JPH0329165A - Recording mode discriminating device - Google Patents

Abstract

PURPOSE:To accurately discriminate a recording mode even when the amplitude of a reproduced FM signal is dropped by discriminating the recording mode based upon a signal proportional to the instantaneous frequency of the reproduced FM signal obtained by demodulating the reproduced FM signal. CONSTITUTION:An FM signal recorded with either one of two recording modes having different FM carrier frequency levels is reproduced from a magnetic tape and inputted to an input terminal 1 as a reproduced FM signal. The FM demodulating circuit 10 executes FM modulation, and outputs the signal proportional to the instantaneous frequency of the reproduced FM signal. Thereby, the DC level of an output signal from an FM demodulating circuit 10 is proportional to the carrier frequency of the reproduced FM signal. The FM- demodulated signal is inputted to a recording mode discriminating device 15 by DC connection so that its DC component is also transmitted and the DC component is extracted, so that the signal corresponding to the FM carrier frequency can be extracted and the recording mode can be discriminated. Thus, the recording mode can be accurately discriminated in accordance with the carrier frequency of the reproduced FM signal without depending upon the amplitude of the reproduced FM signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a device for determining the recording mode during playback in a VTR having recording modes based on two different FMIri transmission frequencies.

In a conventional home VTR, a luminance signal is FM modulated and recorded on a magnetic tape. Incidentally, in recent years, in order to perform high-quality recording with higher resolution, a recording method (for example, the SVHS method) has been developed in which the carrier wave frequency during FM modulation of the luminance signal is higher than that of the conventional method. V like this
In TR, in order to make it possible to reproduce recorded signals using conventional recording systems with low FM carrier frequencies (e.g. VHS system), it is necessary to determine which of two recording modes was used to record. It becomes necessary.

A conventional recording mode discrimination device will be described below.

In the following description, of the two recording modes with different FM@transmission frequencies, the recording mode with the higher FMllil transmission frequency will be referred to as A mode, and the lower recording mode will be referred to as B mode.

FIG. 3 is a composition diagram showing a conventional recording mode discriminating device. Signals recorded in either A mode or B mode are reproduced from the magnetic tape and input to input terminal 1. This signal is input to the bandpass filter 2. Here, the bandpass filter 2 is a B-mode FMII
This is a characteristic that allows a band near the I transmission frequency to pass. Therefore, if the reproduced signal is one recorded by the B mote, the output of the bandpass filter 2 will be a sine wave with a relatively large amplitude. On the other hand, the reproduced signal is A
mode, the output of the bandpass filter 2 will be a signal of small amplitude. This signal is rectified in a rectifier circuit 3, and then a peak value of the amplitude is detected in a peak hold circuit 4. The detected peak value has noise components removed by a low-pass filter 5, and is input to a comparison circuit 6. Comparison circuit 6
Now, the amplitude will be compared with the reference value signal 8. The reference value signal 8 is the output amplitude of the low-pass filter 5 in the case of A mode and the B
It is preset to the intermediate value of the output amplitude for the mode. Therefore, when the output amplitude of the low-pass filter 5 is smaller than the reference signal 8, it is determined to be the A mode, and when it is larger, it is determined to be the B mode, and a discrimination signal is outputted from the discrimination signal output terminal 7.

Such a conventional recording mode discriminating device is shown in, for example, Japanese Patent Laid-Open Publication No. 62-293896.

Problems to be Solved by the Invention However, in the conventional device described above, the determination result depends on the amplitude of the reproduced FM signal. Therefore, if the amplitude of the reproduced FM signal decreases significantly during special playback such as search or still, or if the amplitude of the reproduced FM signal decreases due to changes in the magnetic tape or magnetic head over time,
There was a problem with incorrect judgments being made.

In order to solve the above-mentioned problems, the present invention provides a recording method that accurately determines the recording mode even when the amplitude of the reproduced FM signal decreases due to special reproduction or changes over time, without depending on the amplitude of the reproduced FM signal. The present invention aims to provide a mode discrimination device.

Means for Solving the Problems In order to achieve the above object, the recording mode discriminating device of the present invention includes a smoothing means for smoothing a demodulated reproduced FM signal, and an output signal value of the smoothing means and a predetermined reference value. and a comparison means for comparison, and outputs a discrimination signal according to the comparison result by the comparison means.

Operation The present invention uses the above-described structure to determine the recording mode based on a signal proportional to the frequency of the reproduced FM signal, which is obtained by demodulating the reproduced FM signal. For this reason,
The recording mode can be accurately determined according to the carrier frequency of the reproduced FM signal without depending on the amplitude of the reproduced FM signal.

Embodiment Hereinafter, in the description of the embodiment of the present invention, as in the case of the conventional example, of the two recording modes with different FM carrier frequencies, the recording mode with the higher FMvi transmission frequency is mode A, and the recording mode with the lower FMvi transmission frequency is the mode A. Let's call it B mode.

