speed of the recording medium.