A first embodiment of the recording mode discrimination device of the present invention will be described below. FIG. 1 shows the configuration of a first embodiment of the recording mode discriminating device of the present invention and an FM demodulation circuit located in the preceding stage thereof. In FIG. 1, input/output terminals having the same functions as those of the conventional example shown in FIG. 3 are given the same numbers. In FIG. 1, an FM signal recorded in either A mode or B mode is reproduced from a magnetic tape and input as a reproduced FM signal to a human input terminal l. The FMl [modulation circuit IO performs FM demodulation and outputs a signal proportional to the instantaneous frequency of the reproduced FM signal. Therefore, the DC level of the output signal of the FM demodulation circuit IO is proportional to the carrier frequency of the reproduced FM signal. The FM demodulated signal is input to the recording mode discrimination device 15 through DC coupling so that the DC component is also transmitted.

Note that this FMlgiJ circuit 10 does not need to be newly provided for the recording mode discrimination device 15. That is, F.M.
The VTR is provided in advance to demodulate the modulated luminance signal, and the output of the FM demodulation circuit 10 is guided from the demodulation output terminal 13 to the luminance signal reproduction processing circuit of the VTR.

Now, the configuration and operation of the recording mode discriminating device 15 will be explained. The output signal of the FM demodulation circuit IO is smoothed in a low-pass filter 11 to remove the luminance signal component, and a DC precept is output. As described above, this DC component is proportional to the carrier wave frequency. Therefore,
A unique DC value is obtained for each of A mode and B mode having different carrier frequencies. Low pass filter 11
The output of is input to the comparison circuit l2. Here, the reference value signal 14 is predetermined near the middle between the DC value corresponding to the A mode and the DC value corresponding to the B mode. Therefore, by comparing the output value of the low-pass filter 11 and the reference value signal 14 in the comparator circuit 12, it is possible to determine which recording mode is in use. The determination result is output from the determination signal output terminal 7.

As described above, in this embodiment, the FMIII transmission frequency is determined by extracting the DC component based on the signal proportional to the instantaneous frequency of the reproduced FM signal obtained by demodulating the reproduced FM signal. The recording mode is determined by extracting the signal corresponding to the . Therefore, even if the amplitude of the reproduced FM signal decreases due to special reproduction or changes over time, the recording mode can be accurately determined.

Next, a second embodiment of the present invention will be described.

FIG. 2 shows the configuration of a second embodiment of the recording mode discriminating device of the present invention, and the FMl adjustment circuit located in the preceding stage thereof. In Fig. 2, the same numbers are given to broncs having the same functions as those of the first embodiment shown in Fig. 1. Regarding the recording mode discriminating device 25 shown in FIG. 2, only the parts that are different from the embodiment shown in FIG. 1 will be explained. In the recording mode discriminating device 15 according to the first embodiment shown in FIG. need to be characterized. Therefore, the circuit scale may become large. Therefore, in the recording mode discrimination device 25 according to the second embodiment shown in FIG. 2, the binary signal discriminated by the comparison circuit 12 is further input to the low-pass filter 16. In the low-pass filter 16, the signal from which long-term dropouts and effects of low-frequency noise have been removed is set to a value that is near the middle of the two values of the binary signal that is the output of the comparator circuit 12. reference value signal 18
It is also input to the comparator circuit l7. The comparison circuit 17 compares the output value of the low-pass filter 16 with the reference value signal 18, and outputs the comparison result from the discrimination signal output terminal 7 as a discrimination output.

With the above configuration, the low-pass filter l1 does not need to have narrow band characteristics, and the recording mode can be determined with a small circuit scale without being affected by dropouts or low-frequency noise. .

Further, since the output of the comparison circuit 12 is a binary signal, the low-pass filter 16 and the comparison circuit 17 can be easily realized with a simple digital circuit.

Note that the comparison circuits 12 and 17 in the first and second embodiments described above may have hysteresis characteristics in order to prevent the chattering phenomenon.

Effects of the Invention As described above, according to the present invention, the recording mode is determined based on a signal proportional to the instantaneous frequency of the reproduced FM signal, which is obtained by demodulating the reproduced FM signal. Therefore, even if the amplitude of the reproduced FM signal decreases due to special reproduction or changes over time, the recording mode can be accurately determined. Furthermore, by providing two comparison circuits as in the second embodiment, the circuit scale is small and the recording mode can be determined without being affected by dropouts or the like.

[Brief explanation of drawings]

Fig. 1 is a structural diagram showing a first embodiment of an FM demodulation circuit and a recording mode discrimination device of the present invention, and Fig. 2 shows a second embodiment of an FM demodulation circuit and a recording mode discrimination device of the present invention. Fig. 3 is a structural diagram showing a conventional recording mode discriminating device. 10...FM demodulation circuit, 11. 16...
...Low pass filter, 12. 17... Comparison circuit. Figure 1 LΣI! O Kayage-do PII Ushio J Tadashi I

Claims (2)

[Claims] (1) smoothing means for smoothing the demodulated reproduced FM signal;
A recording mode discriminating device comprising a comparing means for comparing an output signal value of the smoothing means and a predetermined reference value, and outputting a discriminating signal according to a comparison result by the comparing means. (2) a first smoothing means for smoothing the demodulated reproduced FM signal; a first comparison means for comparing the output signal value of the first smoothing means with a first reference value; a second smoothing means for smoothing the comparison result by the comparing means; and a second comparing means for comparing the output signal value of the second smoothing means and a second reference value, the second comparing means A recording mode discrimination device that outputs a discrimination signal according to the comparison result.